jdk

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/*
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 * Copyright (c) 1998, 2024, 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 "compiler/compileBroker.hpp"
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#include "gc/shared/collectedHeap.hpp"
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#include "jfr/jfrEvents.hpp"
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#include "jfr/support/jfrThreadId.hpp"
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#include "logging/log.hpp"
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#include "logging/logStream.hpp"
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#include "logging/logConfiguration.hpp"
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#include "memory/resourceArea.hpp"
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#include "memory/universe.hpp"
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#include "oops/oop.inline.hpp"
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#include "oops/verifyOopClosure.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/cpuTimeCounters.hpp"
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#include "runtime/handles.inline.hpp"
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#include "runtime/interfaceSupport.inline.hpp"
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#include "runtime/javaThread.inline.hpp"
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#include "runtime/jniHandles.hpp"
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#include "runtime/mutexLocker.hpp"
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#include "runtime/os.hpp"
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#include "runtime/perfData.hpp"
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#include "runtime/safepoint.hpp"
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#include "runtime/synchronizer.hpp"
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#include "runtime/timerTrace.hpp"
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#include "runtime/vmThread.hpp"
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#include "runtime/vmOperations.hpp"
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#include "utilities/dtrace.hpp"
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#include "utilities/events.hpp"
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#include "utilities/vmError.hpp"
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55

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//------------------------------------------------------------------------------------------------------------------
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// Timeout machinery
58

59
void VMOperationTimeoutTask::task() {
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  assert(AbortVMOnVMOperationTimeout, "only if enabled");
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  if (is_armed()) {
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    jlong delay = nanos_to_millis(os::javaTimeNanos() - _arm_time);
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    if (delay > AbortVMOnVMOperationTimeoutDelay) {
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      fatal("%s VM operation took too long: " JLONG_FORMAT " ms elapsed since VM-op start (timeout: " INTX_FORMAT " ms)",
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            _vm_op_name, delay, AbortVMOnVMOperationTimeoutDelay);
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    }
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  }
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}
69

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bool VMOperationTimeoutTask::is_armed() {
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  return Atomic::load_acquire(&_armed) != 0;
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}
73

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void VMOperationTimeoutTask::arm(const char* vm_op_name) {
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  _vm_op_name = vm_op_name;
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  _arm_time = os::javaTimeNanos();
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  Atomic::release_store_fence(&_armed, 1);
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}
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void VMOperationTimeoutTask::disarm() {
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  Atomic::release_store_fence(&_armed, 0);
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  // The two stores to `_armed` are counted in VM-op, but they should be
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  // insignificant compared to the actual VM-op duration.
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  jlong vm_op_duration = nanos_to_millis(os::javaTimeNanos() - _arm_time);
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  // Repeat the timeout-check logic on the VM thread, because
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  // VMOperationTimeoutTask might miss the arm-disarm window depending on
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  // the scheduling.
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  if (vm_op_duration > AbortVMOnVMOperationTimeoutDelay) {
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    fatal("%s VM operation took too long: completed in " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
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          _vm_op_name, vm_op_duration, AbortVMOnVMOperationTimeoutDelay);
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  }
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  _vm_op_name = nullptr;
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}
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//------------------------------------------------------------------------------------------------------------------
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// Implementation of VMThread stuff
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static VM_SafepointALot safepointALot_op;
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static VM_ForceSafepoint no_op;
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bool              VMThread::_should_terminate   = false;
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bool              VMThread::_terminated         = false;
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Monitor*          VMThread::_terminate_lock     = nullptr;
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VMThread*         VMThread::_vm_thread          = nullptr;
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VM_Operation*     VMThread::_cur_vm_operation   = nullptr;
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VM_Operation*     VMThread::_next_vm_operation  = &no_op; // Prevent any thread from setting an operation until VM thread is ready.
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PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = nullptr;
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VMOperationTimeoutTask* VMThread::_timeout_task = nullptr;
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112

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void VMThread::create() {
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  assert(vm_thread() == nullptr, "we can only allocate one VMThread");
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  _vm_thread = new VMThread();
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  if (AbortVMOnVMOperationTimeout) {
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    // Make sure we call the timeout task frequently enough, but not too frequent.
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    // Try to make the interval 10% of the timeout delay, so that we miss the timeout
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    // by those 10% at max. Periodic task also expects it to fit min/max intervals.
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    size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
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    interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
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    interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
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    interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
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    _timeout_task = new VMOperationTimeoutTask(interval);
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    _timeout_task->enroll();
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  } else {
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    assert(_timeout_task == nullptr, "sanity");
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  }
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  _terminate_lock = new Monitor(Mutex::nosafepoint, "VMThreadTerminate_lock");
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  if (UsePerfData) {
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    // jvmstat performance counters
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    JavaThread* THREAD = JavaThread::current(); // For exception macros.
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    _perf_accumulated_vm_operation_time =
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                 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
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                                                 PerfData::U_Ticks, CHECK);
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    CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::vm);
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  }
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}
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VMThread::VMThread() : NamedThread(), _is_running(false) {
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  set_name("VM Thread");
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}
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void VMThread::destroy() {
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  _vm_thread = nullptr;      // VM thread is gone
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}
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static VM_Halt halt_op;
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void VMThread::run() {
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  assert(this == vm_thread(), "check");
156

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  // Notify_lock wait checks on is_running() to rewait in
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  // case of spurious wakeup, it should wait on the last
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  // value set prior to the notify
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  Atomic::store(&_is_running, true);
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  {
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    MutexLocker ml(Notify_lock);
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    Notify_lock->notify();
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  }
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  // Notify_lock is destroyed by Threads::create_vm()
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  int prio = (VMThreadPriority == -1)
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    ? os::java_to_os_priority[NearMaxPriority]
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    : VMThreadPriority;
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  // Note that I cannot call os::set_priority because it expects Java
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  // priorities and I am *explicitly* using OS priorities so that it's
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  // possible to set the VM thread priority higher than any Java thread.
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  os::set_native_priority( this, prio );
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176
  // Wait for VM_Operations until termination
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  this->loop();
178

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  // Note the intention to exit before safepointing.
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  // 6295565  This has the effect of waiting for any large tty
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  // outputs to finish.
182
  if (xtty != nullptr) {
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    ttyLocker ttyl;
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    xtty->begin_elem("destroy_vm");
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    xtty->stamp();
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    xtty->end_elem();
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    assert(should_terminate(), "termination flag must be set");
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  }
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  // 4526887 let VM thread exit at Safepoint
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  _cur_vm_operation = &halt_op;
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  SafepointSynchronize::begin();
193

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  if (VerifyBeforeExit) {
195
    HandleMark hm(VMThread::vm_thread());
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    // Among other things, this ensures that Eden top is correct.
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    Universe::heap()->prepare_for_verify();
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    // Silent verification so as not to pollute normal output,
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    // unless we really asked for it.
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    Universe::verify();
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  }
202

203
  CompileBroker::set_should_block();
204

205
  // wait for threads (compiler threads or daemon threads) in the
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  // _thread_in_native state to block.
207
  VM_Exit::wait_for_threads_in_native_to_block();
208

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  // The ObjectMonitor subsystem uses perf counters so do this before
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  // we signal that the VM thread is gone. We don't want to run afoul
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  // of perfMemory_exit() in exit_globals().
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  ObjectSynchronizer::do_final_audit_and_print_stats();
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  // signal other threads that VM process is gone
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  {
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    // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
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    // VM thread to enter any lock at Safepoint as long as its _owner is null.
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    // If that happens after _terminate_lock->wait() has unset _owner
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    // but before it actually drops the lock and waits, the notification below
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    // may get lost and we will have a hang. To avoid this, we need to use
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    // Mutex::lock_without_safepoint_check().
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    MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
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    _terminated = true;
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    ml.notify();
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  }
226

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  // We are now racing with the VM termination being carried out in
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  // another thread, so we don't "delete this". Numerous threads don't
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  // get deleted when the VM terminates
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}
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// Notify the VMThread that the last non-daemon JavaThread has terminated,
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// and wait until operation is performed.
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void VMThread::wait_for_vm_thread_exit() {
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  assert(JavaThread::current()->is_terminated(), "Should be terminated");
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  {
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    MonitorLocker mu(VMOperation_lock);
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    _should_terminate = true;
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    mu.notify_all();
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  }
243

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  // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
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  // because this thread has been removed from the threads list. But anything
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  // that could get blocked by Safepoint should not be used after this point,
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  // otherwise we will hang, since there is no one can end the safepoint.
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  // Wait until VM thread is terminated
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  // Note: it should be OK to use Terminator_lock here. But this is called
251
  // at a very delicate time (VM shutdown) and we are operating in non- VM
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  // thread at Safepoint. It's safer to not share lock with other threads.
253
  {
254
    MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
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    while (!VMThread::is_terminated()) {
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      ml.wait();
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    }
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  }
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}
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static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
262
  assert(event != nullptr, "invariant");
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  assert(op != nullptr, "invariant");
264
  const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
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  event->set_operation(op->type());
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  event->set_safepoint(evaluate_at_safepoint);
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  event->set_blocking(true);
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  event->set_caller(JFR_THREAD_ID(op->calling_thread()));
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  event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
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  event->commit();
271
}
272

273
void VMThread::evaluate_operation(VM_Operation* op) {
274
  ResourceMark rm;
275

276
  {
277
    PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
278
    HOTSPOT_VMOPS_BEGIN(
279
                     (char *) op->name(), strlen(op->name()),
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                     op->evaluate_at_safepoint() ? 0 : 1);
281

282
    EventExecuteVMOperation event;
283
    op->evaluate();
284
    if (event.should_commit()) {
285
      post_vm_operation_event(&event, op);
286
    }
287

288
    HOTSPOT_VMOPS_END(
289
                     (char *) op->name(), strlen(op->name()),
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                     op->evaluate_at_safepoint() ? 0 : 1);
291
  }
292

293
  if (UsePerfData && os::is_thread_cpu_time_supported()) {
294
    assert(Thread::current() == this, "Must be called from VM thread");
295
    // Update vm_thread_cpu_time after each VM operation.
296
    ThreadTotalCPUTimeClosure tttc(CPUTimeGroups::CPUTimeType::vm);
297
    tttc.do_thread(this);
298
  }
299
}
300

301
class HandshakeALotClosure : public HandshakeClosure {
302
 public:
303
  HandshakeALotClosure() : HandshakeClosure("HandshakeALot") {}
304
  void do_thread(Thread* thread) {
305
#ifdef ASSERT
306
    JavaThread::cast(thread)->verify_states_for_handshake();
307
#endif
308
  }
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};
310

311
bool VMThread::handshake_or_safepoint_alot() {
312
  assert(_cur_vm_operation == nullptr, "should not have an op yet");
313
  assert(_next_vm_operation == nullptr, "should not have an op yet");
314
  if (!HandshakeALot && !SafepointALot) {
315
    return false;
316
  }
317
  static jlong last_alot_ms = 0;
318
  jlong now_ms = nanos_to_millis(os::javaTimeNanos());
319
  // If HandshakeALot or SafepointALot are set, but GuaranteedSafepointInterval is explicitly
320
  // set to 0 on the command line, we emit the operation if it's been more than a second
321
  // since the last one.
322
  jlong interval = GuaranteedSafepointInterval != 0 ? GuaranteedSafepointInterval : 1000;
323
  jlong deadline_ms = interval + last_alot_ms;
324
  if (now_ms > deadline_ms) {
325
    last_alot_ms = now_ms;
326
    return true;
327
  }
328
  return false;
329
}
330

331
bool VMThread::set_next_operation(VM_Operation *op) {
332
  if (_next_vm_operation != nullptr) {
333
    return false;
334
  }
335
  log_debug(vmthread)("Adding VM operation: %s", op->name());
336

337
  _next_vm_operation = op;
338

339
  HOTSPOT_VMOPS_REQUEST(
340
                   (char *) op->name(), strlen(op->name()),
341
                   op->evaluate_at_safepoint() ? 0 : 1);
342
  return true;
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}
344

345
void VMThread::wait_until_executed(VM_Operation* op) {
346
  MonitorLocker ml(VMOperation_lock,
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                   Thread::current()->is_Java_thread() ?
348
                     Mutex::_safepoint_check_flag :
349
                     Mutex::_no_safepoint_check_flag);
350
  {
351
    TraceTime timer("Installing VM operation", TRACETIME_LOG(Trace, vmthread));
352
    while (true) {
353
      if (VMThread::vm_thread()->set_next_operation(op)) {
354
        ml.notify_all();
355
        break;
356
      }
357
      // Wait to install this operation as the next operation in the VM Thread
358
      log_trace(vmthread)("A VM operation already set, waiting");
359
      ml.wait();
360
    }
361
  }
362
  {
363
    // Wait until the operation has been processed
364
    TraceTime timer("Waiting for VM operation to be completed", TRACETIME_LOG(Trace, vmthread));
365
    // _next_vm_operation is cleared holding VMOperation_lock after it has been
366
    // executed. We wait until _next_vm_operation is not our op.
367
    while (_next_vm_operation == op) {
368
      // VM Thread can process it once we unlock the mutex on wait.
369
      ml.wait();
370
    }
371
  }
372
}
373

374
static void self_destruct_if_needed() {
375
  // Support for self destruction
376
  if ((SelfDestructTimer != 0.0) && !VMError::is_error_reported() &&
377
      (os::elapsedTime() > SelfDestructTimer * 60.0)) {
378
    tty->print_cr("VM self-destructed");
379
    os::exit(-1);
380
  }
381
}
382

383
void VMThread::inner_execute(VM_Operation* op) {
384
  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
385

386
  VM_Operation* prev_vm_operation = nullptr;
387
  if (_cur_vm_operation != nullptr) {
388
    // Check that the VM operation allows nested VM operation.
389
    // This is normally not the case, e.g., the compiler
390
    // does not allow nested scavenges or compiles.
391
    if (!_cur_vm_operation->allow_nested_vm_operations()) {
392
      fatal("Unexpected nested VM operation %s requested by operation %s",
393
            op->name(), _cur_vm_operation->name());
394
    }
395
    op->set_calling_thread(_cur_vm_operation->calling_thread());
396
    prev_vm_operation = _cur_vm_operation;
397
  }
398

399
  _cur_vm_operation = op;
400

401
  HandleMark hm(VMThread::vm_thread());
402

403
  const char* const cause = op->cause();
404
  EventMarkVMOperation em("Executing %sVM operation: %s%s%s%s",
405
      prev_vm_operation != nullptr ? "nested " : "",
406
      op->name(),
407
      cause != nullptr ? " (" : "",
408
      cause != nullptr ? cause : "",
409
      cause != nullptr ? ")" : "");
410

411
  log_debug(vmthread)("Evaluating %s %s VM operation: %s",
412
                       prev_vm_operation != nullptr ? "nested" : "",
413
                      _cur_vm_operation->evaluate_at_safepoint() ? "safepoint" : "non-safepoint",
414
                      _cur_vm_operation->name());
415

416
  bool end_safepoint = false;
417
  bool has_timeout_task = (_timeout_task != nullptr);
418
  if (_cur_vm_operation->evaluate_at_safepoint() &&
419
      !SafepointSynchronize::is_at_safepoint()) {
420
    SafepointSynchronize::begin();
421
    if (has_timeout_task) {
422
      _timeout_task->arm(_cur_vm_operation->name());
423
    }
424
    end_safepoint = true;
425
  }
426

427
  evaluate_operation(_cur_vm_operation);
428

429
  if (end_safepoint) {
430
    if (has_timeout_task) {
431
      _timeout_task->disarm();
432
    }
433
    SafepointSynchronize::end();
434
  }
435

436
  _cur_vm_operation = prev_vm_operation;
437
}
438

439
void VMThread::wait_for_operation() {
440
  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
441
  MonitorLocker ml_op_lock(VMOperation_lock, Mutex::_no_safepoint_check_flag);
442

443
  // Clear previous operation.
444
  // On first call this clears a dummy place-holder.
445
  _next_vm_operation = nullptr;
446
  // Notify operation is done and notify a next operation can be installed.
447
  ml_op_lock.notify_all();
448

449
  while (!should_terminate()) {
450
    self_destruct_if_needed();
451
    if (_next_vm_operation != nullptr) {
452
      return;
453
    }
454
    if (handshake_or_safepoint_alot()) {
455
      if (HandshakeALot) {
456
        MutexUnlocker mul(VMOperation_lock);
457
        HandshakeALotClosure hal_cl;
458
        Handshake::execute(&hal_cl);
459
      }
460
      // When we unlocked above someone might have setup a new op.
461
      if (_next_vm_operation != nullptr) {
462
        return;
463
      }
464
      if (SafepointALot) {
465
        _next_vm_operation = &safepointALot_op;
466
        return;
467
      }
468
    }
469
    assert(_next_vm_operation == nullptr, "Must be");
470
    assert(_cur_vm_operation  == nullptr, "Must be");
471

472
    // We didn't find anything to execute, notify any waiter so they can install an op.
473
    ml_op_lock.notify_all();
474
    ml_op_lock.wait(GuaranteedSafepointInterval);
475
  }
476
}
477

478
void VMThread::loop() {
479
  assert(_cur_vm_operation == nullptr, "no current one should be executing");
480

481
  SafepointSynchronize::init(_vm_thread);
482

483
  // Need to set a calling thread for ops not passed
484
  // via the normal way.
485
  no_op.set_calling_thread(_vm_thread);
486
  safepointALot_op.set_calling_thread(_vm_thread);
487

488
  while (true) {
489
    if (should_terminate()) break;
490
    wait_for_operation();
491
    if (should_terminate()) break;
492
    assert(_next_vm_operation != nullptr, "Must have one");
493
    inner_execute(_next_vm_operation);
494
  }
495
}
496

497
// A SkipGCALot object is used to elide the usual effect of gc-a-lot
498
// over a section of execution by a thread. Currently, it's used only to
499
// prevent re-entrant calls to GC.
500
class SkipGCALot : public StackObj {
501
  private:
502
   bool _saved;
503
   Thread* _t;
504

505
  public:
506
#ifdef ASSERT
507
    SkipGCALot(Thread* t) : _t(t) {
508
      _saved = _t->skip_gcalot();
509
      _t->set_skip_gcalot(true);
510
    }
511

512
    ~SkipGCALot() {
513
      assert(_t->skip_gcalot(), "Save-restore protocol invariant");
514
      _t->set_skip_gcalot(_saved);
515
    }
516
#else
517
    SkipGCALot(Thread* t) { }
518
    ~SkipGCALot() { }
519
#endif
520
};
521

522
void VMThread::execute(VM_Operation* op) {
523
  Thread* t = Thread::current();
524

525
  if (t->is_VM_thread()) {
526
    op->set_calling_thread(t);
527
    ((VMThread*)t)->inner_execute(op);
528
    return;
529
  }
530

531
  // Avoid re-entrant attempts to gc-a-lot
532
  SkipGCALot sgcalot(t);
533

534
  // JavaThread or WatcherThread
535
  if (t->is_Java_thread()) {
536
    JavaThread::cast(t)->check_for_valid_safepoint_state();
537
  }
538

539
  // New request from Java thread, evaluate prologue
540
  if (!op->doit_prologue()) {
541
    return;   // op was cancelled
542
  }
543

544
  op->set_calling_thread(t);
545

546
  wait_until_executed(op);
547

548
  op->doit_epilogue();
549
}
550

551
void VMThread::verify() {
552
  oops_do(&VerifyOopClosure::verify_oop, nullptr);
553
}
554