jdk

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/*
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 * Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#include "precompiled.hpp"
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#include "gc/shared/collectedHeap.hpp"
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#include "gc/shared/oopStorage.inline.hpp"
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#include "gc/shared/oopStorageSet.hpp"
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#include "logging/log.hpp"
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#include "memory/iterator.hpp"
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#include "memory/universe.hpp"
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#include "oops/access.inline.hpp"
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#include "oops/oop.inline.hpp"
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#include "runtime/handles.inline.hpp"
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#include "runtime/javaThread.inline.hpp"
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#include "runtime/jniHandles.inline.hpp"
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#include "runtime/mutexLocker.hpp"
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#include "utilities/align.hpp"
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#include "utilities/debug.hpp"
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OopStorage* JNIHandles::global_handles() {
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  return _global_handles;
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}
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OopStorage* JNIHandles::weak_global_handles() {
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  return _weak_global_handles;
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}
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// Serviceability agent support.
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OopStorage* JNIHandles::_global_handles = nullptr;
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OopStorage* JNIHandles::_weak_global_handles = nullptr;
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void jni_handles_init() {
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  JNIHandles::_global_handles = OopStorageSet::create_strong("JNI Global", mtInternal);
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  JNIHandles::_weak_global_handles = OopStorageSet::create_weak("JNI Weak", mtInternal);
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}
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jobject JNIHandles::make_local(oop obj) {
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  return make_local(JavaThread::current(), obj);
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}
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// Used by NewLocalRef which requires null on out-of-memory
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jobject JNIHandles::make_local(JavaThread* thread, oop obj, AllocFailType alloc_failmode) {
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  if (obj == nullptr) {
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    return nullptr;                // ignore null handles
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  } else {
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    assert(oopDesc::is_oop(obj), "not an oop");
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    assert(!current_thread_in_native(), "must not be in native");
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    STATIC_ASSERT(TypeTag::local == 0);
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    return thread->active_handles()->allocate_handle(thread, obj, alloc_failmode);
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  }
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}
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static void report_handle_allocation_failure(AllocFailType alloc_failmode,
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                                             const char* handle_kind) {
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  if (alloc_failmode == AllocFailStrategy::EXIT_OOM) {
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    // Fake size value, since we don't know the min allocation size here.
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    vm_exit_out_of_memory(sizeof(oop), OOM_MALLOC_ERROR,
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                          "Cannot create %s JNI handle", handle_kind);
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  } else {
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    assert(alloc_failmode == AllocFailStrategy::RETURN_NULL, "invariant");
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  }
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}
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jobject JNIHandles::make_global(Handle obj, AllocFailType alloc_failmode) {
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  assert(!Universe::heap()->is_stw_gc_active(), "can't extend the root set during GC pause");
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  assert(!current_thread_in_native(), "must not be in native");
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  jobject res = nullptr;
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  if (!obj.is_null()) {
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    // ignore null handles
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    assert(oopDesc::is_oop(obj()), "not an oop");
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    oop* ptr = global_handles()->allocate();
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    // Return null on allocation failure.
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    if (ptr != nullptr) {
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      assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
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      NativeAccess<>::oop_store(ptr, obj());
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      char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::global;
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      res = reinterpret_cast<jobject>(tptr);
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    } else {
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      report_handle_allocation_failure(alloc_failmode, "global");
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    }
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  }
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  return res;
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}
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jweak JNIHandles::make_weak_global(Handle obj, AllocFailType alloc_failmode) {
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  assert(!Universe::heap()->is_stw_gc_active(), "can't extend the root set during GC pause");
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  assert(!current_thread_in_native(), "must not be in native");
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  jweak res = nullptr;
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  if (!obj.is_null()) {
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    // ignore null handles
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    assert(oopDesc::is_oop(obj()), "not an oop");
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    oop* ptr = weak_global_handles()->allocate();
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    // Return nullptr on allocation failure.
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    if (ptr != nullptr) {
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      assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
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      NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(ptr, obj());
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      char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::weak_global;
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      res = reinterpret_cast<jweak>(tptr);
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    } else {
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      report_handle_allocation_failure(alloc_failmode, "weak global");
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    }
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  }
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  return res;
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}
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// Resolve some erroneous cases to null, rather than treating them as
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// possibly unchecked errors.  In particular, deleted handles are
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// treated as null (though a deleted and later reallocated handle
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// isn't detected).
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oop JNIHandles::resolve_external_guard(jobject handle) {
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  oop result = nullptr;
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  if (handle != nullptr) {
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    result = resolve_impl<DECORATORS_NONE, true /* external_guard */>(handle);
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  }
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  return result;
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}
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bool JNIHandles::is_weak_global_cleared(jweak handle) {
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  assert(handle != nullptr, "precondition");
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  oop* oop_ptr = weak_global_ptr(handle);
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  oop value = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(oop_ptr);
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  return value == nullptr;
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}
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void JNIHandles::destroy_global(jobject handle) {
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  if (handle != nullptr) {
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    oop* oop_ptr = global_ptr(handle);
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    NativeAccess<>::oop_store(oop_ptr, (oop)nullptr);
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    global_handles()->release(oop_ptr);
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  }
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}
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void JNIHandles::destroy_weak_global(jweak handle) {
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  if (handle != nullptr) {
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    oop* oop_ptr = weak_global_ptr(handle);
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    NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(oop_ptr, (oop)nullptr);
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    weak_global_handles()->release(oop_ptr);
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  }
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}
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void JNIHandles::oops_do(OopClosure* f) {
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  global_handles()->oops_do(f);
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}
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void JNIHandles::weak_oops_do(OopClosure* f) {
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  weak_global_handles()->weak_oops_do(f);
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}
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bool JNIHandles::is_global_storage(const OopStorage* storage) {
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  return _global_handles == storage;
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}
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inline bool is_storage_handle(const OopStorage* storage, const oop* ptr) {
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  return storage->allocation_status(ptr) == OopStorage::ALLOCATED_ENTRY;
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}
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jobjectRefType JNIHandles::handle_type(JavaThread* thread, jobject handle) {
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  assert(handle != nullptr, "precondition");
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  jobjectRefType result = JNIInvalidRefType;
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  if (is_weak_global_tagged(handle)) {
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    if (is_storage_handle(weak_global_handles(), weak_global_ptr(handle))) {
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      result = JNIWeakGlobalRefType;
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    }
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  } else if (is_global_tagged(handle)) {
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    switch (global_handles()->allocation_status(global_ptr(handle))) {
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    case OopStorage::ALLOCATED_ENTRY:
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      result = JNIGlobalRefType;
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      break;
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    case OopStorage::UNALLOCATED_ENTRY:
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      break;                    // Invalid global handle
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    default:
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      ShouldNotReachHere();
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    }
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  } else if (is_local_handle(thread, handle) || is_frame_handle(thread, handle)) {
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    // Not in global storage.  Might be a local handle.
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    result = JNILocalRefType;
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  }
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  return result;
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}
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bool JNIHandles::is_local_handle(JavaThread* thread, jobject handle) {
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  assert(handle != nullptr, "precondition");
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  JNIHandleBlock* block = thread->active_handles();
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  // Look back past possible native calls to jni_PushLocalFrame.
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  while (block != nullptr) {
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    if (block->chain_contains(handle)) {
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      return true;
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    }
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    block = block->pop_frame_link();
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  }
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  return false;
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}
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// Determine if the handle is somewhere in the current thread's stack.
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// We easily can't isolate any particular stack frame the handle might
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// come from, so we'll check the whole stack.
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bool JNIHandles::is_frame_handle(JavaThread* thr, jobject handle) {
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  assert(handle != nullptr, "precondition");
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  // If there is no java frame, then this must be top level code, such
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  // as the java command executable, in which case, this type of handle
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  // is not permitted.
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  return (thr->has_last_Java_frame() &&
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          thr->is_in_stack_range_incl((address)handle, (address)thr->last_Java_sp()));
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}
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bool JNIHandles::is_global_handle(jobject handle) {
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  assert(handle != nullptr, "precondition");
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  return is_global_tagged(handle) && is_storage_handle(global_handles(), global_ptr(handle));
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}
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bool JNIHandles::is_weak_global_handle(jobject handle) {
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  assert(handle != nullptr, "precondition");
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  return is_weak_global_tagged(handle) && is_storage_handle(weak_global_handles(), weak_global_ptr(handle));
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}
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// We assume this is called at a safepoint: no lock is needed.
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void JNIHandles::print_on(outputStream* st) {
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  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
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  st->print_cr("JNI global refs: " SIZE_FORMAT ", weak refs: " SIZE_FORMAT,
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               global_handles()->allocation_count(),
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               weak_global_handles()->allocation_count());
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  st->cr();
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  st->flush();
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}
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void JNIHandles::print() { print_on(tty); }
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class VerifyJNIHandles: public OopClosure {
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public:
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  virtual void do_oop(oop* root) {
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    guarantee(oopDesc::is_oop_or_null(RawAccess<>::oop_load(root)), "Invalid oop");
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  }
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  virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
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};
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void JNIHandles::verify() {
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  VerifyJNIHandles verify_handle;
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  oops_do(&verify_handle);
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  weak_oops_do(&verify_handle);
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}
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// This method is implemented here to avoid circular includes between
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// jniHandles.hpp and thread.hpp.
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bool JNIHandles::current_thread_in_native() {
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  Thread* thread = Thread::current();
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  return (thread->is_Java_thread() &&
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          JavaThread::cast(thread)->thread_state() == _thread_in_native);
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}
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int JNIHandleBlock::_blocks_allocated = 0;
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static inline bool is_tagged_free_list(uintptr_t value) {
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  return (value & 1u) != 0;
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}
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static inline uintptr_t tag_free_list(uintptr_t value) {
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  return value | 1u;
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}
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static inline uintptr_t untag_free_list(uintptr_t value) {
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  return value & ~(uintptr_t)1u;
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}
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// There is a freelist of handles running through the JNIHandleBlock
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// with a tagged next pointer, distinguishing these next pointers from
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// oops. The freelist handling currently relies on the size of oops
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// being the same as a native pointer. If this ever changes, then
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// this freelist handling must change too.
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STATIC_ASSERT(sizeof(oop) == sizeof(uintptr_t));
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#ifdef ASSERT
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void JNIHandleBlock::zap() {
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  // Zap block values
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  _top = 0;
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  for (int index = 0; index < block_size_in_oops; index++) {
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    // NOT using Access here; just bare clobbering to null, since the
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    // block no longer contains valid oops.
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    _handles[index] = 0;
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  }
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}
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#endif // ASSERT
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JNIHandleBlock* JNIHandleBlock::allocate_block(JavaThread* thread, AllocFailType alloc_failmode)  {
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  // The VM thread can allocate a handle block in behalf of another thread during a safepoint.
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  assert(thread == nullptr || thread == Thread::current() || SafepointSynchronize::is_at_safepoint(),
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         "sanity check");
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  JNIHandleBlock* block;
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  // Check the thread-local free list for a block so we don't
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  // have to acquire a mutex.
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  if (thread != nullptr && thread->free_handle_block() != nullptr) {
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    block = thread->free_handle_block();
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    thread->set_free_handle_block(block->_next);
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  } else {
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    // Allocate new block
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    if (alloc_failmode == AllocFailStrategy::RETURN_NULL) {
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      block = new (std::nothrow) JNIHandleBlock();
333
      if (block == nullptr) {
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        return nullptr;
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      }
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    } else {
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      block = new JNIHandleBlock();
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    }
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    Atomic::inc(&_blocks_allocated);
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    block->zap();
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  }
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  block->_top = 0;
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  block->_next = nullptr;
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  block->_pop_frame_link = nullptr;
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  // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
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  debug_only(block->_last = nullptr);
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  debug_only(block->_free_list = nullptr);
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  debug_only(block->_allocate_before_rebuild = -1);
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  return block;
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}
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void JNIHandleBlock::release_block(JNIHandleBlock* block, JavaThread* thread) {
354
  assert(thread == nullptr || thread == Thread::current(), "sanity check");
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  JNIHandleBlock* pop_frame_link = block->pop_frame_link();
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  // Put returned block at the beginning of the thread-local free list.
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  // Note that if thread == nullptr, we use it as an implicit argument that
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  // we _don't_ want the block to be kept on the free_handle_block.
359
  // See for instance JavaThread::exit().
360
  if (thread != nullptr ) {
361
    block->zap();
362
    JNIHandleBlock* freelist = thread->free_handle_block();
363
    block->_pop_frame_link = nullptr;
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    thread->set_free_handle_block(block);
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366
    // Add original freelist to end of chain
367
    if ( freelist != nullptr ) {
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      while ( block->_next != nullptr ) block = block->_next;
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      block->_next = freelist;
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    }
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    block = nullptr;
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  } else {
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    DEBUG_ONLY(block->set_pop_frame_link(nullptr));
374
    while (block != nullptr) {
375
      JNIHandleBlock* next = block->_next;
376
      Atomic::dec(&_blocks_allocated);
377
      assert(block->pop_frame_link() == nullptr, "pop_frame_link should be null");
378
      delete block;
379
      block = next;
380
    }
381
  }
382
  if (pop_frame_link != nullptr) {
383
    // As a sanity check we release blocks pointed to by the pop_frame_link.
384
    // This should never happen (only if PopLocalFrame is not called the
385
    // correct number of times).
386
    release_block(pop_frame_link, thread);
387
  }
388
}
389

390

391
void JNIHandleBlock::oops_do(OopClosure* f) {
392
  JNIHandleBlock* current_chain = this;
393
  // Iterate over chain of blocks, followed by chains linked through the
394
  // pop frame links.
395
  while (current_chain != nullptr) {
396
    for (JNIHandleBlock* current = current_chain; current != nullptr;
397
         current = current->_next) {
398
      assert(current == current_chain || current->pop_frame_link() == nullptr,
399
        "only blocks first in chain should have pop frame link set");
400
      for (int index = 0; index < current->_top; index++) {
401
        uintptr_t* addr = &(current->_handles)[index];
402
        uintptr_t value = *addr;
403
        // traverse heap pointers only, not deleted handles or free list
404
        // pointers
405
        if (value != 0 && !is_tagged_free_list(value)) {
406
          oop* root = (oop*)addr;
407
          f->do_oop(root);
408
        }
409
      }
410
      // the next handle block is valid only if current block is full
411
      if (current->_top < block_size_in_oops) {
412
        break;
413
      }
414
    }
415
    current_chain = current_chain->pop_frame_link();
416
  }
417
}
418

419

420
jobject JNIHandleBlock::allocate_handle(JavaThread* caller, oop obj, AllocFailType alloc_failmode) {
421
  assert(Universe::heap()->is_in(obj), "sanity check");
422
  if (_top == 0) {
423
    // This is the first allocation or the initial block got zapped when
424
    // entering a native function. If we have any following blocks they are
425
    // not valid anymore.
426
    for (JNIHandleBlock* current = _next; current != nullptr;
427
         current = current->_next) {
428
      assert(current->_last == nullptr, "only first block should have _last set");
429
      assert(current->_free_list == nullptr,
430
             "only first block should have _free_list set");
431
      if (current->_top == 0) {
432
        // All blocks after the first clear trailing block are already cleared.
433
#ifdef ASSERT
434
        for (current = current->_next; current != nullptr; current = current->_next) {
435
          assert(current->_top == 0, "trailing blocks must already be cleared");
436
        }
437
#endif
438
        break;
439
      }
440
      current->_top = 0;
441
      current->zap();
442
    }
443
    // Clear initial block
444
    _free_list = nullptr;
445
    _allocate_before_rebuild = 0;
446
    _last = this;
447
    zap();
448
  }
449

450
  // Try last block
451
  if (_last->_top < block_size_in_oops) {
452
    oop* handle = (oop*)&(_last->_handles)[_last->_top++];
453
    *handle = obj;
454
    return (jobject) handle;
455
  }
456

457
  // Try free list
458
  if (_free_list != nullptr) {
459
    oop* handle = (oop*)_free_list;
460
    _free_list = (uintptr_t*) untag_free_list(*_free_list);
461
    *handle = obj;
462
    return (jobject) handle;
463
  }
464
  // Check if unused block follow last
465
  if (_last->_next != nullptr) {
466
    // update last and retry
467
    _last = _last->_next;
468
    return allocate_handle(caller, obj, alloc_failmode);
469
  }
470

471
  // No space available, we have to rebuild free list or expand
472
  if (_allocate_before_rebuild == 0) {
473
      rebuild_free_list();        // updates _allocate_before_rebuild counter
474
  } else {
475
    _last->_next = JNIHandleBlock::allocate_block(caller, alloc_failmode);
476
    if (_last->_next == nullptr) {
477
      return nullptr;
478
    }
479
    _last = _last->_next;
480
    _allocate_before_rebuild--;
481
  }
482
  return allocate_handle(caller, obj, alloc_failmode);  // retry
483
}
484

485
void JNIHandleBlock::rebuild_free_list() {
486
  assert(_allocate_before_rebuild == 0 && _free_list == nullptr, "just checking");
487
  int free = 0;
488
  int blocks = 0;
489
  for (JNIHandleBlock* current = this; current != nullptr; current = current->_next) {
490
    for (int index = 0; index < current->_top; index++) {
491
      uintptr_t* handle = &(current->_handles)[index];
492
      if (*handle == 0) {
493
        // this handle was cleared out by a delete call, reuse it
494
        *handle = _free_list == nullptr ? 0 : tag_free_list((uintptr_t)_free_list);
495
        _free_list = handle;
496
        free++;
497
      }
498
    }
499
    // we should not rebuild free list if there are unused handles at the end
500
    assert(current->_top == block_size_in_oops, "just checking");
501
    blocks++;
502
  }
503
  // Heuristic: if more than half of the handles are free we rebuild next time
504
  // as well, otherwise we append a corresponding number of new blocks before
505
  // attempting a free list rebuild again.
506
  int total = blocks * block_size_in_oops;
507
  int extra = total - 2*free;
508
  if (extra > 0) {
509
    // Not as many free handles as we would like - compute number of new blocks to append
510
    _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
511
  }
512
}
513

514

515
bool JNIHandleBlock::contains(jobject handle) const {
516
  return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
517
}
518

519

520
bool JNIHandleBlock::chain_contains(jobject handle) const {
521
  for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != nullptr; current = current->_next) {
522
    if (current->contains(handle)) {
523
      return true;
524
    }
525
  }
526
  return false;
527
}
528