libs/core/runtime/jsruntime.rs - main - githubmirror/deno

libs/core/runtime/jsruntime.rs
3 702 строки130 KB
Bartek Iwańczuk
perf(core): run the common-path tick drain in Rust (#36157)
27 июл 2026, 15:59
27 июл 2026, 15:590c965f5
// Copyright 2018-2026 the Deno authors. MIT license.

use std::any::Any;
use std::cell::Cell;
use std::cell::RefCell;
use std::collections::HashMap;
use std::collections::VecDeque;
use std::ffi::c_void;
use std::future::Future;
use std::future::poll_fn;
use std::mem::ManuallyDrop;
use std::ops::Deref;
use std::ops::DerefMut;
use std::pin::Pin;
use std::rc::Rc;
use std::sync::Arc;
use std::sync::Mutex;
use std::sync::OnceLock;
use std::task::Context;
use std::task::Poll;
use std::task::Waker;
use std::time::Instant;

use deno_error::JsErrorBox;
use futures::FutureExt;
use futures::StreamExt;
use futures::task::AtomicWaker;
use smallvec::SmallVec;

fn startup_phases_enabled() -> bool {
  static ENABLED: OnceLock<bool> = OnceLock::new();
  *ENABLED.get_or_init(|| {
    // Diagnostic env var — only consulted once per process. Bypassing
    // `sys_traits` here is intentional: the snapshot/runtime layers don't
    // thread an `EnvProvider` through this code path, and this opt-in
    // tracing is only useful when running an actual `deno` binary anyway.
    #[allow(
      clippy::disallowed_methods,
      reason = "diagnostic env var; not part of the sys_traits surface"
    )]
    let v = std::env::var_os("DENO_STARTUP_PHASES");
    v.is_some_and(|v| !v.is_empty() && v != "0")
  })
}

#[inline]
fn startup_phase_begin() -> Option<Instant> {
  if startup_phases_enabled() {
    Some(Instant::now())
  } else {
    None
  }
}

#[inline]
fn startup_phase_end(t: Option<Instant>, label: &str) {
  if let Some(start) = t {
    let elapsed = start.elapsed();
    #[allow(clippy::print_stderr, reason = "diagnostic")]
    {
      eprintln!("[startup] {label:>32}  {elapsed:?}");
    }
  }
}

use super::SnapshotStoreDataStore;
use super::SnapshottedData;
use super::bindings;
use super::bindings::create_exports_for_ops_virtual_module;
use super::bindings::watch_promise;
use super::exception_state::ExceptionState;
use super::jsrealm::JsRealmInner;
use super::op_driver::OpDriver;
use super::setup;
use super::snapshot;
use super::stats::RuntimeActivityStatsFactory;
use super::v8_static_strings::*;
use crate::Extension;
use crate::ExtensionArguments;
use crate::ExtensionFileSource;
use crate::ExtensionFileSourceCode;
use crate::FastStaticString;
use crate::FastString;
use crate::ModuleCodeString;
use crate::NoopModuleLoader;
use crate::OpMetadata;
use crate::OpMetricsEvent;
use crate::OpStackTraceCallback;
use crate::OpState;
use crate::ascii_str;
use crate::ascii_str_include;
use crate::cppgc::FunctionTemplateData;
use crate::error::CoreError;
use crate::error::CoreErrorKind;
use crate::error::CoreModuleExecuteError;
use crate::error::CoreModuleParseError;
use crate::error::ExtensionLazyInitCountMismatchError;
use crate::error::ExtensionLazyInitOrderMismatchError;
use crate::error::JsError;
use crate::error::exception_to_err_result;
use crate::extension_set;
use crate::extension_set::LoadedSources;
use crate::extensions::GlobalObjectMiddlewareFn;
use crate::extensions::GlobalTemplateMiddlewareFn;
use crate::inspector::JsRuntimeInspector;
use crate::module_specifier::ModuleSpecifier;
use crate::modules::CustomModuleEvaluationCb;
use crate::modules::EvalContextCodeCacheReadyCb;
use crate::modules::EvalContextGetCodeCacheCb;
use crate::modules::ExtCodeCache;
use crate::modules::ExtModuleLoader;
use crate::modules::IntoModuleCodeString;
use crate::modules::IntoModuleName;
use crate::modules::ModuleId;
use crate::modules::ModuleLoader;
use crate::modules::ModuleMap;
use crate::modules::ModuleName;
use crate::modules::RequestedModuleType;
use crate::modules::SideModuleKind;
use crate::modules::ValidateImportAttributesCb;
use crate::modules::recursive_load::RecursiveModuleLoad;
use crate::modules::script_origin;
use crate::ops_metrics::OpMetricsFactoryFn;
use crate::ops_metrics::dispatch_metrics_async;
use crate::runtime::ContextState;
use crate::runtime::JsRealm;
use crate::runtime::OpDriverImpl;
use crate::runtime::jsrealm;
use crate::runtime::jsrealm::IMM_IDX_COUNT;
use crate::runtime::jsrealm::IMM_IDX_HAS_OUTSTANDING;
use crate::runtime::jsrealm::IMM_IDX_REF_COUNT;
use crate::source_map::SourceMapData;
use crate::source_map::SourceMapper;
use crate::stats::RuntimeActivityType;
use crate::uv_compat;

pub type WaitForInspectorDisconnectCallback = Box<dyn Fn()>;

/// A per-isolate hook invoked when V8's host-initialize-import-meta callback
/// fires for a module that is not registered in deno_core's module map (e.g.
/// a `node:vm` `SourceTextModule`). The embedder is expected to populate the
/// `meta` object as needed and return; the hook is not allowed to throw.
///
/// Each argument carries its own lifetime parameter (rather than being tied
/// to the scope's `'s`) so the unbound `Local`s V8 passes into the
/// extern "C" callback can be forwarded without re-creating handles.
pub type ExternalModuleImportMetaCb = for<'s, 'i, 'm, 'o> fn(
  scope: &mut v8::PinScope<'s, 'i>,
  module: v8::Local<'m, v8::Module>,
  meta: v8::Local<'o, v8::Object>,
);

const STATE_DATA_OFFSET: u32 = 0;

pub type ExtensionTranspiler =
  dyn Fn(
    ModuleName,
    ModuleCodeString,
  ) -> Result<(ModuleCodeString, Option<SourceMapData>), JsErrorBox>;

/// Objects that need to live as long as the isolate
#[derive(Default)]
pub(crate) struct IsolateAllocations {
  pub(crate) externalized_sources: Box<[v8::OneByteConst]>,
  pub(crate) original_sources: Box<[FastString]>,
  /// Specifiers of the externalized `lazy_loaded_*` sources, parallel to the
  /// trailing entries of `original_sources` (only populated when building a
  /// snapshot). Used at serialize time to drop the bytes of *non-consumed*
  /// lazy sources from the snapshot sidecar — their external-reference slots
  /// must stay (for index alignment) but nothing references them, so storing
  /// empty bytes avoids duplicating residual sources (which the binary already
  /// ships via the residual table).
  pub(crate) lazy_source_specifiers: Box<[ModuleName]>,
  pub(crate) near_heap_limit_callback_data:
    Option<(Box<RefCell<dyn Any>>, v8::NearHeapLimitCallback)>,
}

/// ManuallyDrop<Rc<...>> is clone, but it returns a ManuallyDrop<Rc<...>> which is a massive
/// memory-leak footgun.
pub(crate) struct ManuallyDropRc<T>(ManuallyDrop<Rc<T>>);

impl<T> ManuallyDropRc<T> {
  #[allow(unused, reason = "used in other configurations")]
  pub fn clone(&self) -> Rc<T> {
    self.0.deref().clone()
  }
}

impl<T> Deref for ManuallyDropRc<T> {
  type Target = Rc<T>;
  fn deref(&self) -> &Self::Target {
    self.0.deref()
  }
}

impl<T> DerefMut for ManuallyDropRc<T> {
  fn deref_mut(&mut self) -> &mut Self::Target {
    self.0.deref_mut()
  }
}

/// This struct contains the [`JsRuntimeState`] and [`v8::OwnedIsolate`] that are required
/// to do an orderly shutdown of V8. We keep these in a separate struct to allow us to control
/// the destruction more closely, as snapshots require the isolate to be destroyed by the
/// snapshot process, not the destructor.
///
/// The way rusty_v8 works w/snapshots is that the [`v8::OwnedIsolate`] gets consumed by a
/// [`v8::snapshot::SnapshotCreator`] that is stored in its annex. It's a bit awkward, because this
/// means we cannot let it drop (because we don't have it after a snapshot). On top of that, we have
/// to consume it in the snapshot creator because otherwise it panics.
///
/// This inner struct allows us to let the outer JsRuntime drop normally without a Drop impl, while we
/// control dropping more closely here using ManuallyDrop.
pub(crate) struct InnerIsolateState {
  will_snapshot: bool,
  extensions: Vec<&'static str>,
  op_count: usize,
  source_count: usize,
  addl_refs_count: usize,
  main_realm: ManuallyDrop<JsRealm>,
  pub(crate) state: ManuallyDropRc<JsRuntimeState>,
  v8_isolate: ManuallyDrop<v8::OwnedIsolate>,
}

impl InnerIsolateState {
  /// Clean out the opstate and take the inspector to prevent the inspector from getting destroyed
  /// after we've torn down the contexts. If the inspector is not correctly torn down, random crashes
  /// happen in tests (and possibly for users using the inspector).
  pub fn prepare_for_cleanup(&mut self) {
    // Explicitly shut down the op driver here, just in case there are other references to it
    // that prevent it from dropping after we invalidate the state.
    self.main_realm.0.context_state.pending_ops.shutdown();
    let inspector = self.state.inspector.take();
    self.state.op_state.borrow_mut().clear();
    if let Some(inspector) = inspector {
      assert_eq!(
        Rc::strong_count(&inspector),
        1,
        "The inspector must be dropped before the runtime"
      );
    }
  }

  pub fn cleanup(&mut self) {
    // Shut down the op driver and take the inspector before realm destroy.
    self.main_realm.0.context_state.pending_ops.shutdown();
    let inspector = self.state.inspector.take();

    // Unregister isolate waker before dropping the isolate
    let isolate_ptr = unsafe { self.v8_isolate.as_raw_isolate_ptr() };
    setup::unregister_isolate(setup::isolate_ptr_to_key(isolate_ptr));

    let state_ptr = self.v8_isolate.get_data(STATE_DATA_OFFSET);
    // SAFETY: We are sure that it's a valid pointer for whole lifetime of
    // the runtime.
    _ = unsafe { Rc::from_raw(state_ptr as *const JsRuntimeState) };

    // Destroy the realm while the uv_loop (stored in op_state's
    // gotham_state) is still alive. destroy() reads uv_loop_ptr to
    // release the Global<Context> stored in loop.data. If we clear
    // op_state first, the Box<UvLoop> is freed and destroy() would
    // dereference a dangling pointer (use-after-free).
    unsafe {
      ManuallyDrop::take(&mut self.main_realm).0.destroy();
    }

    // Now safe to clear op_state (drops Box<UvLoop> etc.) since
    // destroy() has already released the Global from loop.data.
    self.state.op_state.borrow_mut().clear();
    if let Some(inspector) = inspector {
      assert_eq!(
        Rc::strong_count(&inspector),
        1,
        "The inspector must be dropped before the runtime"
      );
    }

    debug_assert_eq!(Rc::strong_count(&self.state), 1);
  }

  pub fn prepare_for_snapshot(mut self) -> v8::OwnedIsolate {
    self.cleanup();

    // SAFETY: We're copying out of self and then immediately forgetting self
    unsafe {
      ManuallyDrop::drop(&mut self.state.0);

      let isolate = ManuallyDrop::take(&mut self.v8_isolate);

      std::mem::forget(self);

      isolate
    }
  }
}

impl Drop for InnerIsolateState {
  fn drop(&mut self) {
    self.cleanup();
    // SAFETY: We gotta drop these
    unsafe {
      ManuallyDrop::drop(&mut self.state.0);

      if self.will_snapshot {
        // Create the snapshot and just drop it.
        #[allow(
          clippy::print_stderr,
          reason = "intentional warning about leaked isolate"
        )]
        {
          eprintln!("WARNING: v8::OwnedIsolate for snapshot was leaked");
        }
      } else {
        ManuallyDrop::drop(&mut self.v8_isolate);
      }
    }
  }
}

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub(crate) enum InitMode {
  /// We have no snapshot -- this is a pristine context.
  New,
  /// We are using a snapshot, thus certain initialization steps are skipped.
  FromSnapshot {
    // Can we skip the work of op registration?
    skip_op_registration: bool,
  },
}

impl InitMode {
  fn from_options(options: &RuntimeOptions) -> Self {
    match options.startup_snapshot {
      None => Self::New,
      Some(_) => Self::FromSnapshot {
        skip_op_registration: options.skip_op_registration,
      },
    }
  }

  #[inline]
  pub fn needs_ops_bindings(&self) -> bool {
    !matches!(
      self,
      InitMode::FromSnapshot {
        skip_op_registration: true
      }
    )
  }
}

#[derive(Default)]
struct PromiseFuture {
  resolved: Cell<Option<Result<v8::Global<v8::Value>, Box<JsError>>>>,
  waker: Cell<Option<Waker>>,
}

#[derive(Clone, Default)]
struct RcPromiseFuture(Rc<PromiseFuture>);

impl RcPromiseFuture {
  pub fn new(res: Result<v8::Global<v8::Value>, Box<JsError>>) -> Self {
    Self(Rc::new(PromiseFuture {
      resolved: Some(res).into(),
      ..Default::default()
    }))
  }
}

impl Future for RcPromiseFuture {
  type Output = Result<v8::Global<v8::Value>, Box<JsError>>;

  fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
    let this = self.get_mut();
    match this.0.resolved.take() {
      Some(resolved) => Poll::Ready(resolved),
      _ => {
        this.0.waker.set(Some(cx.waker().clone()));
        Poll::Pending
      }
    }
  }
}

static VIRTUAL_OPS_MODULE_NAME: FastStaticString = ascii_str!("ext:core/ops");

pub(crate) struct InternalSourceFile {
  pub specifier: FastStaticString,
  pub source: FastStaticString,
}

macro_rules! internal_source_file {
  ($str_:literal) => {{
    InternalSourceFile {
      specifier: ascii_str!(concat!("ext:core/", $str_)),
      source: ascii_str_include!(concat!("../", $str_)),
    }
  }};
}

/// These files are executed just after a new context is created. They provided
/// the necessary infrastructure to bind ops.
pub(crate) static CONTEXT_SETUP_SOURCES: [InternalSourceFile; 2] = [
  internal_source_file!("00_primordials.js"),
  internal_source_file!("00_infra.js"),
];

/// These files are executed when we start setting up extensions. They rely
/// on ops being already fully set up.
pub(crate) static BUILTIN_SOURCES: [InternalSourceFile; 2] = [
  internal_source_file!("02_timers.js"),
  internal_source_file!("01_core.js"),
];

/// Executed after `BUILTIN_SOURCES` are executed. Provides a thin ES module
/// that exports `core`, `internals` and `primordials` objects.
pub(crate) static BUILTIN_ES_MODULES: [ExtensionFileSource; 1] =
  [ExtensionFileSource::new(
    "ext:core/mod.js",
    ascii_str_include!("../mod.js"),
  )];

/// We have `ext:core/ops` and `ext:core/mod.js` that are always provided.
#[cfg(test)]
pub(crate) const NO_OF_BUILTIN_MODULES: usize = 2;

/// A single execution context of JavaScript. Corresponds roughly to the "Web
/// Worker" concept in the DOM.
///
/// The JsRuntime future completes when there is an error or when all
/// pending ops have completed.
///
/// Use [`JsRuntimeForSnapshot`] to be able to create a snapshot.
///
/// Note: since V8 11.6, all runtimes must have a common parent thread that
/// initalized the V8 platform. This can be done by calling
/// [`JsRuntime::init_platform`] explicitly, or it will be done automatically on
/// the calling thread when the first runtime is created.
pub struct JsRuntime {
  pub(crate) inner: InnerIsolateState,
  pub(crate) allocations: IsolateAllocations,
  // Contains paths of source files that were executed in
  // [`JsRuntime::init_extension_js`]. This field is populated only if a
  // snapshot is being created.
  files_loaded_from_fs_during_snapshot: Vec<&'static str>,
  // Marks if this is considered the top-level runtime. Used only by inspector.
  is_main_runtime: bool,
}

/// The runtime type used for snapshot creation.
pub struct JsRuntimeForSnapshot(JsRuntime);

impl Deref for JsRuntimeForSnapshot {
  type Target = JsRuntime;

  fn deref(&self) -> &Self::Target {
    &self.0
  }
}

impl DerefMut for JsRuntimeForSnapshot {
  fn deref_mut(&mut self) -> &mut Self::Target {
    &mut self.0
  }
}

pub struct CrossIsolateStore<T>(Arc<Mutex<CrossIsolateStoreInner<T>>>);

struct CrossIsolateStoreInner<T> {
  map: HashMap<u32, T>,
  last_id: u32,
}

impl<T> CrossIsolateStore<T> {
  pub(crate) fn insert(&self, value: T) -> u32 {
    let mut store = self.0.lock().unwrap();
    let last_id = store.last_id;
    store.map.insert(last_id, value);
    store.last_id += 1;
    last_id
  }

  pub(crate) fn take(&self, id: u32) -> Option<T> {
    let mut store = self.0.lock().unwrap();
    store.map.remove(&id)
  }
}

impl<T> Default for CrossIsolateStore<T> {
  fn default() -> Self {
    CrossIsolateStore(Arc::new(Mutex::new(CrossIsolateStoreInner {
      map: Default::default(),
      last_id: 0,
    })))
  }
}

impl<T> Clone for CrossIsolateStore<T> {
  fn clone(&self) -> Self {
    Self(self.0.clone())
  }
}

pub type SharedArrayBufferStore =
  CrossIsolateStore<v8::SharedRef<v8::BackingStore>>;

pub type CompiledWasmModuleStore = CrossIsolateStore<v8::CompiledWasmModule>;

/// Internal state for JsRuntime which is stored in one of v8::Isolate's
/// embedder slots.
pub struct JsRuntimeState {
  pub(crate) source_mapper: Rc<RefCell<SourceMapper>>,
  pub(crate) op_state: Rc<RefCell<OpState>>,
  pub(crate) shared_array_buffer_store: Option<SharedArrayBufferStore>,
  pub(crate) compiled_wasm_module_store: Option<CompiledWasmModuleStore>,
  wait_for_inspector_disconnect_callback:
    Option<WaitForInspectorDisconnectCallback>,
  pub(crate) validate_import_attributes_cb: Option<ValidateImportAttributesCb>,
  pub(crate) custom_module_evaluation_cb: Option<CustomModuleEvaluationCb>,
  pub(crate) vm_dynamic_import_callbacks:
    RefCell<HashMap<u32, v8::Global<v8::Function>>>,
  pub(crate) next_vm_dynamic_import_callback_id: Cell<u32>,
  /// Hook invoked by `host_initialize_import_meta_object_callback` when V8
  /// asks to initialize `import.meta` for a module that is *not* tracked by
  /// the module map. This is the path `node:vm` `SourceTextModule` takes:
  /// the v8::Module is created directly by the `node:vm` op and is never
  /// registered in the deno_core module map, but V8 still invokes the
  /// per-isolate import-meta callback for it. Without this hook the
  /// callback used to `panic!("Module not found")`.
  pub(crate) external_module_import_meta_cb:
    Cell<Option<ExternalModuleImportMetaCb>>,
  pub(crate) eval_context_get_code_cache_cb:
    RefCell<Option<EvalContextGetCodeCacheCb>>,
  pub(crate) eval_context_code_cache_ready_cb:
    RefCell<Option<EvalContextCodeCacheReadyCb>>,
  pub(crate) cppgc_template: RefCell<Option<v8::Global<v8::FunctionTemplate>>>,
  pub(crate) function_templates: Rc<RefCell<FunctionTemplateData>>,
  pub(crate) callsite_prototype: RefCell<Option<v8::Global<v8::Object>>>,
  waker: Arc<AtomicWaker>,
  /// Foreground V8 tasks queued by the custom platform. Shared with the
  /// global isolate registry so background threads can push tasks, while
  /// the event loop drains them without touching the global map.
  foreground_tasks: setup::ForegroundTaskQueue,
  /// Accessed through [`JsRuntimeState::with_inspector`].
  inspector: RefCell<Option<Rc<JsRuntimeInspector>>>,
  has_inspector: Cell<bool>,
  lazy_extensions: Vec<&'static str>,
  /// Counter for consecutive event loop iterations where module evaluation
  /// is pending but V8 reports no stalled top-level await. Used to detect
  /// deadlocks and avoid spinning the event loop indefinitely.
  tla_stall_retries: Cell<u32>,
}

#[derive(Default)]
pub struct RuntimeOptions {
  /// Implementation of `ModuleLoader` which will be
  /// called when V8 requests to load ES modules in the main realm.
  ///
  /// If not provided runtime will error if code being
  /// executed tries to load modules.
  pub module_loader: Option<Rc<dyn ModuleLoader>>,

  /// If specified, enables V8 code cache for extension code.
  pub extension_code_cache: Option<Rc<dyn ExtCodeCache>>,

  /// If specified, transpiles extensions before loading.
  pub extension_transpiler: Option<Rc<ExtensionTranspiler>>,

  /// Provide a function that may optionally provide a metrics collector
  /// for a given op.
  pub op_metrics_factory_fn: Option<OpMetricsFactoryFn>,

  /// JsRuntime extensions, not to be confused with ES modules.
  /// Only ops registered by extensions will be initialized. If you need
  /// to execute JS code from extensions, pass source files in `js` or `esm`
  /// option on `ExtensionBuilder`.
  ///
  /// If you are creating a runtime from a snapshot take care not to include
  /// JavaScript sources in the extensions.
  pub extensions: Vec<Extension>,

  /// V8 snapshot that should be loaded on startup.
  ///
  /// For testing, use `runtime.snapshot()` and then [`Box::leak`] to acquire
  // a static slice.
  pub startup_snapshot: Option<&'static [u8]>,

  /// Source for `lazy_loaded_js` files that were *not* consumed at snapshot
  /// build time and therefore aren't reachable via the snapshot blob. The
  /// build script that produced `startup_snapshot` emits this table.
  /// Each entry is `(specifier, source)`.
  pub residual_lazy_js_sources: &'static [(&'static str, &'static str)],

  /// Source for `lazy_loaded_esm` files that were *not* consumed at snapshot
  /// build time. See [`Self::residual_lazy_js_sources`].
  pub residual_lazy_esm_sources: &'static [(&'static str, &'static str)],

  /// Should op registration be skipped?
  pub skip_op_registration: bool,

  /// Isolate creation parameters.
  pub create_params: Option<v8::CreateParams>,

  /// V8 platform instance to use. Used when Deno initializes V8
  /// (which it only does once), otherwise it's silently dropped.
  pub v8_platform: Option<v8::SharedRef<v8::Platform>>,

  /// The store to use for transferring SharedArrayBuffers between isolates.
  /// If multiple isolates should have the possibility of sharing
  /// SharedArrayBuffers, they should use the same [SharedArrayBufferStore]. If
  /// no [SharedArrayBufferStore] is specified, SharedArrayBuffer can not be
  /// serialized.
  pub shared_array_buffer_store: Option<SharedArrayBufferStore>,

  /// The store to use for transferring `WebAssembly.Module` objects between
  /// isolates.
  /// If multiple isolates should have the possibility of sharing
  /// `WebAssembly.Module` objects, they should use the same
  /// [CompiledWasmModuleStore]. If no [CompiledWasmModuleStore] is specified,
  /// `WebAssembly.Module` objects cannot be serialized.
  pub compiled_wasm_module_store: Option<CompiledWasmModuleStore>,

  /// Start inspector instance to allow debuggers to connect.
  pub inspector: bool,

  /// Describe if this is the main runtime instance, used by debuggers in some
  /// situation - like disconnecting when program finishes running.
  pub is_main: bool,

  /// Worker ID for inspector context naming (e.g., "worker [1]", "worker [2]").
  /// Only used when `is_main` is false. Starts at 1.
  pub worker_id: Option<u32>,

  #[cfg(any(test, feature = "unsafe_runtime_options"))]
  /// Should this isolate expose the v8 natives (eg: %OptimizeFunctionOnNextCall) and
  /// GC control functions (`gc()`)? WARNING: This should not be used for production code as
  /// this may expose the runtime to security vulnerabilities.
  pub unsafe_expose_natives_and_gc: bool,

  /// A callback that can be used to validate import attributes received at
  /// the import site. If no callback is provided, all attributes are allowed.
  ///
  /// Embedders might use this callback to eg. validate value of "type"
  /// attribute, not allowing other types than "JSON".
  ///
  /// To signal validation failure, users should throw an V8 exception inside
  /// the callback.
  pub validate_import_attributes_cb: Option<ValidateImportAttributesCb>,

  /// A callback that is called when the event loop has no more work to do,
  /// but there are active, non-blocking inspector session (eg. Chrome
  /// DevTools inspector is connected). The embedder can use this callback
  /// to eg. print a message notifying user about program finished running.
  /// This callback can be called multiple times, eg. after the program finishes
  /// more work can be scheduled from the DevTools.
  pub wait_for_inspector_disconnect_callback:
    Option<WaitForInspectorDisconnectCallback>,

  /// A callback that allows to evaluate a custom type of a module - eg.
  /// embedders might implement loading WASM or test modules.
  pub custom_module_evaluation_cb: Option<CustomModuleEvaluationCb>,

  /// Callbacks to retrieve and store code cache for scripts evaluated
  /// through evalContext.
  pub eval_context_code_cache_cbs:
    Option<(EvalContextGetCodeCacheCb, EvalContextCodeCacheReadyCb)>,

  /// A callback to specify how stack traces should be used when an op is
  /// annotated with `stack_trace` attribute. Use wisely, as it's very expensive
  /// to collect stack traces on each op invocation.
  pub maybe_op_stack_trace_callback: Option<OpStackTraceCallback>,
}

impl RuntimeOptions {
  #[cfg(any(test, feature = "unsafe_runtime_options"))]
  fn unsafe_expose_natives_and_gc(&self) -> bool {
    self.unsafe_expose_natives_and_gc
  }

  #[cfg(not(any(test, feature = "unsafe_runtime_options")))]
  fn unsafe_expose_natives_and_gc(&self) -> bool {
    false
  }
}

#[derive(Copy, Clone, Debug, Default)]
pub struct PollEventLoopOptions {
  pub wait_for_inspector: bool,
}

#[derive(Default)]
pub struct CreateRealmOptions {
  /// Implementation of `ModuleLoader` which will be
  /// called when V8 requests to load ES modules in the realm.
  ///
  /// If not provided, there will be an error if code being
  /// executed tries to load modules from the realm.
  pub module_loader: Option<Rc<dyn ModuleLoader>>,
}

#[macro_export]
macro_rules! scope {
  ($scope: ident, $self: expr) => {
    let context = $self.main_context();
    let isolate = &mut *$self.v8_isolate();
    $crate::v8::scope!($scope, isolate);
    let context = $crate::v8::Local::new($scope, context);
    let $scope = &mut $crate::v8::ContextScope::new($scope, context);
  };
}

impl JsRuntime {
  /// Explicitly initalizes the V8 platform using the passed platform. This
  /// should only be called once per process. Further calls will be silently
  /// ignored.
  #[cfg(not(any(test, feature = "unsafe_runtime_options")))]
  pub fn init_platform(v8_platform: Option<v8::SharedRef<v8::Platform>>) {
    setup::init_v8(v8_platform, cfg!(test), false);
  }

  /// Explicitly initalizes the V8 platform using the passed platform. This
  /// should only be called once per process. Further calls will be silently
  /// ignored.
  ///
  /// The `expose_natives` flag is used to expose the v8 natives
  /// (eg: %OptimizeFunctionOnNextCall) and GC control functions (`gc()`).
  /// WARNING: This should not be used for production code as
  /// this may expose the runtime to security vulnerabilities.
  #[cfg(any(test, feature = "unsafe_runtime_options"))]
  pub fn init_platform(
    v8_platform: Option<v8::SharedRef<v8::Platform>>,
    expose_natives: bool,
  ) {
    setup::init_v8(v8_platform, cfg!(test), expose_natives);
  }

  /// Only constructor, configuration is done through `options`.
  /// Panics if the runtime cannot be initialized.
  pub fn new(options: RuntimeOptions) -> JsRuntime {
    match Self::try_new(options) {
      Ok(runtime) => runtime,
      Err(err) => {
        panic!(
          "Failed to initialize a JsRuntime: {}",
          err.print_with_cause()
        );
      }
    }
  }

  /// Only constructor, configuration is done through `options`.
  /// Returns an error if the runtime cannot be initialized.
  pub fn try_new(mut options: RuntimeOptions) -> Result<JsRuntime, CoreError> {
    let _t0 = startup_phase_begin();
    setup::init_v8(
      options.v8_platform.take(),
      cfg!(test),
      options.unsafe_expose_natives_and_gc(),
    );
    startup_phase_end(_t0, "init_v8");
    JsRuntime::new_inner(options, false)
  }

  pub(crate) fn state_from(isolate: &v8::Isolate) -> Rc<JsRuntimeState> {
    let state_ptr = isolate.get_data(STATE_DATA_OFFSET);
    let state_rc =
      // SAFETY: We are sure that it's a valid pointer for whole lifetime of
      // the runtime.
      unsafe { Rc::from_raw(state_ptr as *const JsRuntimeState) };
    let state = state_rc.clone();
    std::mem::forget(state_rc);
    state
  }

  /// Returns the `OpState` associated with the passed `Isolate`.
  pub fn op_state_from(isolate: &v8::Isolate) -> Rc<RefCell<OpState>> {
    let state = Self::state_from(isolate);
    state.op_state.clone()
  }

  pub(crate) fn has_more_work(scope: &mut v8::PinScope) -> bool {
    EventLoopPendingState::new_from_scope(scope).is_pending()
  }

  /// Returns the `OpMetadata` associated with the op `name`.
  /// Note this is linear with respect to the number of ops registered.
  pub fn op_metadata(&self, name: &str) -> Option<OpMetadata> {
    let state = &self.inner.main_realm.0.context_state;
    state.op_ctxs.iter().find_map(|ctx| {
      if ctx.decl.name == name {
        Some(ctx.decl.metadata)
      } else {
        None
      }
    })
  }

  fn new_inner(
    mut options: RuntimeOptions,
    will_snapshot: bool,
  ) -> Result<JsRuntime, CoreError> {
    let _phase_total = startup_phase_begin();
    let init_mode = InitMode::from_options(&options);
    let mut extensions = std::mem::take(&mut options.extensions);
    let mut isolate_allocations = IsolateAllocations::default();

    // `lazy_loaded_js` sources are externalized (and pre-wrapped) only when
    // building the snapshot, so consumed scripts bake in as clean external
    // sources. At runtime they stay as static registrations.
    let externalize_lazy_js = will_snapshot;

    let enable_stack_trace_in_ops =
      options.maybe_op_stack_trace_callback.is_some();

    // First let's create an `OpState` and contribute to it from extensions...
    let _phase = startup_phase_begin();
    let mut op_state = OpState::new(options.maybe_op_stack_trace_callback);
    let unrefed_ops = op_state.unrefed_ops.clone();

    let lazy_extensions =
      extension_set::setup_op_state(&mut op_state, &mut extensions);
    startup_phase_end(_phase, "setup_op_state");

    // Load the sources and source maps
    let mut files_loaded = Vec::with_capacity(128);
    let loader = options
      .module_loader
      .unwrap_or_else(|| Rc::new(NoopModuleLoader));

    let mut source_mapper = SourceMapper::new(loader.clone());

    let _phase = startup_phase_begin();
    let (maybe_startup_snapshot, mut sidecar_data) = options
      .startup_snapshot
      .take()
      .map(snapshot::deconstruct)
      .unzip();
    startup_phase_end(_phase, "snapshot::deconstruct");

    let _phase = startup_phase_begin();
    let mut sources = extension_set::into_sources_and_source_maps(
      options.extension_transpiler.as_deref(),
      &extensions,
      sidecar_data.as_ref().map(|s| &*s.snapshot_data.extensions),
      externalize_lazy_js,
      |source| {
        mark_as_loaded_from_fs_during_snapshot(&mut files_loaded, &source.code)
      },
    )?;
    startup_phase_end(_phase, "into_sources_and_source_maps");

    for loaded_source in sources
      .js
      .iter()
      .chain(sources.esm.iter())
      .chain(sources.lazy_esm.iter())
      .filter(|s| s.maybe_source_map.is_some())
    {
      source_mapper.add_ext_source_map(
        loaded_source.specifier.try_clone().unwrap(),
        loaded_source.maybe_source_map.clone().unwrap(),
      );
    }

    // ...now let's set up ` JsRuntimeState`, we'll need to set some fields
    // later, after `JsRuntime` is all set up...
    let waker = op_state.waker.clone();
    let op_state = Rc::new(RefCell::new(op_state));
    let (eval_context_get_code_cache_cb, eval_context_set_code_cache_cb) =
      options
        .eval_context_code_cache_cbs
        .map(|cbs| (Some(cbs.0), Some(cbs.1)))
        .unwrap_or_default();
    let state_rc = Rc::new(JsRuntimeState {
      source_mapper: Rc::new(RefCell::new(source_mapper)),
      shared_array_buffer_store: options.shared_array_buffer_store,
      compiled_wasm_module_store: options.compiled_wasm_module_store,
      wait_for_inspector_disconnect_callback: options
        .wait_for_inspector_disconnect_callback,
      op_state: op_state.clone(),
      validate_import_attributes_cb: options.validate_import_attributes_cb,
      custom_module_evaluation_cb: options.custom_module_evaluation_cb,
      vm_dynamic_import_callbacks: Default::default(),
      next_vm_dynamic_import_callback_id: Cell::new(1),
      external_module_import_meta_cb: Cell::new(None),
      eval_context_get_code_cache_cb: RefCell::new(
        eval_context_get_code_cache_cb,
      ),
      eval_context_code_cache_ready_cb: RefCell::new(
        eval_context_set_code_cache_cb,
      ),
      waker: waker.clone(),
      foreground_tasks: Default::default(),
      // Some fields are initialized later after isolate is created
      inspector: None.into(),
      has_inspector: false.into(),
      cppgc_template: None.into(),
      function_templates: Default::default(),
      callsite_prototype: None.into(),
      lazy_extensions,
      tla_stall_retries: Cell::new(0),
    });

    // ...now we're moving on to ops; set them up, create `OpCtx` for each op
    // and get ready to actually create V8 isolate...
    let (op_decls, mut op_method_decls) =
      extension_set::init_ops(crate::ops_builtin::BUILTIN_OPS, &mut extensions);

    let op_driver = Rc::new(OpDriverImpl::default());
    let op_metrics_factory_fn = options.op_metrics_factory_fn.take();

    let (mut op_ctxs, methods_ctx_offset) = extension_set::create_op_ctxs(
      op_decls,
      &mut op_method_decls,
      op_metrics_factory_fn,
      op_driver.clone(),
      op_state.clone(),
      state_rc.clone(),
      enable_stack_trace_in_ops,
    );

    // ...ops are now almost fully set up; let's create a V8 isolate...
    let (
      global_template_middleware,
      global_object_middlewares,
      additional_references,
    ) = extension_set::get_middlewares_and_external_refs(&mut extensions);

    // Capture the extension, op and source counts. `source_count` MUST mirror
    // the number of `v8::OneByteConst` external strings produced by
    // [`bindings::externalize_sources`] for the same `will_snapshot` value:
    // `js + esm + lazy_esm`, plus `lazy_loaded_js` only when building the
    // snapshot (where those scripts are externalized so consumed ones bake into
    // the snapshot as clean external sources). At runtime `lazy_loaded_js` is
    // not externalized here.
    let extensions = extensions.iter().map(|e| e.name).collect();
    let op_count = op_ctxs.len();
    let source_count = sources.js.len()
      + sources.esm.len()
      + sources.lazy_esm.len()
      + if externalize_lazy_js {
        sources.lazy_js.len()
      } else {
        0
      };
    let addl_refs_count = additional_references.len();

    let ops_in_snapshot = sidecar_data
      .as_ref()
      .map(|d| d.snapshot_data.op_count)
      .unwrap_or_default();
    let sources_in_snapshot = sidecar_data
      .as_ref()
      .map(|d| d.snapshot_data.source_count)
      .unwrap_or_default();

    let snapshot_sources: Vec<&[u8]> = sidecar_data
      .as_mut()
      .map(|s| std::mem::take(&mut s.snapshot_data.external_strings))
      .unwrap_or_default();
    (
      isolate_allocations.externalized_sources,
      isolate_allocations.original_sources,
      isolate_allocations.lazy_source_specifiers,
    ) = bindings::externalize_sources(
      &mut sources,
      snapshot_sources,
      externalize_lazy_js,
    );

    let external_references = bindings::create_external_references(
      &op_ctxs,
      &additional_references,
      &isolate_allocations.externalized_sources,
      ops_in_snapshot,
      sources_in_snapshot,
    );

    let has_snapshot = maybe_startup_snapshot.is_some();
    let _phase = startup_phase_begin();
    let mut isolate = setup::create_isolate(
      will_snapshot,
      options.create_params.take(),
      maybe_startup_snapshot,
      external_references.into(),
    );
    startup_phase_end(_phase, "create_isolate (v8 snapshot deser)");

    let isolate_ptr = unsafe { isolate.as_raw_isolate_ptr() };

    // Register this isolate in the global platform registry so V8 background
    // threads can queue foreground tasks. The task queue Arc is already shared
    // with JsRuntimeState (created above) so the event loop can drain it
    // without touching the global map.
    setup::register_isolate(
      setup::isolate_ptr_to_key(isolate_ptr),
      waker.clone(),
      tokio::runtime::Handle::try_current().ok(),
      state_rc.foreground_tasks.clone(),
    );

    // ...isolate is fully set up, we can forward its pointer to the ops to finish
    // their' setup...
    for op_ctx in op_ctxs.iter_mut() {
      op_ctx.isolate = isolate_ptr;
    }

    op_state.borrow_mut().put(isolate_ptr);

    // ...once ops and isolate are set up, we can create a `ContextState`...
    let context_state = Rc::new(ContextState::new(
      op_driver.clone(),
      isolate_ptr,
      op_ctxs,
      op_method_decls,
      methods_ctx_offset,
      op_state.borrow().external_ops_tracker.clone(),
      unrefed_ops,
    ));

    // TODO(bartlomieju): factor out
    // Add the task spawners to the OpState
    let spawner = context_state
      .task_spawner_factory
      .clone()
      .new_same_thread_spawner();
    op_state.borrow_mut().put(spawner);
    let spawner = context_state
      .task_spawner_factory
      .clone()
      .new_cross_thread_spawner();
    op_state.borrow_mut().put(spawner);

    // ...and with `ContextState` available we can set up V8 context...
    let _phase = startup_phase_begin();
    let mut snapshotted_data = None;
    let main_context = {
      v8::scope!(let scope, &mut isolate);

      let cppgc_template = crate::cppgc::make_cppgc_template(scope);
      state_rc
        .cppgc_template
        .borrow_mut()
        .replace(v8::Global::new(scope, cppgc_template));

      let _p_ctx = startup_phase_begin();
      let context = create_context(
        scope,
        &global_template_middleware,
        &global_object_middlewares,
        has_snapshot,
      );
      startup_phase_end(_p_ctx, "  V8 Context::from_snapshot");

      // Get module map data from the snapshot
      if let Some(raw_data) = sidecar_data {
        let _p_ld = startup_phase_begin();
        snapshotted_data = Some(snapshot::load_snapshotted_data_from_snapshot(
          scope, context, raw_data,
        ));
        startup_phase_end(_p_ld, "  load_data loop (get_context_data x N)");
      }

      v8::Global::new(scope, context)
    };
    startup_phase_end(_phase, "create_context+load_data");

    let main_realm = {
      v8::scope_with_context!(context_scope, &mut isolate, &main_context);
      let scope = context_scope;
      let context = v8::Local::new(scope, &main_context);

      let callsite_prototype = crate::error::make_callsite_prototype(scope);
      state_rc
        .callsite_prototype
        .borrow_mut()
        .replace(v8::Global::new(scope, callsite_prototype));

      // ...followed by creation of `Deno.core` namespace, as well as internal
      // infrastructure to provide JavaScript bindings for ops...
      let _phase = startup_phase_begin();
      if init_mode == InitMode::New {
        bindings::initialize_deno_core_namespace(scope, context, init_mode);
        bindings::initialize_primordials_and_infra(scope)?;
      }
      // If we're creating a new runtime or there are new ops to register
      // set up JavaScript bindings for them.
      if init_mode.needs_ops_bindings() {
        bindings::initialize_deno_core_ops_bindings(
          scope,
          context,
          &context_state.op_ctxs,
          &context_state.op_method_decls,
          methods_ctx_offset,
          &mut state_rc.function_templates.borrow_mut(),
          will_snapshot,
        );
      } else if !will_snapshot {
        // Snapshots built against V8 14.9+ bake the slow version of each op
        // function (see `op_ctx_template`); the fast-call overloads must be
        // re-attached at runtime. That pass (~0.9ms, ~1.6k V8 functions) only
        // helps ops accessed at runtime — baked modules already captured their
        // slow refs at snapshot eval — so we DEFER it until the first residual
        // ext-module load (`ensure_fast_ops_upgraded`). A program that loads no
        // residual module (e.g. an empty script) never pays for it.
        //
        // Capture the refs the deferred upgrade needs NOW, while `Deno.core` is
        // still on the global — it's scrubbed from the public `Deno` after
        // bootstrap, so the post-bootstrap deferred caller can't read them.
        let (ops_obj, stub_fn) =
          bindings::snapshotted_fast_op_refs(scope, context);
        *context_state.deferred_fast_ops.borrow_mut() = Some((
          v8::Global::new(scope, ops_obj),
          v8::Global::new(scope, stub_fn),
        ));
      }
      // The deferred upgrade applies ONLY when loading a snapshot at runtime.
      // In the fresh-bind path the ops were just bound with fast calls, and in
      // the snapshot-build path we must keep the slow ops (fast-call functions
      // can't be serialized) and must NOT upgrade even though `op_load_ext_script`
      // runs during the build. Mark those paths done so `ensure_fast_ops_upgraded`
      // is a no-op for them.
      if init_mode.needs_ops_bindings() || will_snapshot {
        context_state.fast_ops_upgraded.set(true);
      }
      startup_phase_end(_phase, "ops_bindings (fast call upgrade)");

      // SAFETY: Initialize the context state slot.
      unsafe {
        context.set_aligned_pointer_in_embedder_data(
          super::jsrealm::CONTEXT_STATE_SLOT_INDEX,
          Rc::into_raw(context_state.clone()) as *mut c_void,
        );
      }

      let inspector = if options.inspector {
        Some(JsRuntimeInspector::new(
          isolate_ptr,
          scope,
          context,
          options.is_main,
          options.worker_id,
        ))
      } else {
        None
      };

      // ...now that JavaScript bindings to ops are available we can deserialize
      // modules stored in the snapshot (because they depend on the ops and external
      // references must match properly) and recreate a module map...
      let exception_state = context_state.exception_state.clone();
      let module_map = Rc::new(ModuleMap::new(
        loader,
        state_rc.source_mapper.clone(),
        exception_state.clone(),
        will_snapshot,
      ));

      let _phase = startup_phase_begin();
      if let Some((snapshotted_data, mut data_store)) = snapshotted_data {
        *exception_state.js_handled_promise_rejection_cb.borrow_mut() =
          snapshotted_data
            .js_handled_promise_rejection_cb
            .map(|cb| data_store.get(scope, cb));
        module_map.update_with_snapshotted_data(
          scope,
          &mut data_store,
          snapshotted_data.module_map_data,
        );

        if let Some(index) = snapshotted_data.ext_import_meta_proto {
          *context_state.ext_import_meta_proto.borrow_mut() =
            Some(data_store.get(scope, index));
        }

        state_rc
          .function_templates
          .borrow_mut()
          .update_with_snapshotted_data(
            scope,
            &mut data_store,
            snapshotted_data.function_templates_data,
          );

        let mut mapper = state_rc.source_mapper.borrow_mut();
        for (key, map) in snapshotted_data.ext_source_maps {
          mapper.add_ext_source_map(ModuleName::from_static(key), map.into());
        }
      }
      startup_phase_end(_phase, "load module map from snapshot");

      if context_state.ext_import_meta_proto.borrow().is_none() {
        let null = v8::null(scope);
        let obj = v8::Object::with_prototype_and_properties(
          scope,
          null.into(),
          &[],
          &[],
        );
        *context_state.ext_import_meta_proto.borrow_mut() =
          Some(v8::Global::new(scope, obj));
      }

      // SAFETY: Set the module map slot in the context
      unsafe {
        context.set_aligned_pointer_in_embedder_data(
          super::jsrealm::MODULE_MAP_SLOT_INDEX,
          Rc::into_raw(module_map.clone()) as *mut c_void,
        );
      }

      // ...we are ready to create a "realm" for the context...
      let main_realm = {
        let main_realm = JsRealmInner::new(
          context_state,
          main_context,
          module_map.clone(),
          state_rc.function_templates.clone(),
        );
        // TODO(bartlomieju): why is this done in here? Maybe we can hoist it out?
        state_rc.has_inspector.set(inspector.is_some());
        *state_rc.inspector.borrow_mut() = inspector;
        main_realm
      };
      let main_realm = JsRealm::new(main_realm);
      scope.set_data(
        STATE_DATA_OFFSET,
        Rc::into_raw(state_rc.clone()) as *mut c_void,
      );
      main_realm
    };

    // ...which allows us to create the `JsRuntime` instance...
    let mut js_runtime = JsRuntime {
      inner: InnerIsolateState {
        will_snapshot,
        op_count,
        extensions,
        source_count,
        addl_refs_count,
        main_realm: ManuallyDrop::new(main_realm),
        state: ManuallyDropRc(ManuallyDrop::new(state_rc)),
        v8_isolate: ManuallyDrop::new(isolate),
      },
      allocations: isolate_allocations,
      files_loaded_from_fs_during_snapshot: vec![],
      is_main_runtime: options.is_main,
    };

    // ...we're almost done with the setup, all that's left is to execute
    // internal JS and then execute code provided by extensions...
    {
      let realm = JsRealm::clone(&js_runtime.inner.main_realm);
      let context_global = realm.context();
      let module_map = realm.0.module_map();

      // TODO(bartlomieju): this is somewhat duplicated in `bindings::initialize_context`,
      // but for migration period we need to have ops available in both `Deno.core.ops`
      // as well as have them available in "virtual ops module"
      // if !matches!(
      //   self.init_mode,
      //   InitMode::FromSnapshot {
      //     skip_op_registration: true
      //   }
      // ) {
      if init_mode == InitMode::New {
        let _phase = startup_phase_begin();
        js_runtime
          .execute_virtual_ops_module(context_global, module_map.clone());
        startup_phase_end(_phase, "execute_virtual_ops_module");
      }

      if init_mode == InitMode::New {
        let _phase = startup_phase_begin();
        js_runtime.execute_builtin_sources(
          &realm,
          &module_map,
          &mut files_loaded,
        )?;
        startup_phase_end(_phase, "execute_builtin_sources");
      }

      let _phase = startup_phase_begin();
      js_runtime.store_js_callbacks(&realm, will_snapshot);
      startup_phase_end(_phase, "store_js_callbacks");

      // Register residual `lazy_loaded_*` sources from the snapshot bundle.
      // These are the files that were declared on extensions but were not
      // consumed at snapshot build time, so the snapshot blob doesn't carry
      // them and `core.loadExtScript()` / lazy ESM imports need to find them
      // here. (When there is no snapshot, the same sources are loaded from
      // disk through `Extension.lazy_loaded_*_files` instead.)
      module_map.add_residual_lazy_loaded_sources(
        options.residual_lazy_js_sources,
        options.residual_lazy_esm_sources,
      );

      let _phase = startup_phase_begin();
      js_runtime.init_extension_js(
        &realm,
        &module_map,
        sources,
        options.extension_code_cache,
      )?;
      startup_phase_end(_phase, "init_extension_js");
    }

    startup_phase_end(_phase_total, "TOTAL JsRuntime::new_inner");

    if will_snapshot {
      js_runtime.files_loaded_from_fs_during_snapshot = files_loaded;
    }

    // Every runtime gets a uv loop for the libuv compat layer (timers,
    // I/O, setImmediate, etc.). Stored in both OpState (for ext/node ops
    // that need the raw pointer) and ContextState (for event loop phases).
    if !will_snapshot {
      // SAFETY: zeroed memory is valid for uv_loop_t before uv_loop_init.
      let mut uv_loop =
        Box::new(unsafe { std::mem::zeroed::<uv_compat::UvLoop>() });
      // SAFETY: uv_loop points to valid zeroed memory.
      unsafe { uv_compat::uv_loop_init(&mut *uv_loop) };
      let loop_ptr: *mut uv_compat::UvLoop = &mut *uv_loop;
      // SAFETY: loop_ptr is valid and initialized.
      unsafe { js_runtime.register_uv_loop(loop_ptr) };
      js_runtime.inner.state.op_state.borrow_mut().put(uv_loop);
      js_runtime
        .inner
        .state
        .op_state
        .borrow_mut()
        .put(uv_compat::AsyncId::default());
    }

    // ...and we've made it; `JsRuntime` is ready to execute user code.
    Ok(js_runtime)
  }

  /// If extensions were initialized with `lazy_init`, they need to be
  /// fully initialized with this method.
  pub fn lazy_init_extensions(
    &self,
    ext_args: Vec<ExtensionArguments>,
  ) -> Result<(), CoreError> {
    if ext_args.len() != self.inner.state.lazy_extensions.len() {
      return Err(
        CoreErrorKind::ExtensionLazyInitCountMismatch(
          ExtensionLazyInitCountMismatchError {
            lazy_init_extensions_len: self.inner.state.lazy_extensions.len(),
            arguments_len: ext_args.len(),
          },
        )
        .into_box(),
      );
    }

    let mut state = self.inner.state.op_state.borrow_mut();

    for (mut args, expected_name) in ext_args
      .into_iter()
      .zip(self.inner.state.lazy_extensions.iter())
    {
      if args.name != *expected_name {
        return Err(
          CoreErrorKind::ExtensionLazyInitOrderMismatch(
            ExtensionLazyInitOrderMismatchError {
              expected: expected_name,
              actual: args.name,
            },
          )
          .into_box(),
        );
      }

      let Some(f) = args.op_state_fn.take() else {
        continue;
      };

      f(&mut state);
    }

    Ok(())
  }

  pub fn set_eval_context_code_cache_cbs(
    &self,
    eval_context_code_cache_cbs: Option<(
      EvalContextGetCodeCacheCb,
      EvalContextCodeCacheReadyCb,
    )>,
  ) {
    let (eval_context_get_code_cache_cb, eval_context_set_code_cache_cb) =
      eval_context_code_cache_cbs
        .map(|cbs| (Some(cbs.0), Some(cbs.1)))
        .unwrap_or_default();
    *self.inner.state.eval_context_get_code_cache_cb.borrow_mut() =
      eval_context_get_code_cache_cb;
    *self
      .inner
      .state
      .eval_context_code_cache_ready_cb
      .borrow_mut() = eval_context_set_code_cache_cb;
  }

  #[cfg(test)]
  #[inline]
  pub(crate) fn module_map(&self) -> Rc<ModuleMap> {
    self.inner.main_realm.0.module_map()
  }

  #[inline]
  pub fn main_context(&self) -> v8::Global<v8::Context> {
    self.inner.main_realm.0.context().clone()
  }

  #[cfg(test)]
  pub(crate) fn main_realm(&self) -> JsRealm {
    JsRealm::clone(&self.inner.main_realm)
  }

  #[inline]
  pub fn v8_isolate(&mut self) -> &mut v8::OwnedIsolate {
    &mut self.inner.v8_isolate
  }

  #[inline]
  fn v8_isolate_ptr(&mut self) -> v8::UnsafeRawIsolatePtr {
    unsafe { self.inner.v8_isolate.as_raw_isolate_ptr() }
  }

  #[inline]
  pub fn inspector(&self) -> Rc<JsRuntimeInspector> {
    self.inner.state.inspector()
  }

  #[inline]
  pub fn wait_for_inspector_disconnect(&self) {
    if let Some(callback) = self
      .inner
      .state
      .wait_for_inspector_disconnect_callback
      .as_ref()
    {
      callback();
    }
  }

  pub fn runtime_activity_stats_factory(&self) -> RuntimeActivityStatsFactory {
    RuntimeActivityStatsFactory {
      context_state: self.inner.main_realm.0.context_state.clone(),
      op_state: self.inner.state.op_state.clone(),
    }
  }

  // TODO(bartlomieju): remove, instead `JsRuntimeForSnapshot::new` should return
  // a struct that contains this data.
  pub(crate) fn files_loaded_from_fs_during_snapshot(&self) -> &[&'static str] {
    &self.files_loaded_from_fs_during_snapshot
  }

  /// Returns the specifiers of every `lazy_loaded_esm` / `lazy_loaded_js` file
  /// whose source was compiled into the V8 snapshot during snapshot creation.
  pub(crate) fn consumed_lazy_specifiers(&self) -> Vec<String> {
    let module_map = self.inner.main_realm.0.module_map();
    let data = module_map.get_data().borrow();
    let mut set: Vec<String> = data
      .consumed_lazy_specifiers
      .borrow()
      .iter()
      .cloned()
      .collect();
    set.sort();
    set
  }

  /// Create a synthetic module - `ext:core/ops` - that exports all ops registered
  /// with the runtime.
  fn execute_virtual_ops_module(
    &mut self,
    context_global: &v8::Global<v8::Context>,
    module_map: Rc<ModuleMap>,
  ) {
    scope!(scope, self);
    let context_local = v8::Local::new(scope, context_global);
    let context_state = JsRealm::state_from_scope(scope);
    let global = context_local.global(scope);
    let synthetic_module_exports = create_exports_for_ops_virtual_module(
      &context_state.op_ctxs,
      &context_state.op_method_decls,
      context_state.methods_ctx_offset,
      scope,
      global,
    );
    let mod_id = module_map.new_synthetic_module(
      scope,
      VIRTUAL_OPS_MODULE_NAME,
      crate::ModuleType::JavaScript,
      synthetic_module_exports,
    );
    module_map.mod_evaluate_sync(scope, mod_id).unwrap();
  }

  /// Executes built-in scripts and ES modules - this code is required for
  /// ops system to work properly, as well as providing necessary bindings
  /// on the `Deno.core` namespace.
  ///
  /// This is not done in [`bindings::initialize_primordials_and_infra`] because
  /// some of this code already relies on certain ops being available.
  fn execute_builtin_sources(
    &mut self,
    _realm: &JsRealm,
    module_map: &Rc<ModuleMap>,
    files_loaded: &mut Vec<&'static str>,
  ) -> Result<(), CoreError> {
    scope!(scope, self);

    for source_file in &BUILTIN_SOURCES {
      let name = source_file.specifier.v8_string(scope).unwrap();
      let source = source_file.source.v8_string(scope).unwrap();

      let origin = script_origin(scope, name, false, None);
      let script = v8::Script::compile(scope, source, Some(&origin))
        .ok_or(CoreModuleParseError(source_file.specifier))?;
      script
        .run(scope)
        .ok_or(CoreModuleExecuteError(source_file.specifier))?;
    }

    for file_source in &BUILTIN_ES_MODULES {
      mark_as_loaded_from_fs_during_snapshot(files_loaded, &file_source.code);
      module_map.lazy_load_es_module_with_code(
        scope,
        file_source.specifier,
        file_source.load()?,
        None,
      )?;
    }

    Ok(())
  }

  /// Initializes JS of provided Extensions in the given realm.
  async fn init_extension_js_inner(
    &mut self,
    realm: &JsRealm,
    module_map: &Rc<ModuleMap>,
    loaded_sources: LoadedSources,
    ext_code_cache: Option<Rc<dyn ExtCodeCache>>,
  ) -> Result<(), CoreError> {
    // First, add all the lazy ESM
    for source in loaded_sources.lazy_esm {
      module_map.add_lazy_loaded_esm_source(source.specifier, source.code);
    }

    // Add lazy-loaded scripts (loaded on demand via loadExtScript())
    for source in loaded_sources.lazy_js {
      module_map.add_lazy_loaded_script_source(source.specifier, source.code);
    }

    // Register `synthetic_esm` mappings so imports of the declared module
    // specifiers resolve via the synthetic-module dispatch in
    // `resolve_callback` instead of going through normal ESM loading.
    for (module_spec, backing_spec) in loaded_sources.synthetic_esm {
      module_map.add_synthetic_esm_module(module_spec, backing_spec);
    }

    // Temporarily override the loader of the `ModuleMap` so we can load
    // extension code.

    // TODO(bartlomieju): maybe this should be a method on the `ModuleMap`,
    // instead of explicitly changing the `.loader` field?
    let loader = module_map.loader.borrow().clone();
    let mut modules = Vec::with_capacity(loaded_sources.esm.len());
    let mut sources = Vec::with_capacity(loaded_sources.esm.len());
    for esm in loaded_sources.esm {
      modules.push(ModuleSpecifier::parse(&esm.specifier).unwrap());
      sources.push((esm.specifier, esm.code));
    }
    let ext_loader =
      Rc::new(ExtModuleLoader::new(sources, ext_code_cache.clone()));
    *module_map.loader.borrow_mut() = ext_loader.clone();
    module_map.set_loading_internal_modules(true);

    // Next, load the extension modules as side modules (but do not execute them)
    for module in modules {
      // eprintln!("loading module: {module}");
      realm
        .load_side_es_module_from_code(self.v8_isolate(), module.into(), None)
        .await?;
    }

    // Execute extension scripts
    for source in loaded_sources.js {
      match &ext_code_cache {
        Some(ext_code_cache) => {
          let specifier = ModuleSpecifier::parse(&source.specifier)?;
          realm.execute_script_with_cache(
            self.v8_isolate(),
            specifier,
            source.code,
            &|specifier, code| {
              ext_code_cache.get_code_cache_info(specifier, code, false)
            },
            &|specifier, hash, code_cache| {
              ext_code_cache
                .code_cache_ready(specifier, hash, code_cache, false)
            },
          )?;
        }
        _ => {
          realm.execute_script(
            self.v8_isolate(),
            source.specifier,
            source.code,
          )?;
        }
      }
    }

    // ...then execute all entry points
    for specifier in loaded_sources.esm_entry_points {
      let Some(mod_id) =
        module_map.get_id(&specifier, RequestedModuleType::None)
      else {
        return Err(
          CoreErrorKind::MissingFromModuleMap(specifier.to_string()).into_box(),
        );
      };

      let isolate = self.v8_isolate();
      jsrealm::context_scope!(scope, realm, isolate);
      module_map.mod_evaluate_sync(scope, mod_id)?;
      let mut cx = Context::from_waker(Waker::noop());
      // poll once so code cache is populated. the `ExtCodeCache` trait is sync, so
      // the `CodeCacheReady` futures will always finish on the first poll.
      let _ = module_map.poll_progress(&mut cx, scope);
    }

    #[cfg(debug_assertions)]
    {
      jsrealm::context_scope!(scope, realm, self.v8_isolate());
      module_map.check_all_modules_evaluated(scope)?;
    }

    let module_map = realm.0.module_map();
    module_map.set_loading_internal_modules(false);
    *module_map.loader.borrow_mut() = loader;
    ext_loader.finalize()?;

    Ok(())
  }

  /// Initializes JS of provided Extensions in the given realm.
  fn init_extension_js(
    &mut self,
    realm: &JsRealm,
    module_map: &Rc<ModuleMap>,
    loaded_sources: LoadedSources,
    ext_code_cache: Option<Rc<dyn ExtCodeCache>>,
  ) -> Result<(), CoreError> {
    futures::executor::block_on(self.init_extension_js_inner(
      realm,
      module_map,
      loaded_sources,
      ext_code_cache,
    ))?;

    Ok(())
  }

  pub fn eval<'s, 'i, T>(
    scope: &mut v8::PinScope<'s, 'i>,
    code: &str,
  ) -> Option<v8::Local<'s, T>>
  where
    v8::Local<'s, T>: TryFrom<v8::Local<'s, v8::Value>, Error = v8::DataError>,
  {
    v8::escapable_handle_scope!(let scope, scope);
    let source = v8::String::new(scope, code).unwrap();
    let script = v8::Script::compile(scope, source, None).unwrap();
    let v = script.run(scope)?;
    scope.escape(v).try_into().ok()
  }

  /// Grab and store JavaScript bindings to callbacks necessary for the
  /// JsRuntime to operate properly.
  fn store_js_callbacks(&mut self, realm: &JsRealm, will_snapshot: bool) {
    let (
      event_loop_tick_cb,
      process_timers_cb,
      drain_next_tick_and_macrotasks_cb,
      handle_rejections_cb,
      build_custom_error_cb,
      error_constructors,
      run_immediate_callbacks_cb,
      wasm_instance_fn,
      wasm_instances_map,
    ) = {
      scope!(scope, self);
      let context = realm.context();
      let context_local = v8::Local::new(scope, context);
      let global = context_local.global(scope);
      let deno_obj: v8::Local<v8::Object> =
        bindings::get(scope, global, DENO, "Deno");
      let core_obj: v8::Local<v8::Object> =
        bindings::get(scope, deno_obj, CORE, "Deno.core");

      let event_loop_tick_cb: v8::Local<v8::Function> = bindings::get(
        scope,
        core_obj,
        EVENT_LOOP_TICK,
        "Deno.core.__eventLoopTick",
      );
      let process_timers_cb: v8::Local<v8::Function> = bindings::get(
        scope,
        core_obj,
        PROCESS_TIMERS,
        "Deno.core.__processTimers",
      );
      let drain_next_tick_and_macrotasks_cb: v8::Local<v8::Function> =
        bindings::get(
          scope,
          core_obj,
          DRAIN_NEXT_TICK_AND_MACROTASKS,
          "Deno.core.__drainNextTickAndMacrotasks",
        );
      let handle_rejections_cb: v8::Local<v8::Function> = bindings::get(
        scope,
        core_obj,
        HANDLE_REJECTIONS,
        "Deno.core.__handleRejections",
      );
      let build_custom_error_cb: v8::Local<v8::Function> = bindings::get(
        scope,
        core_obj,
        BUILD_CUSTOM_ERROR,
        "Deno.core.buildCustomError",
      );
      let error_constructors: v8::Local<v8::Object> = bindings::get(
        scope,
        core_obj,
        ERROR_CONSTRUCTORS,
        "Deno.core.errorConstructors",
      );
      let run_immediate_callbacks_cb: v8::Local<v8::Function> = bindings::get(
        scope,
        core_obj,
        RUN_IMMEDIATE_CALLBACKS,
        "Deno.core.runImmediateCallbacks",
      );
      let mut wasm_instance_fn = None;
      let mut wasm_instances_map = None;
      if !will_snapshot {
        let key = WEBASSEMBLY.v8_string(scope).unwrap();
        if let Some(web_assembly_obj_value) = global.get(scope, key.into()) {
          let maybe_web_assembly_object =
            TryInto::<v8::Local<v8::Object>>::try_into(web_assembly_obj_value);
          if let Ok(web_assembly_object) = maybe_web_assembly_object {
            wasm_instance_fn = Some(bindings::get::<v8::Local<v8::Function>>(
              scope,
              web_assembly_object,
              INSTANCE,
              "WebAssembly.Instance",
            ));
            // Registry mapping a Wasm module's namespace to its instance
            // exports, shared by all synthetic `.wasm` modules in this realm
            // via `import.meta.wasmInstances`. See `ContextState` for details.
            let weak_map_fn = bindings::get::<v8::Local<v8::Function>>(
              scope, global, WEAK_MAP, "WeakMap",
            );
            wasm_instances_map = weak_map_fn.new_instance(scope, &[]);
          }
        }
      }

      // SAFETY: The backing memory lives on ContextState which outlives
      // all JS. We pass a no-op destructor since ContextState owns
      // the memory.
      extern "C" fn _no_op_deleter(
        _data: *mut std::ffi::c_void,
        _len: usize,
        _deleter_data: *mut std::ffi::c_void,
      ) {
      }

      // Create a shared Uint8Array backed by ContextState::tick_info and
      // pass it to JS via __setTickInfo so JS can read/write
      // hasTickScheduled without crossing the JS-to-Rust boundary.
      {
        let state_rc = realm.0.state();
        let tick_info_ptr =
          state_rc.tick_info.as_ptr() as *mut std::ffi::c_void;
        let backing_store = unsafe {
          v8::ArrayBuffer::new_backing_store_from_ptr(
            tick_info_ptr,
            2,
            _no_op_deleter,
            std::ptr::null_mut(),
          )
        };
        let backing_store_shared = backing_store.make_shared();
        let ab =
          v8::ArrayBuffer::with_backing_store(scope, &backing_store_shared);
        let tick_info_array = v8::Uint8Array::new(scope, ab, 0, 2).unwrap();
        let set_tick_info_fn: v8::Local<v8::Function> = bindings::get(
          scope,
          core_obj,
          SET_TICK_INFO,
          "Deno.core.__setTickInfo",
        );
        let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();
        set_tick_info_fn.call(scope, undefined, &[tick_info_array.into()]);
        // Clean up the init-only setter from Deno.core
        let key = SET_TICK_INFO.v8_string(scope).unwrap();
        core_obj.delete(scope, key.into());
      }

      // Create a shared Uint32Array backed by ContextState::immediate_info
      // and pass it to JS via __setImmediateInfo.
      {
        let state_rc = realm.0.state();
        let imm_info_ptr =
          state_rc.immediate_info.as_ptr() as *mut std::ffi::c_void;
        let imm_byte_len = 3 * std::mem::size_of::<u32>();
        let backing_store = unsafe {
          v8::ArrayBuffer::new_backing_store_from_ptr(
            imm_info_ptr,
            imm_byte_len,
            _no_op_deleter,
            std::ptr::null_mut(),
          )
        };
        let backing_store_shared = backing_store.make_shared();
        let ab =
          v8::ArrayBuffer::with_backing_store(scope, &backing_store_shared);
        let imm_info_array = v8::Uint32Array::new(scope, ab, 0, 3).unwrap();
        let set_imm_info_fn: v8::Local<v8::Function> = bindings::get(
          scope,
          core_obj,
          SET_IMMEDIATE_INFO,
          "Deno.core.__setImmediateInfo",
        );
        let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();
        set_imm_info_fn.call(scope, undefined, &[imm_info_array.into()]);
        let key = SET_IMMEDIATE_INFO.v8_string(scope).unwrap();
        core_obj.delete(scope, key.into());
      }

      // Create a shared Int32Array backed by ContextState::timer_info
      // and pass it to JS via __setTimerInfo.
      {
        let state_rc = realm.0.state();
        let timer_info_ptr =
          state_rc.timer_info.as_ptr() as *mut std::ffi::c_void;
        let timer_byte_len = std::mem::size_of::<i32>();
        let backing_store = unsafe {
          v8::ArrayBuffer::new_backing_store_from_ptr(
            timer_info_ptr,
            timer_byte_len,
            _no_op_deleter,
            std::ptr::null_mut(),
          )
        };
        let backing_store_shared = backing_store.make_shared();
        let ab =
          v8::ArrayBuffer::with_backing_store(scope, &backing_store_shared);
        let timer_info_array = v8::Int32Array::new(scope, ab, 0, 1).unwrap();
        let set_timer_info_fn: v8::Local<v8::Function> = bindings::get(
          scope,
          core_obj,
          SET_TIMER_INFO,
          "Deno.core.__setTimerInfo",
        );
        let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();
        set_timer_info_fn.call(scope, undefined, &[timer_info_array.into()]);
        let key = SET_TIMER_INFO.v8_string(scope).unwrap();
        core_obj.delete(scope, key.into());
      }

      (
        v8::Global::new(scope, event_loop_tick_cb),
        v8::Global::new(scope, process_timers_cb),
        v8::Global::new(scope, drain_next_tick_and_macrotasks_cb),
        v8::Global::new(scope, handle_rejections_cb),
        v8::Global::new(scope, build_custom_error_cb),
        v8::Global::new(scope, error_constructors),
        v8::Global::new(scope, run_immediate_callbacks_cb),
        wasm_instance_fn.map(|f| v8::Global::new(scope, f)),
        wasm_instances_map.map(|m| v8::Global::new(scope, m)),
      )
    };

    // Put global handles in the realm's ContextState
    let state_rc = realm.0.state();
    state_rc
      .js_event_loop_tick_cb
      .borrow_mut()
      .replace(event_loop_tick_cb);
    state_rc
      .js_process_timers_cb
      .borrow_mut()
      .replace(process_timers_cb);
    state_rc
      .js_drain_next_tick_and_macrotasks_cb
      .borrow_mut()
      .replace(drain_next_tick_and_macrotasks_cb);
    state_rc
      .js_handle_rejections_cb
      .borrow_mut()
      .replace(handle_rejections_cb);
    state_rc
      .exception_state
      .js_build_custom_error_cb
      .borrow_mut()
      .replace(build_custom_error_cb);
    state_rc
      .exception_state
      .js_error_constructors
      .borrow_mut()
      .replace(error_constructors);
    state_rc
      .run_immediate_callbacks_cb
      .borrow_mut()
      .replace(run_immediate_callbacks_cb);
    if let Some(wasm_instance_fn) = wasm_instance_fn {
      state_rc
        .wasm_instance_fn
        .borrow_mut()
        .replace(wasm_instance_fn);
    }
    if let Some(wasm_instances_map) = wasm_instances_map {
      state_rc
        .wasm_instances_map
        .borrow_mut()
        .replace(wasm_instances_map);
    }
  }

  /// Returns the runtime's op state, which can be used to maintain ops
  /// and access resources between op calls.
  pub fn op_state(&self) -> Rc<RefCell<OpState>> {
    self.inner.state.op_state.clone()
  }

  /// Returns the raw `uv_loop_t` pointer registered with this runtime,
  /// or `None` if no loop is registered.
  pub fn uv_loop_ptr(&self) -> Option<*mut uv_compat::uv_loop_t> {
    self.inner.main_realm.0.context_state.uv_loop_ptr.get()
  }

  /// Returns the runtime's source mapper, which can be used to apply
  /// source maps to file locations.
  pub fn source_mapper(&self) -> Rc<RefCell<crate::source_map::SourceMapper>> {
    self.inner.state.source_mapper.clone()
  }

  /// Register a `uv_loop_t` with the runtime so that its event loop phases
  /// (timers, I/O, idle, prepare, check, close) are driven by
  /// `poll_event_loop`.
  ///
  /// A `v8::Global<v8::Context>` is created via `Global::into_raw()` and
  /// stored in `loop_.data` so that libuv-style callbacks can retrieve
  /// the context. The raw Global is dropped during realm cleanup.
  ///
  /// # Safety
  /// `loop_ptr` must be a valid, initialized `uv_loop_t` pointer that
  /// outlives the runtime.
  pub unsafe fn register_uv_loop(
    &mut self,
    loop_ptr: *mut uv_compat::uv_loop_t,
  ) {
    let realm = &self.inner.main_realm;
    let context_state = &realm.0.context_state;
    let inner_ptr = unsafe { uv_compat::uv_loop_get_inner_ptr(loop_ptr) };
    let uv_inner = inner_ptr as *const uv_compat::UvLoopInner;
    context_state.uv_loop_inner.set(Some(uv_inner));
    context_state.uv_loop_ptr.set(Some(loop_ptr));

    let global_ctx = realm.0.context().clone();
    let raw = global_ctx.into_raw();
    // SAFETY: `loop_ptr` is a valid, initialized `uv_loop_t` guaranteed
    // by the caller. `raw` is a persistent-handle slot pointer from
    // `Global::into_raw()` — V8 keeps it updated across GC cycles.
    // The raw Global is reconstructed and dropped in `JsRealmInner::destroy`.
    unsafe {
      (*loop_ptr).data = raw.as_ptr() as *mut std::ffi::c_void;
    }

    // Create the check handle for setImmediate.
    // JS controls start/stop/ref/unref via op_immediate_check.
    // SAFETY: loop_ptr is valid per caller contract.
    let check_handle =
      unsafe { uv_compat::ImmediateCheckHandle::new(loop_ptr) };
    *context_state.immediate_check_handle.borrow_mut() = Some(check_handle);
  }

  /// Returns the runtime's op names, ordered by OpId.
  pub fn op_names(&self) -> Vec<&'static str> {
    let state = &self.inner.main_realm.0.context_state;
    state.op_ctxs.iter().map(|o| o.decl.name).collect()
  }

  /// Executes traditional, non-ECMAScript-module JavaScript code, This code executes in
  /// the global scope by default, and it is possible to maintain local JS state and invoke
  /// this method multiple times.
  ///
  /// `name` may be any type that implements the internal [`IntoModuleName`] trait.
  /// It can be a filepath or any other string, but it is required to be 7-bit ASCII, eg.
  ///
  ///   - "/some/file/path.js"
  ///   - "<anon>"
  ///   - "[native code]"
  ///
  /// The same `name` value can be used for multiple executions.
  ///
  /// The source may be any type that implements the internal [`IntoModuleCodeString`] trait, but
  /// it is highly recommended that embedders use the [`ascii_str!`] to generate the fastest version
  /// of strings for v8 to handle. If the strings are not static, you may also pass a [`String`]
  /// generated by the [`format!`] macro.
  pub fn execute_script(
    &mut self,
    name: impl IntoModuleName,
    source_code: impl IntoModuleCodeString,
  ) -> Result<v8::Global<v8::Value>, Box<JsError>> {
    let isolate = &mut self.inner.v8_isolate;
    self.inner.main_realm.execute_script(
      isolate,
      name.into_module_name(),
      source_code.into_module_code(),
    )
  }

  /// Call a function and return a future resolving with the return value of the
  /// function. If the function returns a promise, the future will resolve only once the
  /// event loop resolves the underlying promise. If the future rejects, the future will
  /// resolve with the underlying error.
  ///
  /// The event loop must be polled seperately for this future to resolve. If the event loop
  /// is not polled, the future will never make progress.
  pub fn call(
    &mut self,
    function: &v8::Global<v8::Function>,
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    self.call_with_args(function, &[])
  }

  /// Call a function and returns a future resolving with the return value of the
  /// function. If the function returns a promise, the future will resolve only once the
  /// event loop resolves the underlying promise. If the future rejects, the future will
  /// resolve with the underlying error.
  ///
  /// The event loop must be polled seperately for this future to resolve. If the event loop
  /// is not polled, the future will never make progress.
  pub fn scoped_call(
    scope: &mut v8::PinScope,
    function: &v8::Global<v8::Function>,
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    Self::scoped_call_with_args(scope, function, &[])
  }

  /// Call a function and returns a future resolving with the return value of the
  /// function. If the function returns a promise, the future will resolve only once the
  /// event loop resolves the underlying promise. If the future rejects, the future will
  /// resolve with the underlying error.
  ///
  /// The event loop must be polled seperately for this future to resolve. If the event loop
  /// is not polled, the future will never make progress.
  pub fn call_with_args(
    &mut self,
    function: &v8::Global<v8::Function>,
    args: &[v8::Global<v8::Value>],
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    scope!(scope, self);
    Self::scoped_call_with_args(scope, function, args)
  }

  /// Call a function and returns a future resolving with the return value of the
  /// function. If the function returns a promise, the future will resolve only once the
  /// event loop resolves the underlying promise. If the future rejects, the future will
  /// resolve with the underlying error.
  ///
  /// The event loop must be polled seperately for this future to resolve. If the event loop
  /// is not polled, the future will never make progress.
  pub fn scoped_call_with_args(
    scope: &mut v8::PinScope,
    function: &v8::Global<v8::Function>,
    args: &[v8::Global<v8::Value>],
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    v8::tc_scope!(let scope, scope);
    let cb = function.open(scope);
    let this = v8::undefined(scope).into();
    let promise = if args.is_empty() {
      cb.call(scope, this, &[])
    } else {
      let mut local_args: SmallVec<[v8::Local<v8::Value>; 8]> =
        SmallVec::with_capacity(args.len());
      for v in args {
        local_args.push(v8::Local::new(scope, v));
      }
      cb.call(scope, this, &local_args)
    };

    if promise.is_none() {
      if scope.is_execution_terminating() {
        let undefined = v8::undefined(scope).into();
        return RcPromiseFuture::new(exception_to_err_result(
          scope, undefined, false, true,
        ));
      }
      let exception = scope.exception().unwrap();
      return RcPromiseFuture::new(exception_to_err_result(
        scope, exception, false, true,
      ));
    }
    let promise = promise.unwrap();
    if !promise.is_promise() {
      return RcPromiseFuture::new(Ok(v8::Global::new(scope, promise)));
    }
    let promise = v8::Local::<v8::Promise>::try_from(promise).unwrap();
    Self::resolve_promise_inner(scope, promise)
  }

  /// Call a function. If it returns a promise, run the event loop until that
  /// promise is settled. If the promise rejects or there is an uncaught error
  /// in the event loop, return `Err(error)`. Or return `Ok(<await returned>)`.
  #[deprecated = "Use call"]
  pub async fn call_and_await(
    &mut self,
    function: &v8::Global<v8::Function>,
  ) -> Result<v8::Global<v8::Value>, CoreError> {
    let call = self.call(function);
    self
      .with_event_loop_promise(call, PollEventLoopOptions::default())
      .await
  }

  /// Call a function with args. If it returns a promise, run the event loop until that
  /// promise is settled. If the promise rejects or there is an uncaught error
  /// in the event loop, return `Err(error)`. Or return `Ok(<await returned>)`.
  #[deprecated = "Use call_with_args"]
  pub async fn call_with_args_and_await(
    &mut self,
    function: &v8::Global<v8::Function>,
    args: &[v8::Global<v8::Value>],
  ) -> Result<v8::Global<v8::Value>, CoreError> {
    let call = self.call_with_args(function, args);
    self
      .with_event_loop_promise(call, PollEventLoopOptions::default())
      .await
  }

  /// Returns the namespace object of a module.
  ///
  /// This is only available after module evaluation has completed.
  /// This function panics if module has not been instantiated.
  pub fn get_module_namespace(
    &mut self,
    module_id: ModuleId,
  ) -> Result<v8::Global<v8::Object>, CoreError> {
    let isolate = &mut self.inner.v8_isolate;
    self
      .inner
      .main_realm
      .get_module_namespace(isolate, module_id)
  }

  /// Registers a callback on the isolate when the memory limits are approached.
  /// Use this to prevent V8 from crashing the process when reaching the limit.
  ///
  /// Calls the closure with the current heap limit and the initial heap limit.
  /// The return value of the closure is set as the new limit.
  pub fn add_near_heap_limit_callback<C>(&mut self, cb: C)
  where
    C: FnMut(usize, usize) -> usize + 'static,
  {
    let boxed_cb = Box::new(RefCell::new(cb));
    let data = boxed_cb.as_ptr() as *mut c_void;

    let prev = self
      .allocations
      .near_heap_limit_callback_data
      .replace((boxed_cb, near_heap_limit_callback::<C>));
    if let Some((_, prev_cb)) = prev {
      self
        .v8_isolate()
        .remove_near_heap_limit_callback(prev_cb, 0);
    }

    self
      .v8_isolate()
      .add_near_heap_limit_callback(near_heap_limit_callback::<C>, data);
  }

  pub fn remove_near_heap_limit_callback(&mut self, heap_limit: usize) {
    if let Some((_, cb)) = self.allocations.near_heap_limit_callback_data.take()
    {
      self
        .v8_isolate()
        .remove_near_heap_limit_callback(cb, heap_limit);
    }
  }

  pub fn maybe_init_inspector(&mut self) {
    let inspector = &mut self.inner.state.inspector.borrow_mut();
    if inspector.is_some() {
      return;
    }

    let context = self.main_context();
    let isolate_ptr = unsafe { self.inner.v8_isolate.as_raw_isolate_ptr() };
    v8::scope_with_context!(
      scope,
      self.inner.v8_isolate.as_mut(),
      context.clone(),
    );
    let context = v8::Local::new(scope, context);

    self.inner.state.has_inspector.set(true);
    **inspector = Some(JsRuntimeInspector::new(
      isolate_ptr,
      scope,
      context,
      self.is_main_runtime,
      None,
    ));
  }

  /// Waits for the given value to resolve while polling the event loop.
  ///
  /// This future resolves when either the value is resolved or the event loop runs to
  /// completion.
  pub fn resolve(
    &mut self,
    promise: v8::Global<v8::Value>,
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    scope!(scope, self);
    Self::scoped_resolve(scope, promise)
  }

  /// Waits for the given value to resolve while polling the event loop.
  ///
  /// This future resolves when either the value is resolved or the event loop runs to
  /// completion.
  pub fn scoped_resolve(
    scope: &mut v8::PinScope,
    promise: v8::Global<v8::Value>,
  ) -> impl Future<Output = Result<v8::Global<v8::Value>, Box<JsError>>> + use<>
  {
    let promise = v8::Local::new(scope, promise);
    if !promise.is_promise() {
      return RcPromiseFuture::new(Ok(v8::Global::new(scope, promise)));
    }
    let promise = v8::Local::<v8::Promise>::try_from(promise).unwrap();
    Self::resolve_promise_inner(scope, promise)
  }

  /// Waits for the given value to resolve while polling the event loop.
  ///
  /// This future resolves when either the value is resolved or the event loop runs to
  /// completion.
  #[deprecated = "Use resolve"]
  pub async fn resolve_value(
    &mut self,
    global: v8::Global<v8::Value>,
  ) -> Result<v8::Global<v8::Value>, CoreError> {
    let resolve = self.resolve(global);
    self
      .with_event_loop_promise(resolve, PollEventLoopOptions::default())
      .await
  }

  /// Given a promise, returns a future that resolves when it does.
  fn resolve_promise_inner<'s, 'i>(
    scope: &mut v8::PinScope<'s, 'i>,
    promise: v8::Local<'s, v8::Promise>,
  ) -> RcPromiseFuture {
    let future = RcPromiseFuture::default();
    let f = future.clone();
    watch_promise(scope, promise, move |scope, _rv, res| {
      let res = match res {
        Ok(l) => Ok(v8::Global::new(scope, l)),
        Err(e) => exception_to_err_result(scope, e, true, true),
      };
      f.0.resolved.set(Some(res));
      if let Some(waker) = f.0.waker.take() {
        waker.wake();
      }
    });

    future
  }

  /// Runs event loop to completion
  ///
  /// This future resolves when:
  ///  - there are no more pending dynamic imports
  ///  - there are no more pending ops
  ///  - there are no more active inspector sessions (only if
  ///    `PollEventLoopOptions.wait_for_inspector` is set to true)
  pub async fn run_event_loop(
    &mut self,
    poll_options: PollEventLoopOptions,
  ) -> Result<(), CoreError> {
    poll_fn(|cx| self.poll_event_loop(cx, poll_options)).await
  }

  /// A utility function that run provided future concurrently with the event loop.
  ///
  /// If the event loop resolves while polling the future, it return an error with the text
  /// `Promise resolution is still pending but the event loop has already resolved`
  pub async fn with_event_loop_promise<'fut, T, E>(
    &mut self,
    mut fut: impl Future<Output = Result<T, E>> + Unpin + 'fut,
    poll_options: PollEventLoopOptions,
  ) -> Result<T, CoreError>
  where
    CoreError: From<E>,
  {
    // Manually implement tokio::select
    poll_fn(|cx| {
      if let Poll::Ready(t) = fut.poll_unpin(cx) {
        return Poll::Ready(t.map_err(|e| e.into()));
      }
      if let Poll::Ready(t) = self.poll_event_loop(cx, poll_options) {
        t?;
        if let Poll::Ready(t) = fut.poll_unpin(cx) {
          return Poll::Ready(t.map_err(|e| e.into()));
        }
        return Poll::Ready(Err(
          CoreErrorKind::PendingPromiseResolution.into_box(),
        ));
      }
      Poll::Pending
    })
    .await
  }

  /// A utility function that run provided future concurrently with the event loop.
  ///
  /// If the event loop resolves while polling the future, it will continue to be polled,
  /// regardless of whether it returned an error or success.
  ///
  /// Useful for interacting with local inspector session.
  pub async fn with_event_loop_future<'fut, T, E>(
    &mut self,
    mut fut: impl Future<Output = Result<T, E>> + Unpin + 'fut,
    poll_options: PollEventLoopOptions,
  ) -> Result<T, E> {
    // Manually implement tokio::select
    poll_fn(|cx| {
      if let Poll::Ready(t) = fut.poll_unpin(cx) {
        return Poll::Ready(t);
      }
      if let Poll::Ready(t) = self.poll_event_loop(cx, poll_options) {
        // TODO(mmastrac): We need to ignore this error for things like the repl to behave as
        // they did before, but this is definitely not correct. It's just something we're
        // relying on. :(
        _ = t;
      }
      Poll::Pending
    })
    .await
  }

  /// Runs a single tick of event loop
  ///
  /// If `PollEventLoopOptions.wait_for_inspector` is set to true, the event
  /// loop will return `Poll::Pending` if there are active inspector sessions.
  pub fn poll_event_loop(
    &mut self,
    cx: &mut Context,
    poll_options: PollEventLoopOptions,
  ) -> Poll<Result<(), CoreError>> {
    let has_inspector = self.inner.state.has_inspector.get();

    // SAFETY: We know this isolate is valid and non-null at this time
    let mut isolate =
      unsafe { v8::Isolate::from_raw_isolate_ptr(self.v8_isolate_ptr()) };

    let result = {
      v8::scope!(let isolate_scope, &mut isolate);
      let context =
        v8::Local::new(isolate_scope, self.inner.main_realm.context());
      let mut scope = v8::ContextScope::new(isolate_scope, context);
      self.poll_event_loop_inner(cx, &mut scope, poll_options)
    };

    // Tell V8's CPU profiler whether we're about to go idle. When the event
    // loop has no immediate work it returns `Poll::Pending` and the task parks
    // until an external event (timer, I/O) wakes it. Marking the isolate idle
    // makes the profiler attribute that wait to the `(idle)` node instead of
    // `(program)`, which otherwise makes an idle process look like it is using
    // 100% CPU in DevTools (https://github.com/denoland/deno/issues/21620).
    //
    // This must happen *after* the `v8::ContextScope` above is dropped: tearing
    // the scope down calls `Isolate::Exit`, which restores the VM state that was
    // saved on entry and would clobber the idle state if we set it any earlier.
    if has_inspector {
      isolate.set_idle(result.is_pending());
    }
    result
  }

  /// Phase-based event loop tick, loosely following libuv's architecture:
  ///
  /// 1. Timers          -- fire expired libuv C timers + JS user timers
  /// 2. Pending work     -- module progress, task spawner, async ops,
  ///    nextTick/macrotask drain, rejections
  /// 3. Idle / Prepare   -- libuv idle + prepare callbacks
  /// 4. I/O              -- drive TCP read/write/accept via UvLoopInner
  /// 5. Check            -- libuv check callbacks + immediates
  /// 6. Close            -- close callbacks (Rust + libuv)
  ///
  /// Microtask checkpoints run between phases.
  fn poll_event_loop_inner(
    &self,
    cx: &mut Context,
    scope: &mut v8::PinScope,
    poll_options: PollEventLoopOptions,
  ) -> Poll<Result<(), CoreError>> {
    let has_inspector = self.inner.state.has_inspector.get();
    self.inner.state.waker.register(cx.waker());

    // Pre-phase: Inspector + drain foreground tasks + microtask checkpoint
    if has_inspector {
      self.inspector().poll_sessions_from_event_loop(cx);
    }
    {
      // Drain and run foreground tasks queued by the custom V8 platform.
      // Uses the local Arc shared with the registry — no global map lookup.
      let tasks =
        std::mem::take(&mut *self.inner.state.foreground_tasks.lock().unwrap());
      for task in tasks {
        task.run();
      }

      v8::tc_scope!(let tc_scope, scope);
      let context_state = JsRealm::state_from_scope(tc_scope);
      if !context_state.has_tick_scheduled() {
        tc_scope.perform_microtask_checkpoint();
      }
      if let Some(exception) = tc_scope.exception() {
        return Poll::Ready(Err(
          exception_to_err_result::<()>(tc_scope, exception, false, true)
            .unwrap_err()
            .into(),
        ));
      }
    }

    let realm = &self.inner.main_realm;
    let modules = &realm.0.module_map;
    let context_state = &realm.0.context_state;

    let exception_state = &context_state.exception_state;

    // Tight I/O loop: when run_io does work, re-run I/O phases immediately
    // without returning to tokio. This avoids kqueue/kevent round-trip
    // latency between batches.
    let mut dispatched_ops = false;
    let mut did_work = false;
    let mut uv_did_io = false;
    // ===== Phase 1: Timers =====
    // 1a. Fire expired libuv C timers
    if let Some(uv_inner_ptr) = context_state.uv_loop_inner.get() {
      // Update cached loop time at the start of each tick, matching libuv.
      unsafe { (*uv_inner_ptr).update_time() };
      unsafe { (*uv_inner_ptr).run_timers() };
    }

    // ===== Phase 2: Pending work =====
    // Module progress polling (before ops, matching original ordering)
    modules.poll_progress(cx, scope)?;

    // 2a. V8 task spawner tasks
    dispatched_ops |= Self::dispatch_task_spawner(cx, scope, context_state);

    // 2b. Process expired JS timers first and immediately commit the
    // returned next-expiry state. Completed ops are resolved afterwards so
    // promise hooks that arm timers cannot be overwritten by an older timer
    // snapshot.
    let timer_ready = Self::dispatch_user_timers(cx, scope, context_state)?;
    did_work |= timer_ready;
    dispatched_ops |= Self::dispatch_event_loop_tick(cx, scope, context_state)?;
    // Microtask checkpoint after timer/op processing, but only when
    // no ticks are scheduled (matching original guard after timers).
    if !context_state.has_tick_scheduled() {
      scope.perform_microtask_checkpoint();
    }

    // 2c. Dispatch "rejectionhandled" events before tick processing.
    // This ensures rejectionhandled fires before unhandledrejection for
    // later promises, since processTicksAndRejections drains unhandled
    // rejections via processPromiseRejections.
    Self::dispatch_handled_rejections(scope, exception_state);

    // 2d. nextTick drain + macrotask drain.
    // Only drain if there's actual work (ops dispatched, tick scheduled,
    // or timers fired). This prevents macrotask callbacks from running
    // on empty iterations.
    let has_tick_scheduled = context_state.has_tick_scheduled();
    dispatched_ops |= has_tick_scheduled;
    if dispatched_ops || did_work || has_tick_scheduled {
      Self::drain_next_tick_and_macrotasks(scope, context_state)?;
    }

    // 2e. Handle promise rejections (after nextTick/macrotask, since
    // unhandledrejection handlers are run in macrotask callbacks).
    Self::dispatch_rejections(scope, context_state, exception_state)?;
    scope.perform_microtask_checkpoint();

    // ===== Phase 3: Idle / Prepare =====
    // In libuv: idle runs after pending callbacks, prepare runs right
    // before I/O polling. Both must precede I/O.
    let has_uv = context_state.uv_loop_inner.get().is_some();
    if let Some(uv_inner_ptr) = context_state.uv_loop_inner.get() {
      unsafe {
        (*uv_inner_ptr).run_idle();
        (*uv_inner_ptr).run_prepare();
      };
      // Idle/prepare callbacks may call into JS; flush microtasks.
      scope.perform_microtask_checkpoint();
    }

    // ===== Phase 4: I/O =====
    // Single run_io call per tick, matching libuv's uv_run (one
    // uv__io_poll per iteration, callbacks fire, then we return).
    // Spinning run_io in place until it returns `false` batches more
    // work per tick but under sustained inbound traffic never exits —
    // tokio keeps delivering readiness as we poll — and traps the
    // event loop processing hundreds of handles back-to-back, which
    // crushes tail latency (p99 30–200 ms vs ~1 ms with a single
    // call).
    if let Some(uv_inner_ptr) = context_state.uv_loop_inner.get() {
      unsafe {
        (*uv_inner_ptr).set_waker(cx.waker());
      }
      let did_io = unsafe { (*uv_inner_ptr).run_io() };
      if did_io {
        uv_did_io = true;
        // Flush microtasks from I/O callbacks, then drain ticks.
        // processTicksAndRejections runs op_run_microtasks internally,
        // so the trailing checkpoint is only needed when no ticks ran.
        scope.perform_microtask_checkpoint();
        Self::drain_next_tick_and_macrotasks(scope, context_state)?;
        if !context_state.has_tick_scheduled() {
          scope.perform_microtask_checkpoint();
        }
      }
    }

    // ===== Phase 5: Check =====
    // In libuv: check runs right after I/O polling.
    // Immediates fire here, matching Node.js's setImmediate semantics
    // (libuv check phase, after I/O).
    if let Some(uv_inner_ptr) = context_state.uv_loop_inner.get() {
      unsafe { (*uv_inner_ptr).run_check() };
    }
    // Drain immediates in the check phase, matching Node.js semantics:
    // - Refed immediates always fire (they keep the event loop alive).
    // - Unrefed immediates only fire if other work drove this iteration
    //   (did_work, dispatched_ops, or uv I/O). This matches libuv's
    //   behavior where unrefed handles participate in iterations driven
    //   by other work, but don't start new iterations on their own.
    {
      let has_immediates =
        context_state.immediate_info[IMM_IDX_HAS_OUTSTANDING] != 0
          || context_state.immediate_info[IMM_IDX_COUNT] > 0;
      let has_refed = context_state.immediate_info[IMM_IDX_REF_COUNT] > 0;
      if has_immediates
        && (has_refed || did_work || dispatched_ops || uv_did_io)
      {
        Self::do_js_run_immediate_callbacks(scope, context_state)?;
        // Drain ticks queued by immediate callbacks so they don't
        // require an extra full event loop iteration.
        if context_state.has_tick_scheduled() {
          Self::drain_next_tick_and_macrotasks(scope, context_state)?;
        }
      }
    }
    scope.perform_microtask_checkpoint();

    // Drain nextTick queue before close phase, matching Node.js/libuv
    // where process.nextTick fires between each event loop phase.
    // This ensures nextTicks from I/O callbacks (Phase 4) fire before
    // close callbacks (Phase 6).
    if context_state.has_tick_scheduled() {
      Self::drain_next_tick_and_macrotasks(scope, context_state)?;
    }

    // ===== Phase 6: Close =====
    exception_state.check_exception_condition(scope)?;
    {
      let mut phases = context_state.event_loop_phases.borrow_mut();
      phases.run_close_callbacks();
    }
    if let Some(uv_inner_ptr) = context_state.uv_loop_inner.get() {
      unsafe { (*uv_inner_ptr).run_close() };
    }
    // Run V8 close callbacks (JS handle.close() callbacks).
    // These are deferred to Phase 6 to match libuv's uv_close behavior
    // where close callbacks fire at the END of the event loop iteration,
    // after all nextTick and microtask queues have drained.
    {
      let v8_cbs = context_state
        .event_loop_phases
        .borrow_mut()
        .drain_v8_close_callbacks();
      for cb in v8_cbs {
        (cb.callback)(scope);
      }
    }
    // libuv close callbacks may call into JS; flush microtasks if present.
    if has_uv
      || !context_state
        .event_loop_phases
        .borrow()
        .v8_close_callbacks
        .is_empty()
    {
      scope.perform_microtask_checkpoint();
    }

    // Evaluate pending state
    let pending_state =
      EventLoopPendingState::new(scope, context_state, modules);

    if !pending_state.is_pending() {
      if has_inspector {
        let inspector = self.inspector();
        let sessions_state = inspector.sessions_state();

        if poll_options.wait_for_inspector && sessions_state.has_active {
          if sessions_state.has_blocking {
            return Poll::Pending;
          }

          if sessions_state.has_nonblocking_wait_for_disconnect {
            let context = self.main_context();
            inspector.context_destroyed(scope, context);
            self.wait_for_inspector_disconnect();
            return Poll::Pending;
          }
        }
      }

      return Poll::Ready(Ok(()));
    }

    // Re-wake logic for next iteration
    #[allow(
      clippy::suspicious_else_formatting,
      clippy::if_same_then_else,
      reason = "intentional structure for clarity of re-wake conditions"
    )]
    {
      if pending_state.has_pending_background_tasks
        || pending_state.has_tick_scheduled
        || pending_state.has_outstanding_immediates
        || context_state.immediate_info[IMM_IDX_REF_COUNT] > 0
        || pending_state.has_pending_promise_events
        || uv_did_io
      {
        self.inner.state.waker.wake();
      } else
      // If ops were dispatched we may have progress on pending modules that we should re-check
      if (pending_state.has_pending_module_evaluation
        || pending_state.has_pending_dyn_module_evaluation)
        && dispatched_ops
      {
        self.inner.state.waker.wake();
      }
    }

    if pending_state.has_pending_module_evaluation {
      if pending_state.has_pending_ops
        || pending_state.has_pending_dyn_imports
        || pending_state.has_pending_dyn_module_evaluation
        || pending_state.has_pending_background_tasks
        || pending_state.has_pending_external_ops
        || pending_state.has_tick_scheduled
        || pending_state.has_pending_timers
        || pending_state.has_uv_alive_handles
      {
        // pass, will be polled again
      } else {
        // Last-resort: try one more microtask checkpoint before reporting
        // a stalled TLA. Under Explicit microtask policy, V8's internal
        // async module evaluation state machine may require an additional
        // checkpoint to fully resolve the evaluation promise (e.g. when
        // TLA resumes trigger lazy module loads whose nested checkpoints
        // are no-ops due to V8's reentrancy guard).
        scope.perform_microtask_checkpoint();
        let modules = &realm.0.module_map();
        if !modules.has_pending_module_evaluation() {
          // The checkpoint resolved the evaluation -- keep going
          self.inner.state.tla_stall_retries.set(0);
          self.inner.state.waker.wake();
        } else if let Some(js_error) =
          find_and_report_stalled_level_await_in_any_realm(scope, &realm.0)
        {
          self.inner.state.tla_stall_retries.set(0);
          return Poll::Ready(Err(CoreErrorKind::Js(js_error).into_box()));
        } else {
          // V8 reports no stalled TLA but the evaluation promise is still
          // pending. This can happen with large async module graphs under
          // Explicit microtask policy. Give the event loop a few more
          // iterations to make progress, but bail if we are stuck.
          const MAX_TLA_STALL_RETRIES: u32 = 10;
          let retries = self.inner.state.tla_stall_retries.get() + 1;
          self.inner.state.tla_stall_retries.set(retries);
          if retries > MAX_TLA_STALL_RETRIES {
            self.inner.state.tla_stall_retries.set(0);
            return Poll::Ready(Err(
              CoreErrorKind::ModuleEvaluationDeadlock.into_box(),
            ));
          }
          #[allow(
            clippy::print_stderr,
            reason = "intentional debug diagnostic for TLA stall recovery"
          )]
          {
            eprintln!(
              "warning: module evaluation pending but no stalled top-level \
               await found, retrying event loop iteration ({retries}/{MAX_TLA_STALL_RETRIES})"
            );
          }
          self.inner.state.waker.wake();
        }
      }
    }

    if pending_state.has_pending_dyn_module_evaluation {
      if pending_state.has_pending_ops
        || pending_state.has_pending_dyn_imports
        || pending_state.has_pending_background_tasks
        || pending_state.has_pending_external_ops
        || pending_state.has_tick_scheduled
        || pending_state.has_pending_timers
        || pending_state.has_uv_alive_handles
      {
        // pass, will be polled again
      } else if realm.modules_idle() {
        if let Some(js_error) =
          find_and_report_stalled_level_await_in_any_realm(scope, &realm.0)
        {
          self.inner.state.tla_stall_retries.set(0);
          return Poll::Ready(Err(CoreErrorKind::Js(js_error).into_box()));
        } else {
          const MAX_TLA_STALL_RETRIES: u32 = 10;
          let retries = self.inner.state.tla_stall_retries.get() + 1;
          self.inner.state.tla_stall_retries.set(retries);
          if retries > MAX_TLA_STALL_RETRIES {
            self.inner.state.tla_stall_retries.set(0);
            return Poll::Ready(Err(
              CoreErrorKind::ModuleEvaluationDeadlock.into_box(),
            ));
          }
          #[allow(
            clippy::print_stderr,
            reason = "intentional debug diagnostic for TLA stall recovery"
          )]
          {
            eprintln!(
              "warning: dynamic module evaluation pending but no stalled \
               top-level await found, retrying event loop iteration \
               ({retries}/{MAX_TLA_STALL_RETRIES})"
            );
          }
          self.inner.state.waker.wake();
        }
      } else {
        realm.increment_modules_idle();
        self.inner.state.waker.wake();
      }
    }

    Poll::Pending
  }
}

fn find_and_report_stalled_level_await_in_any_realm(
  scope: &mut v8::PinScope,
  inner_realm: &JsRealmInner,
) -> Option<Box<JsError>> {
  let module_map = inner_realm.module_map();
  let messages = module_map.find_stalled_top_level_await(scope);

  if !messages.is_empty() {
    // We are gonna print only a single message to provide a nice formatting
    // with source line of offending promise shown. Once user fixed it, then
    // they will get another error message for the next promise (but this
    // situation is gonna be very rare, if ever happening).
    let msg = v8::Local::new(scope, &messages[0]);
    let js_error = JsError::from_v8_message(scope, msg);
    return Some(js_error);
  }

  None
}

fn create_context<'s, 'i>(
  scope: &mut v8::PinScope<'s, 'i, ()>,
  global_template_middlewares: &[GlobalTemplateMiddlewareFn],
  global_object_middlewares: &[GlobalObjectMiddlewareFn],
  has_snapshot: bool,
) -> v8::Local<'s, v8::Context> {
  let context = if has_snapshot {
    // Try to load the 1st index first, embedder may have used 0th for something else (like node:vm).
    v8::Context::from_snapshot(scope, 1, Default::default()).unwrap_or_else(
      || v8::Context::from_snapshot(scope, 0, Default::default()).unwrap(),
    )
  } else {
    // Set up the global object template and create context from it.
    let mut global_object_template = v8::ObjectTemplate::new(scope);
    for middleware in global_template_middlewares {
      global_object_template = middleware(scope, global_object_template);
    }

    global_object_template.set_internal_field_count(2);
    v8::Context::new(
      scope,
      v8::ContextOptions {
        global_template: Some(global_object_template),
        ..Default::default()
      },
    )
  };

  let scope = &mut v8::ContextScope::new(scope, context);

  let global = context.global(scope);
  for middleware in global_object_middlewares {
    middleware(scope, global);
  }
  context
}

impl JsRuntimeForSnapshot {
  /// Create a new runtime, panicking if the process fails.
  pub fn new(options: RuntimeOptions) -> JsRuntimeForSnapshot {
    match Self::try_new(options) {
      Ok(runtime) => runtime,
      Err(err) => {
        panic!("Failed to initialize JsRuntime for snapshotting: {:?}", err);
      }
    }
  }

  /// Try to create a new runtime, returning an error if the process fails.
  pub fn try_new(
    mut options: RuntimeOptions,
  ) -> Result<JsRuntimeForSnapshot, CoreError> {
    setup::init_v8(
      options.v8_platform.take(),
      true,
      options.unsafe_expose_natives_and_gc(),
    );

    let runtime = JsRuntime::new_inner(options, true)?;
    Ok(JsRuntimeForSnapshot(runtime))
  }

  /// Takes a snapshot and consumes the runtime.
  ///
  /// `Error` can usually be downcast to `JsError`.
  pub fn snapshot(mut self) -> Box<[u8]> {
    // Ensure there are no live inspectors to prevent crashes.
    self.inner.prepare_for_cleanup();
    let original_sources =
      std::mem::take(&mut self.0.allocations.original_sources);
    let lazy_source_specifiers =
      std::mem::take(&mut self.0.allocations.lazy_source_specifiers);
    // `lazy_loaded_*` sources are externalized for the snapshot (so consumed
    // sources bake in as clean external strings), but only the *consumed* ones
    // are actually referenced by snapshotted code. Non-consumed (residual)
    // sources are already shipped via the residual table, so persisting their
    // bytes here would duplicate them. Store empty bytes for those slots — the
    // external-reference index is preserved (nothing references it), avoiding
    // the duplication.
    let consumed: std::collections::HashSet<String> =
      self.consumed_lazy_specifiers().into_iter().collect();
    let lazy_source_start =
      original_sources.len() - lazy_source_specifiers.len();
    let external_strings = original_sources
      .iter()
      .enumerate()
      .map(|(i, s)| {
        if i >= lazy_source_start
          && !consumed
            .contains(lazy_source_specifiers[i - lazy_source_start].as_str())
        {
          return &[][..];
        }
        s.as_str().as_bytes()
      })
      .collect();
    let realm = JsRealm::clone(&self.inner.main_realm);

    // Set the context to be snapshot's default context
    {
      jsrealm::context_scope!(scope, realm, self.v8_isolate());
      let default_context = v8::Context::new(scope, Default::default());
      scope.set_default_context(default_context);

      let local_context = v8::Local::new(scope, realm.context());
      scope.add_context(local_context);
    }

    // Borrow the source maps during the snapshot to avoid copies
    let source_maps = self
      .inner
      .state
      .source_mapper
      .borrow_mut()
      .take_ext_source_maps();
    let mut ext_source_maps = HashMap::with_capacity(source_maps.len());
    for (k, v) in &source_maps {
      ext_source_maps.insert(k.as_static_str().unwrap(), v.as_ref());
    }

    // Serialize the module map and store its data in the snapshot.
    // TODO(mmastrac): This should deconstruct the realm into sidecar data rather than
    // extracting it from the realm and then tearing the realm down. IE, this should
    // probably be a method on `JsRealm` with a self-consuming parameter signature:
    // `fn into_sidecar_data(self) -> ...`.
    let sidecar_data = {
      let mut data_store = SnapshotStoreDataStore::default();
      let module_map_data = {
        let module_map = realm.0.module_map();
        module_map.serialize_for_snapshotting(&mut data_store)
      };
      let function_templates_data = {
        let function_templates = realm.0.function_templates();
        let f = std::mem::take(&mut *function_templates.borrow_mut());

        f.serialize_for_snapshotting(&mut data_store)
      };
      let maybe_js_handled_promise_rejection_cb = {
        let context_state = &realm.0.context_state;
        let exception_state = &context_state.exception_state;
        exception_state
          .js_handled_promise_rejection_cb
          .borrow()
          .clone()
      }
      .map(|cb| data_store.register(cb));

      let ext_import_meta_proto = realm
        .0
        .context_state
        .ext_import_meta_proto
        .borrow()
        .clone()
        .map(|p| data_store.register(p));

      let snapshotted_data = SnapshottedData {
        module_map_data,
        function_templates_data,
        op_count: self.inner.op_count,
        addl_refs_count: self.inner.addl_refs_count,
        source_count: self.inner.source_count,
        extensions: self.inner.extensions.clone(),
        js_handled_promise_rejection_cb: maybe_js_handled_promise_rejection_cb,
        ext_import_meta_proto,
        ext_source_maps,
        external_strings,
      };

      jsrealm::context_scope!(scope, realm, self.v8_isolate());
      snapshot::store_snapshotted_data_for_snapshot(
        scope,
        realm.context().clone(),
        snapshotted_data,
        data_store,
      )
    };
    drop(realm);

    let v8_data = self
      .0
      .inner
      .prepare_for_snapshot()
      .create_blob(v8::FunctionCodeHandling::Keep)
      .unwrap();

    snapshot::serialize(v8_data, sidecar_data)
  }
}

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub(crate) struct EventLoopPendingState {
  has_pending_ops: bool,
  has_pending_refed_ops: bool,
  has_pending_dyn_imports: bool,
  has_pending_dyn_module_evaluation: bool,
  has_pending_module_evaluation: bool,
  has_pending_background_tasks: bool,
  has_tick_scheduled: bool,
  has_pending_promise_events: bool,
  has_pending_external_ops: bool,
  has_outstanding_immediates: bool,
  has_pending_timers: bool,
  has_uv_alive_handles: bool,
}

impl EventLoopPendingState {
  /// Collect event loop state from all the sub-states.
  pub fn new(
    scope: &mut v8::PinScope<()>,
    state: &ContextState,
    modules: &ModuleMap,
  ) -> Self {
    let num_unrefed_ops = state.unrefed_ops.borrow().len();
    let num_pending_ops = state.pending_ops.len();
    let has_pending_tasks = state.task_spawner_factory.has_pending_tasks();
    // User timers: JS manages these; the timer handle is refed when
    // there are refed timers (timer_info[0] > 0).
    let has_pending_refed_user_timers = state.user_timer.is_refed();
    let has_pending_dyn_imports = modules.has_pending_dynamic_imports();
    let has_pending_dyn_module_evaluation =
      modules.has_pending_dyn_module_evaluation();
    let has_pending_module_evaluation = modules.has_pending_module_evaluation();
    let has_pending_promise_events = !state
      .exception_state
      .pending_promise_rejections
      .borrow()
      .is_empty()
      || !state
        .exception_state
        .pending_handled_promise_rejections
        .borrow()
        .is_empty();
    let has_pending_refed_ops = has_pending_tasks
      || has_pending_refed_user_timers
      || num_pending_ops > num_unrefed_ops;
    let has_outstanding_immediates =
      state.immediate_info[IMM_IDX_HAS_OUTSTANDING] != 0;
    let has_pending_timers = !state.active_timers.borrow().is_empty();
    let has_uv_alive_handles =
      if let Some(uv_inner_ptr) = state.uv_loop_inner.get() {
        unsafe { (*uv_inner_ptr).has_alive_handles() }
      } else {
        false
      };
    EventLoopPendingState {
      has_pending_ops: has_pending_refed_ops || (num_pending_ops > 0),
      has_pending_refed_ops,
      has_pending_dyn_imports,
      has_pending_dyn_module_evaluation,
      has_pending_module_evaluation,
      has_pending_background_tasks: scope.has_pending_background_tasks(),
      has_tick_scheduled: state.has_tick_scheduled(),
      has_pending_promise_events,
      has_pending_external_ops: state.external_ops_tracker.has_pending_ops(),
      has_outstanding_immediates,
      has_pending_timers,
      has_uv_alive_handles,
    }
  }

  /// Collect event loop state from all the states stored in the scope.
  pub fn new_from_scope(scope: &mut v8::PinScope) -> Self {
    let module_map = JsRealm::module_map_from(scope);
    let context_state = JsRealm::state_from_scope(scope);
    Self::new(scope, &context_state, &module_map)
  }

  pub fn is_pending(&self) -> bool {
    self.has_pending_refed_ops
      || self.has_pending_dyn_imports
      || self.has_pending_dyn_module_evaluation
      || self.has_pending_module_evaluation
      || self.has_pending_background_tasks
      || self.has_tick_scheduled
      || self.has_pending_promise_events
      || self.has_pending_external_ops
      || self.has_uv_alive_handles
  }
}

extern "C" fn near_heap_limit_callback<F>(
  data: *mut c_void,
  current_heap_limit: usize,
  initial_heap_limit: usize,
) -> usize
where
  F: FnMut(usize, usize) -> usize,
{
  // SAFETY: The data is a pointer to the Rust callback function. It is stored
  // in `JsRuntime::allocations` and thus is guaranteed to outlive the isolate.
  let callback = unsafe { &mut *(data as *mut F) };
  callback(current_heap_limit, initial_heap_limit)
}

impl JsRuntimeState {
  pub(crate) fn inspector(&self) -> Rc<JsRuntimeInspector> {
    self.inspector.borrow().as_ref().unwrap().clone()
  }

  /// Called by `bindings::host_import_module_dynamically_callback`
  /// after initiating new dynamic import load.
  pub fn notify_new_dynamic_import(&self) {
    // Notify event loop to poll again soon.
    self.waker.wake();
  }

  /// Performs an action with the inspector, if we have one
  pub(crate) fn with_inspector<T>(
    &self,
    mut f: impl FnMut(&JsRuntimeInspector) -> T,
  ) -> Option<T> {
    // Fast path
    if !self.has_inspector.get() {
      return None;
    }
    self
      .inspector
      .borrow()
      .as_ref()
      .map(|inspector| f(inspector))
  }
}

// Related to module loading
impl JsRuntime {
  #[cfg(test)]
  pub(crate) fn instantiate_module(
    &mut self,
    id: ModuleId,
  ) -> Result<(), v8::Global<v8::Value>> {
    let isolate = &mut *self.inner.v8_isolate;
    let realm = JsRealm::clone(&self.inner.main_realm);
    jsrealm::context_scope!(scope, realm, isolate);
    realm.instantiate_module(scope, id)
  }

  /// Evaluates an already instantiated ES module.
  ///
  /// Returns a future that resolves when module promise resolves.
  /// Implementors must manually call [`JsRuntime::run_event_loop`] to drive
  /// module evaluation future.
  ///
  /// Modules with top-level await are treated like promises, so a `throw` in the top-level
  /// block of a module is treated as an unhandled rejection. These rejections are provided to
  /// the unhandled promise rejection handler, which has the opportunity to pass them off to
  /// error-handling code. If those rejections are not handled (indicated by a `false` return
  /// from that unhandled promise rejection handler), then the runtime will terminate.
  ///
  /// The future provided by `mod_evaluate` will only return errors in the case where
  /// the runtime is shutdown and no longer available to provide unhandled rejection
  /// information.
  ///
  /// This function panics if module has not been instantiated.
  pub fn mod_evaluate(
    &mut self,
    id: ModuleId,
  ) -> impl Future<Output = Result<(), CoreError>> + use<> {
    let isolate = &mut *self.inner.v8_isolate;
    let realm = &self.inner.main_realm;
    jsrealm::context_scope!(scope, realm, isolate);
    self.inner.main_realm.0.module_map.mod_evaluate(scope, id)
  }

  /// Asynchronously load specified module and all of its dependencies.
  ///
  /// The module will be marked as "main", and because of that
  /// "import.meta.main" will return true when checked inside that module.
  ///
  /// The source may be any type that implements the internal [`IntoModuleCodeString`] trait, but
  /// it is highly recommended that embedders use the [`ascii_str!`] to generate the fastest version
  /// of strings for v8 to handle. If the strings are not static, you may also pass a [`String`]
  /// generated by the [`format!`] macro.
  ///
  /// User must call [`JsRuntime::mod_evaluate`] with returned `ModuleId`
  /// manually after load is finished.
  pub async fn load_main_es_module_from_code(
    &mut self,
    specifier: &ModuleSpecifier,
    code: impl IntoModuleCodeString,
  ) -> Result<ModuleId, CoreError> {
    self
      .drive_es_module_load(true, specifier, Some(code.into_module_code()))
      .await
  }

  /// Asynchronously load specified module and all of its dependencies, retrieving
  /// the module from the supplied [`ModuleLoader`].
  ///
  /// The module will be marked as "main", and because of that
  /// "import.meta.main" will return true when checked inside that module.
  ///
  /// User must call [`JsRuntime::mod_evaluate`] with returned `ModuleId`
  /// manually after load is finished.
  pub async fn load_main_es_module(
    &mut self,
    specifier: &ModuleSpecifier,
  ) -> Result<ModuleId, CoreError> {
    self.drive_es_module_load(true, specifier, None).await
  }

  /// Asynchronously load specified ES module and all of its dependencies from the
  /// provided source.
  ///
  /// This method is meant to be used when loading some utility code that
  /// might be later imported by the main module (ie. an entry point module).
  ///
  /// The source may be any type that implements the internal [`IntoModuleCodeString`] trait, but
  /// it is highly recommended that embedders use the [`ascii_str!`] to generate the fastest version
  /// of strings for v8 to handle. If the strings are not static, you may also pass a [`String`]
  /// generated by the [`format!`] macro.
  ///
  /// User must call [`JsRuntime::mod_evaluate`] with returned `ModuleId`
  /// manually after load is finished.
  pub async fn load_side_es_module_from_code(
    &mut self,
    specifier: &ModuleSpecifier,
    code: impl IntoModuleCodeString,
  ) -> Result<ModuleId, CoreError> {
    self
      .drive_es_module_load(false, specifier, Some(code.into_module_code()))
      .await
  }

  /// Asynchronously load specified ES module and all of its dependencies, retrieving
  /// the module from the supplied [`ModuleLoader`].
  ///
  /// This method is meant to be used when loading some utility code that
  /// might be later imported by the main module (ie. an entry point module).
  ///
  /// User must call [`JsRuntime::mod_evaluate`] with returned `ModuleId`
  /// manually after load is finished.
  pub async fn load_side_es_module(
    &mut self,
    specifier: &ModuleSpecifier,
  ) -> Result<ModuleId, CoreError> {
    self.drive_es_module_load(false, specifier, None).await
  }

  /// Drive a recursive ES module load to completion while concurrently
  /// pumping the event loop. The event loop pumping is required so that
  /// JavaScript-side `module.registerHooks()` load hooks (which run as an
  /// async polling task) can respond to load requests from the recursive
  /// load. Without it, static module loads that go through hook bridges
  /// would deadlock.
  async fn drive_es_module_load(
    &mut self,
    is_main: bool,
    specifier: &ModuleSpecifier,
    code: Option<ModuleCodeString>,
  ) -> Result<ModuleId, CoreError> {
    let realm = JsRealm::clone(&self.inner.main_realm);
    let module_map_rc = realm.0.module_map();

    // Only pump the V8 event loop alongside the load when the loader resolves
    // modules through asynchronous JavaScript (e.g. Node
    // `module.registerHooks()` load hooks). For ordinary loads pumping is
    // unnecessary and would run unrelated event-loop work mid-load, so the
    // load is driven on its own instead.
    let pump_event_loop =
      module_map_rc.loader.borrow().pump_event_loop_during_load();

    if let Some(code) = code {
      jsrealm::context_scope!(scope, &realm, self.v8_isolate());
      module_map_rc
        .new_es_module(
          scope,
          is_main,
          specifier.to_string().into(),
          code,
          false,
          None,
        )
        .map_err(|e| e.into_error(scope, false, false))?;
    }

    let mut load = if is_main {
      RecursiveModuleLoad::main(specifier.to_string(), module_map_rc.clone())
        .await?
    } else {
      RecursiveModuleLoad::side(
        specifier.to_string(),
        module_map_rc.clone(),
        SideModuleKind::Async,
        None,
      )
      .await?
    };

    loop {
      // Drive the recursive load, optionally pumping the V8 event loop
      // concurrently. Pumping is what lets JavaScript-side module hooks
      // (`module.registerHooks()`) respond to load requests issued by the
      // recursive load via the async hook bridge; for ordinary loads it is
      // skipped so unrelated event-loop work doesn't run mid-load.
      let next_step = poll_fn(|cx| {
        if let Poll::Ready(t) = load.poll_next_unpin(cx) {
          return Poll::Ready(Ok::<_, CoreError>(t));
        }
        if !pump_event_loop {
          return Poll::Pending;
        }
        match self.poll_event_loop(cx, PollEventLoopOptions::default()) {
          Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
          Poll::Ready(Ok(())) | Poll::Pending => {}
        }
        // After polling the event loop, the recursive load may have new
        // results ready (e.g. a hook callback responded). Re-poll.
        match load.poll_next_unpin(cx) {
          Poll::Ready(t) => Poll::Ready(Ok(t)),
          Poll::Pending => Poll::Pending,
        }
      })
      .await?;

      let Some(load_result) = next_step else { break };
      let (request, source) = load_result?;

      jsrealm::context_scope!(scope, &realm, self.v8_isolate());
      load
        .register_and_recurse(scope, &request, source)
        .map_err(|e| e.into_error(scope, false, false))?;
    }

    let root_id = load.root_module_id().expect("Root module should be loaded");

    jsrealm::context_scope!(scope, &realm, self.v8_isolate());
    realm.instantiate_module(scope, root_id).map_err(|e| {
      let exception = v8::Local::new(scope, e);
      CoreErrorKind::Js(crate::error::exception_to_err(
        scope, exception, false, false,
      ))
      .into_box()
    })?;

    Ok(root_id)
  }

  /// Load and evaluate an ES module provided the specifier and source code.
  ///
  /// The module should not have Top-Level Await (that is, it should be
  /// possible to evaluate it synchronously).
  ///
  /// It is caller's responsibility to ensure that not duplicate specifiers are
  /// passed to this method.
  pub fn lazy_load_es_module_with_code(
    &mut self,
    specifier: impl IntoModuleName,
    code: impl IntoModuleCodeString,
  ) -> Result<v8::Global<v8::Value>, CoreError> {
    let isolate = &mut self.inner.v8_isolate;
    self.inner.main_realm.lazy_load_es_module_with_code(
      isolate,
      specifier.into_module_name(),
      code.into_module_code(),
    )
  }

  fn do_js_run_immediate_callbacks<'s, 'i>(
    scope: &mut v8::PinScope<'s, 'i>,
    context_state: &ContextState,
  ) -> Result<(), Box<JsError>> {
    v8::tc_scope!(let tc_scope, scope);

    let undefined = v8::undefined(tc_scope).into();
    let run_immediate_callbacks_cb =
      context_state.run_immediate_callbacks_cb.borrow();
    let run_immediate_callbacks_cb =
      run_immediate_callbacks_cb.as_ref().unwrap().open(tc_scope);

    run_immediate_callbacks_cb.call(tc_scope, undefined, &[]);

    if let Some(exception) = tc_scope.exception() {
      let e: Result<(), Box<JsError>> =
        exception_to_err_result(tc_scope, exception, false, true);
      return e;
    }
    Ok(())
  }

  /// Schedule the next timer wake-up from the value returned by JS
  /// `__processTimers(now)`.
  ///
  /// The JS side returns:
  ///   - positive: next expiry time (has refed timers)
  ///   - negative: next expiry time negated (only unrefed timers)
  ///   - 0.0: no timers remain
  fn schedule_timer_expiry(context_state: &ContextState, expiry_ms: f64) {
    if expiry_ms != 0.0 {
      let next_expiry = expiry_ms.abs();
      let current_now = context_state.user_timer.now();
      let delay_ms = if next_expiry > current_now {
        (next_expiry - current_now) as u64
      } else {
        0
      };
      context_state
        .user_timer
        .schedule(std::time::Duration::from_millis(if delay_ms > 0 {
          delay_ms
        } else {
          1
        }));

      if expiry_ms > 0.0 {
        context_state.user_timer.ref_timer();
      } else {
        context_state.user_timer.unref_timer();
      }
    } else {
      context_state.user_timer.clear();
      context_state.user_timer.unref_timer();
    }
  }

  /// Phase 2b: Poll the user timer and call JS `__processTimers(now)`.
  /// The returned value is committed before async op resolution runs.
  fn dispatch_user_timers<'s, 'i>(
    cx: &mut Context,
    scope: &mut v8::PinScope<'s, 'i>,
    context_state: &ContextState,
  ) -> Result<bool, Box<JsError>> {
    if context_state.user_timer.poll_ready(cx).is_pending() {
      return Ok(false);
    }

    // `now` is passed to JS raw, with no clamp. The old single-function
    // `__eventLoopTick(timerNow, ...)` protocol clamped `now <= 0.0` to
    // `f64::EPSILON` so the timer argument could never collide with the
    // negative "skip timers" sentinel it shared with op resolution. This
    // protocol has no such sentinel: `__processTimers(now)` is a dedicated
    // call made only when the timer is ready, and `processTimers` only
    // compares `list.expiry > now` (every real timer's expiry exceeds a 0.0
    // startup `now`), so a raw 0.0 cannot mis-fire a timer.
    let now = context_state.user_timer.now();
    v8::tc_scope!(let tc_scope, scope);

    let process_timers_cb = context_state.js_process_timers_cb.borrow();
    let process_timers_fn = process_timers_cb.as_ref().unwrap().open(tc_scope);
    let now_val = v8::Number::new(tc_scope, now);
    let undefined: v8::Local<v8::Value> = v8::undefined(tc_scope).into();

    let result = process_timers_fn.call(tc_scope, undefined, &[now_val.into()]);

    if let Some(exception) = tc_scope.exception() {
      return exception_to_err_result(tc_scope, exception, false, true);
    }
    if tc_scope.has_terminated() || tc_scope.is_execution_terminating() {
      return Ok(false);
    }

    if let Some(result) = result {
      let expiry_ms = result.number_value(tc_scope).unwrap_or(0.0);
      Self::schedule_timer_expiry(context_state, expiry_ms);
    }

    Ok(true)
  }

  /// Phase 2a: Poll and dispatch V8 task spawner tasks.
  fn dispatch_task_spawner(
    cx: &mut Context,
    scope: &mut v8::PinScope,
    context_state: &ContextState,
  ) -> bool {
    let mut dispatched = false;
    let mut retries = 3;
    while let Poll::Ready(tasks) =
      context_state.task_spawner_factory.poll_inner(cx)
    {
      dispatched = true;
      for task in tasks {
        task(scope);
      }
      if !context_state.has_tick_scheduled() {
        scope.perform_microtask_checkpoint();
      }

      retries -= 1;
      if retries == 0 {
        cx.waker().wake_by_ref();
        break;
      }
    }
    dispatched
  }

  /// Phase 2c: Resolve completed async ops in a single Rust-to-JS call via
  /// `__eventLoopTick(promiseId, isOk, res, ...)`.
  ///
  /// If no ops are ready, returns Ok(false) and the
  /// caller should use drain_next_tick_and_macrotasks for any pending ticks.
  fn dispatch_event_loop_tick<'s, 'i>(
    cx: &mut Context,
    scope: &mut v8::PinScope<'s, 'i>,
    context_state: &ContextState,
  ) -> Result<bool, Box<JsError>> {
    const MAX_VEC_SIZE_FOR_OPS: usize = 1024;

    let mut args: SmallVec<[v8::Local<v8::Value>; 32]> =
      SmallVec::with_capacity(32);

    // Completed async ops as (promiseId, isOk, res) triplets.
    loop {
      // Ensure there is room for the next (promiseId, isOk, res) triplet
      if args.len() + 3 > MAX_VEC_SIZE_FOR_OPS {
        cx.waker().wake_by_ref();
        break;
      }

      let Poll::Ready((promise_id, op_id, res)) =
        context_state.pending_ops.poll_ready(cx)
      else {
        break;
      };

      let res = res.unwrap(scope);

      {
        let op_ctx = &context_state.op_ctxs[op_id as usize];
        if op_ctx.metrics_enabled() {
          if res.is_ok() {
            dispatch_metrics_async(op_ctx, OpMetricsEvent::CompletedAsync);
          } else {
            dispatch_metrics_async(op_ctx, OpMetricsEvent::ErrorAsync);
          }
        }
      }

      context_state.unrefed_ops.borrow_mut().remove(&promise_id);
      context_state
        .activity_traces
        .complete(RuntimeActivityType::AsyncOp, promise_id as _);
      args.push(v8::Integer::new(scope, promise_id).into());
      args.push(v8::Boolean::new(scope, res.is_ok()).into());
      args.push(res.unwrap_or_else(std::convert::identity));
    }

    // Skip the call if no ops completed.
    let has_ops = !args.is_empty();
    if !has_ops {
      return Ok(false);
    }

    let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();

    v8::tc_scope!(let tc_scope, scope);

    let tick_cb = context_state.js_event_loop_tick_cb.borrow();
    let tick_fn = tick_cb.as_ref().unwrap().open(tc_scope);
    tick_fn.call(tc_scope, undefined, args.as_slice());

    if let Some(exception) = tc_scope.exception() {
      return exception_to_err_result(tc_scope, exception, false, true);
    }
    if tc_scope.has_terminated() || tc_scope.is_execution_terminating() {
      return Ok(false);
    }

    Ok(has_ops)
  }

  /// Dispatch "rejectionhandled" events for promises that were previously
  /// reported as unhandled but have since had handlers attached.
  /// This must run before unhandled rejection processing so that
  /// rejectionhandled fires before unhandledrejection for later promises.
  fn dispatch_handled_rejections<'s, 'i>(
    scope: &mut v8::PinScope<'s, 'i>,
    exception_state: &ExceptionState,
  ) {
    let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();
    while let Some((promise, result)) = exception_state
      .pending_handled_promise_rejections
      .borrow_mut()
      .pop_front()
    {
      if let Some(handler) = exception_state
        .js_handled_promise_rejection_cb
        .borrow()
        .as_ref()
      {
        let function = handler.open(scope);
        let args = [
          v8::Local::new(scope, promise).into(),
          v8::Local::new(scope, result),
        ];
        function.call(scope, undefined, &args);
      }
    }
  }

  /// Phase 2c: Handle promise rejections.
  fn dispatch_rejections<'s, 'i>(
    scope: &mut v8::PinScope<'s, 'i>,
    context_state: &ContextState,
    exception_state: &ExceptionState,
  ) -> Result<(), Box<JsError>> {
    // First handle "handled" rejections
    Self::dispatch_handled_rejections(scope, exception_state);

    // Then handle unhandled rejections
    if exception_state
      .pending_promise_rejections
      .borrow()
      .is_empty()
    {
      return Ok(());
    }

    let mut pending_rejections =
      exception_state.pending_promise_rejections.borrow_mut();
    let mut rejections = VecDeque::default();
    std::mem::swap(&mut *pending_rejections, &mut rejections);
    drop(pending_rejections);

    let mut args: SmallVec<[v8::Local<v8::Value>; 16]> =
      SmallVec::with_capacity(rejections.len() * 3);
    for rejection in rejections.into_iter() {
      args.push(v8::Local::new(scope, rejection.0).into());
      args.push(v8::Local::new(scope, rejection.1));
      args.push(v8::Local::new(scope, rejection.2));
    }

    v8::tc_scope!(let tc_scope, scope);

    let handle_rejections_cb = context_state.js_handle_rejections_cb.borrow();
    let handle_rejections_fn =
      handle_rejections_cb.as_ref().unwrap().open(tc_scope);
    let undefined: v8::Local<v8::Value> = v8::undefined(tc_scope).into();
    handle_rejections_fn.call(tc_scope, undefined, args.as_slice());

    if let Some(exception) = tc_scope.exception() {
      return exception_to_err_result(tc_scope, exception, false, true);
    }

    Ok(())
  }

  /// Drain nextTick queue and macrotask queue (no op resolution).
  /// Used when ticks are pending but no async ops completed.
  ///
  /// This mirrors the JS `drainTicks()` (see `01_core.js`) exactly, but keeps
  /// the common path — no `process.nextTick` scheduled and no promise rejection
  /// to warn about, which is every pure-Deno workload — entirely on the Rust
  /// side. In that case `drainTicks` just runs `op_run_microtasks()` (a
  /// `perform_microtask_checkpoint`) and returns; doing it here avoids a
  /// Rust->JS call plus the JS->Rust op call it would otherwise make. Only when
  /// a tick or rejection is actually pending do we cross into JS to run
  /// `processTicksAndRejections`. The flag checks and checkpoint ordering are
  /// byte-for-byte identical to `drainTicks`, so the nextTick-before-`.then`
  /// and rejectionhandled-before-unhandledrejection invariants are preserved.
  fn drain_next_tick_and_macrotasks<'s, 'i>(
    scope: &mut v8::PinScope<'s, 'i>,
    context_state: &ContextState,
  ) -> Result<(), Box<JsError>> {
    if !context_state.has_tick_scheduled()
      && !context_state.has_rejection_to_warn()
    {
      scope.perform_microtask_checkpoint();
      if !context_state.has_tick_scheduled()
        && !context_state.has_rejection_to_warn()
      {
        return Ok(());
      }
    }

    // Slow path: a nextTick or rejection is pending. Cross into JS to run
    // `drainTicks`, which goes straight to `processTicksAndRejections` given
    // the flags above.
    let undefined: v8::Local<v8::Value> = v8::undefined(scope).into();

    v8::tc_scope!(let tc_scope, scope);

    let drain_cb = context_state.js_drain_next_tick_and_macrotasks_cb.borrow();
    let drain_fn = drain_cb.as_ref().unwrap().open(tc_scope);
    drain_fn.call(tc_scope, undefined, &[]);

    if let Some(exception) = tc_scope.exception() {
      return exception_to_err_result(tc_scope, exception, false, true);
    }

    Ok(())
  }
}

fn mark_as_loaded_from_fs_during_snapshot(
  files_loaded: &mut Vec<&'static str>,
  source: &ExtensionFileSourceCode,
) {
  #[allow(
    deprecated,
    reason = "needed for compatibility with snapshot loading"
  )]
  if let ExtensionFileSourceCode::LoadedFromFsDuringSnapshot(path) = source {
    files_loaded.push(path);
  }
}