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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef gc_GCParallelTask_h
#define gc_GCParallelTask_h
#include "mozilla/LinkedList.h"
#include "mozilla/TimeStamp.h"
#include <utility>
#include "js/TypeDecls.h"
#include "js/Utility.h"
#include "threading/ProtectedData.h"
#include "vm/HelperThreadTask.h"
#define JS_MEMBER_FN_PTR_TYPE(ClassT, ReturnT, /* ArgTs */...) \
ReturnT (ClassT::*)(__VA_ARGS__)
#define JS_CALL_MEMBER_FN_PTR(Receiver, Ptr, /* Args */...) \
namespace js {
namespace gc {
class GCRuntime;
class AutoLockHelperThreadState;
class HelperThread;
// A generic task used to dispatch work to the helper thread system.
// Users override the pure-virtual run() method.
class GCParallelTask : public mozilla::LinkedListElement<GCParallelTask>,
public HelperThreadTask {
gc::GCRuntime* const gc;
// The state of the parallel computation.
enum class State {
// The task is idle. Either start() has not been called or join() has
// returned.
// The task has been started but has not yet begun running on a helper
// thread.
// The task is currently running on a helper thread.
// The task has finished running but has not yet been joined by the main
// thread.
UnprotectedData<State> state_;
// Amount of time this task took to execute.
MainThreadOrGCTaskData<mozilla::TimeDuration> duration_;
explicit GCParallelTask(const GCParallelTask&) = delete;
// A flag to signal a request for early completion of the off-thread task.
mozilla::Atomic<bool, mozilla::MemoryOrdering::ReleaseAcquire> cancel_;
explicit GCParallelTask(gc::GCRuntime* gc)
: gc(gc), state_(State::Idle), duration_(nullptr), cancel_(false) {}
GCParallelTask(GCParallelTask&& other)
: gc(other.gc),
cancel_(false) {}
// Derived classes must override this to ensure that join() gets called
// before members get destructed.
virtual ~GCParallelTask();
// Time spent in the most recent invocation of this task.
mozilla::TimeDuration duration() const { return duration_; }
// The simple interface to a parallel task works exactly like pthreads.
void start();
void join();
// If multiple tasks are to be started or joined at once, it is more
// efficient to take the helper thread lock once and use these methods.
void startWithLockHeld(AutoLockHelperThreadState& lock);
void joinWithLockHeld(AutoLockHelperThreadState& lock);
void joinRunningOrFinishedTask(AutoLockHelperThreadState& lock);
// Instead of dispatching to a helper, run the task on the current thread.
void runFromMainThread();
// If the task is not already running, either start it or run it on the main
// thread if that fails.
void startOrRunIfIdle(AutoLockHelperThreadState& lock);
// Cancel a dispatched task before it started executing.
void cancelDispatchedTask(AutoLockHelperThreadState& lock);
// Set the cancel flag and wait for the task to finish.
void cancelAndWait() {
cancel_ = true;
// Report whether the task is idle. This means either before start() has been
// called or after join() has been called.
bool isIdle() const;
bool isIdle(const AutoLockHelperThreadState& lock) const {
return state_ == State::Idle;
// Report whether the task has been started. This means after start() has been
// called but before the task has run to completion. The task may not yet have
// started running.
bool wasStarted() const;
bool wasStarted(const AutoLockHelperThreadState& lock) const {
return isDispatched(lock) || isRunning(lock);
bool isDispatched(const AutoLockHelperThreadState& lock) const {
return state_ == State::Dispatched;
// Override this method to provide the task's functionality.
virtual void run(AutoLockHelperThreadState& lock) = 0;
void assertIdle() const {
// Don't lock here because that adds extra synchronization in debug
// builds that may hide bugs. There's no race if the assertion passes.
MOZ_ASSERT(state_ == State::Idle);
bool isRunning(const AutoLockHelperThreadState& lock) const {
return state_ == State::Running;
bool isFinished(const AutoLockHelperThreadState& lock) const {
return state_ == State::Finished;
void setDispatched(const AutoLockHelperThreadState& lock) {
state_ = State::Dispatched;
void setRunning(const AutoLockHelperThreadState& lock) {
state_ = State::Running;
void setFinished(const AutoLockHelperThreadState& lock) {
state_ = State::Finished;
void setIdle(const AutoLockHelperThreadState& lock) {
MOZ_ASSERT(isDispatched(lock) || isFinished(lock));
state_ = State::Idle;
void runTask(AutoLockHelperThreadState& lock);
// Implement the HelperThreadTask interface.
ThreadType threadType() override {
void runHelperThreadTask(AutoLockHelperThreadState& locked) override;
} /* namespace js */
#endif /* gc_GCParallelTask_h */