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// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#include "vm/thread_interrupter.h"
#include "vm/flags.h"
#include "vm/lockers.h"
#include "vm/os.h"
#include "vm/simulator.h"
namespace dart {
#ifndef PRODUCT
// Notes:
//
// The ThreadInterrupter interrupts all threads actively running isolates once
// per interrupt period (default is 1 millisecond). While the thread is
// interrupted, the thread's interrupt callback is invoked. Callbacks cannot
// rely on being executed on the interrupted thread.
//
// There are two mechanisms used to interrupt a thread. The first, used on Linux
// and Android, is SIGPROF. The second, used on Windows, Fuchsia, Mac and iOS,
// is explicit suspend and resume thread system calls. (Although Mac supports
// SIGPROF, when the process is attached to lldb, it becomes unusably slow, and
// signal masking is unreliable across fork-exec.) Signal delivery forbids
// taking locks and allocating memory (which takes a lock). Explicit suspend and
// resume means that the interrupt callback will not be executing on the
// interrupted thread, making it meaningless to access TLS from within the
// thread interrupt callback. Combining these limitations, thread interrupt
// callbacks are forbidden from:
//
// * Accessing TLS.
// * Allocating memory.
// * Taking a lock.
//
// The ThreadInterrupter has a single monitor (monitor_). This monitor is used
// to synchronize startup, shutdown, and waking up from a deep sleep.
//
DEFINE_FLAG(bool, trace_thread_interrupter, false, "Trace thread interrupter");
bool ThreadInterrupter::initialized_ = false;
bool ThreadInterrupter::shutdown_ = false;
bool ThreadInterrupter::thread_running_ = false;
bool ThreadInterrupter::woken_up_ = false;
ThreadJoinId ThreadInterrupter::interrupter_thread_id_ =
OSThread::kInvalidThreadJoinId;
Monitor* ThreadInterrupter::monitor_ = nullptr;
intptr_t ThreadInterrupter::interrupt_period_ = 1000;
intptr_t ThreadInterrupter::current_wait_time_ = Monitor::kNoTimeout;
void ThreadInterrupter::Init() {
ASSERT(!initialized_);
if (monitor_ == nullptr) {
monitor_ = new Monitor();
}
ASSERT(monitor_ != nullptr);
initialized_ = true;
shutdown_ = false;
}
void ThreadInterrupter::Startup() {
ASSERT(initialized_);
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter starting up.\n");
}
ASSERT(interrupter_thread_id_ == OSThread::kInvalidThreadJoinId);
{
MonitorLocker startup_ml(monitor_);
OSThread::Start("Dart Profiler ThreadInterrupter", ThreadMain, 0);
while (!thread_running_) {
startup_ml.Wait();
}
}
ASSERT(interrupter_thread_id_ != OSThread::kInvalidThreadJoinId);
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter running.\n");
}
}
void ThreadInterrupter::Cleanup() {
{
MonitorLocker shutdown_ml(monitor_);
if (shutdown_) {
// Already shutdown.
return;
}
shutdown_ = true;
// Notify.
shutdown_ml.Notify();
ASSERT(initialized_);
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter shutting down.\n");
}
}
// Join the thread.
ASSERT(interrupter_thread_id_ != OSThread::kInvalidThreadJoinId);
OSThread::Join(interrupter_thread_id_);
interrupter_thread_id_ = OSThread::kInvalidThreadJoinId;
initialized_ = false;
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter shut down.\n");
}
}
// Delay between interrupts.
void ThreadInterrupter::SetInterruptPeriod(intptr_t period) {
if (!initialized_) {
// Profiler may not be enabled.
return;
}
MonitorLocker ml(monitor_);
if (shutdown_) {
return;
}
ASSERT(initialized_);
ASSERT(period > 0);
interrupt_period_ = period;
}
void ThreadInterrupter::WakeUp() {
if (monitor_ == nullptr) {
// Early call.
return;
}
{
MonitorLocker ml(monitor_);
if (shutdown_) {
// Late call
return;
}
if (!initialized_) {
// Early call.
return;
}
woken_up_ = true;
if (!InDeepSleep()) {
// No need to notify, regularly waking up.
return;
}
// Notify the interrupter to wake it from its deep sleep.
ml.Notify();
}
}
void ThreadInterrupter::ThreadMain(uword parameters) {
ASSERT(initialized_);
InstallSignalHandler();
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter thread running.\n");
}
{
// Signal to main thread we are ready.
MonitorLocker startup_ml(monitor_);
OSThread* os_thread = OSThread::Current();
ASSERT(os_thread != nullptr);
interrupter_thread_id_ = OSThread::GetCurrentThreadJoinId(os_thread);
thread_running_ = true;
startup_ml.Notify();
}
{
intptr_t interrupted_thread_count = 0;
MonitorLocker wait_ml(monitor_);
current_wait_time_ = interrupt_period_;
while (!shutdown_) {
intptr_t r = wait_ml.WaitMicros(current_wait_time_);
if (shutdown_) {
break;
}
if ((r == Monitor::kNotified) && InDeepSleep()) {
// Woken up from deep sleep.
ASSERT(interrupted_thread_count == 0);
// Return to regular interrupts.
current_wait_time_ = interrupt_period_;
} else if (current_wait_time_ != interrupt_period_) {
// The interrupt period may have been updated via the service protocol.
current_wait_time_ = interrupt_period_;
}
// Reset count before interrupting any threads.
interrupted_thread_count = 0;
// Temporarily drop the monitor while we interrupt threads.
wait_ml.Exit();
{
OSThreadIterator it;
while (it.HasNext()) {
OSThread* thread = it.Next();
if (thread->ThreadInterruptsEnabled()) {
interrupted_thread_count++;
InterruptThread(thread);
}
}
}
// Take the monitor lock again.
wait_ml.Enter();
// Now that we have the lock, check if we were signaled to wake up while
// interrupting threads.
if (!woken_up_ && (interrupted_thread_count == 0)) {
// No threads were interrupted and we were not signaled to interrupt
// new threads. In order to reduce unnecessary CPU load, we will wait
// until we are notified before attempting to interrupt again.
current_wait_time_ = Monitor::kNoTimeout;
continue;
}
woken_up_ = false;
ASSERT(current_wait_time_ != Monitor::kNoTimeout);
}
}
RemoveSignalHandler();
if (FLAG_trace_thread_interrupter) {
OS::PrintErr("ThreadInterrupter thread exiting.\n");
}
{
// Signal to main thread we are exiting.
MonitorLocker shutdown_ml(monitor_);
thread_running_ = false;
shutdown_ml.Notify();
}
}
#if !defined(DART_HOST_OS_ANDROID)
void* ThreadInterrupter::PrepareCurrentThread() {
return nullptr;
}
void ThreadInterrupter::CleanupCurrentThreadState(void* state) {}
#endif
#endif // !PRODUCT
} // namespace dart