gecko-dev/xpcom/threads/TaskQueue.cpp

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7.3 KiB
C++

/* -*- 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 http://mozilla.org/MPL/2.0/. */
#include "mozilla/TaskQueue.h"
#include "nsIEventTarget.h"
#include "nsThreadUtils.h"
namespace mozilla {
class TaskQueue::EventTargetWrapper final : public nsIEventTarget
{
RefPtr<TaskQueue> mTaskQueue;
~EventTargetWrapper()
{
}
public:
explicit EventTargetWrapper(TaskQueue* aTaskQueue)
: mTaskQueue(aTaskQueue)
{
MOZ_ASSERT(mTaskQueue);
}
NS_IMETHOD
DispatchFromScript(nsIRunnable* aEvent, uint32_t aFlags) override
{
nsCOMPtr<nsIRunnable> ref = aEvent;
return Dispatch(ref.forget(), aFlags);
}
NS_IMETHOD
Dispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags) override
{
nsCOMPtr<nsIRunnable> runnable = aEvent;
MonitorAutoLock mon(mTaskQueue->mQueueMonitor);
return mTaskQueue->DispatchLocked(/* passed by ref */runnable,
DontAssertDispatchSuccess,
NormalDispatch);
}
NS_IMETHOD
DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t aFlags) override
{
return NS_ERROR_NOT_IMPLEMENTED;
}
NS_IMETHOD
IsOnCurrentThread(bool* aResult) override
{
*aResult = mTaskQueue->IsCurrentThreadIn();
return NS_OK;
}
NS_DECL_THREADSAFE_ISUPPORTS
};
NS_IMPL_ISUPPORTS(TaskQueue::EventTargetWrapper, nsIEventTarget)
TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
const char* aName,
bool aRequireTailDispatch)
: AbstractThread(aRequireTailDispatch)
, mTarget(aTarget)
, mQueueMonitor("TaskQueue::Queue")
, mTailDispatcher(nullptr)
, mIsRunning(false)
, mIsShutdown(false)
, mName(aName)
{
MOZ_COUNT_CTOR(TaskQueue);
}
TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
bool aSupportsTailDispatch)
: TaskQueue(Move(aTarget), "Unnamed", aSupportsTailDispatch)
{
}
TaskQueue::~TaskQueue()
{
MonitorAutoLock mon(mQueueMonitor);
MOZ_ASSERT(mIsShutdown);
MOZ_COUNT_DTOR(TaskQueue);
}
TaskDispatcher&
TaskQueue::TailDispatcher()
{
MOZ_ASSERT(IsCurrentThreadIn());
MOZ_ASSERT(mTailDispatcher);
return *mTailDispatcher;
}
// Note aRunnable is passed by ref to support conditional ownership transfer.
// See Dispatch() in TaskQueue.h for more details.
nsresult
TaskQueue::DispatchLocked(nsCOMPtr<nsIRunnable>& aRunnable,
DispatchFailureHandling aFailureHandling,
DispatchReason aReason)
{
mQueueMonitor.AssertCurrentThreadOwns();
if (mIsShutdown) {
return NS_ERROR_FAILURE;
}
AbstractThread* currentThread;
if (aReason != TailDispatch && (currentThread = GetCurrent()) && RequiresTailDispatch(currentThread)) {
currentThread->TailDispatcher().AddTask(this, aRunnable.forget(), aFailureHandling);
return NS_OK;
}
mTasks.push(aRunnable.forget());
if (mIsRunning) {
return NS_OK;
}
RefPtr<nsIRunnable> runner(new Runner(this));
nsresult rv = mTarget->Dispatch(runner.forget(), NS_DISPATCH_NORMAL);
if (NS_FAILED(rv)) {
NS_WARNING("Failed to dispatch runnable to run TaskQueue");
return rv;
}
mIsRunning = true;
return NS_OK;
}
void
TaskQueue::AwaitIdle()
{
MonitorAutoLock mon(mQueueMonitor);
AwaitIdleLocked();
}
void
TaskQueue::AwaitIdleLocked()
{
// Make sure there are no tasks for this queue waiting in the caller's tail
// dispatcher.
MOZ_ASSERT_IF(AbstractThread::GetCurrent(),
!AbstractThread::GetCurrent()->HasTailTasksFor(this));
mQueueMonitor.AssertCurrentThreadOwns();
MOZ_ASSERT(mIsRunning || mTasks.empty());
while (mIsRunning) {
mQueueMonitor.Wait();
}
}
void
TaskQueue::AwaitShutdownAndIdle()
{
MOZ_ASSERT(!IsCurrentThreadIn());
// Make sure there are no tasks for this queue waiting in the caller's tail
// dispatcher.
MOZ_ASSERT_IF(AbstractThread::GetCurrent(),
!AbstractThread::GetCurrent()->HasTailTasksFor(this));
MonitorAutoLock mon(mQueueMonitor);
while (!mIsShutdown) {
mQueueMonitor.Wait();
}
AwaitIdleLocked();
}
RefPtr<ShutdownPromise>
TaskQueue::BeginShutdown()
{
// Dispatch any tasks for this queue waiting in the caller's tail dispatcher,
// since this is the last opportunity to do so.
if (AbstractThread* currentThread = AbstractThread::GetCurrent()) {
currentThread->TailDispatchTasksFor(this);
}
MonitorAutoLock mon(mQueueMonitor);
mIsShutdown = true;
RefPtr<ShutdownPromise> p = mShutdownPromise.Ensure(__func__);
MaybeResolveShutdown();
mon.NotifyAll();
return p;
}
bool
TaskQueue::IsEmpty()
{
MonitorAutoLock mon(mQueueMonitor);
return mTasks.empty();
}
uint32_t
TaskQueue::ImpreciseLengthForHeuristics()
{
MonitorAutoLock mon(mQueueMonitor);
return mTasks.size();
}
bool
TaskQueue::IsCurrentThreadIn()
{
bool in = NS_GetCurrentThread() == mRunningThread;
return in;
}
already_AddRefed<nsIEventTarget>
TaskQueue::WrapAsEventTarget()
{
nsCOMPtr<nsIEventTarget> ref = new EventTargetWrapper(this);
return ref.forget();
}
nsresult
TaskQueue::Runner::Run()
{
RefPtr<nsIRunnable> event;
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
MOZ_ASSERT(mQueue->mIsRunning);
if (mQueue->mTasks.size() == 0) {
mQueue->mIsRunning = false;
mQueue->MaybeResolveShutdown();
mon.NotifyAll();
return NS_OK;
}
event = mQueue->mTasks.front().forget();
mQueue->mTasks.pop();
}
MOZ_ASSERT(event);
// Note that dropping the queue monitor before running the task, and
// taking the monitor again after the task has run ensures we have memory
// fences enforced. This means that if the object we're calling wasn't
// designed to be threadsafe, it will be, provided we're only calling it
// in this task queue.
{
AutoTaskGuard g(mQueue);
event->Run();
}
// Drop the reference to event. The event will hold a reference to the
// object it's calling, and we don't want to keep it alive, it may be
// making assumptions what holds references to it. This is especially
// the case if the object is waiting for us to shutdown, so that it
// can shutdown (like in the MediaDecoderStateMachine's SHUTDOWN case).
event = nullptr;
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
if (mQueue->mTasks.size() == 0) {
// No more events to run. Exit the task runner.
mQueue->mIsRunning = false;
mQueue->MaybeResolveShutdown();
mon.NotifyAll();
return NS_OK;
}
}
// There's at least one more event that we can run. Dispatch this Runner
// to the target again to ensure it runs again. Note that we don't just
// run in a loop here so that we don't hog the target. This means we may
// run on another thread next time, but we rely on the memory fences from
// mQueueMonitor for thread safety of non-threadsafe tasks.
nsresult rv = mQueue->mTarget->Dispatch(this, NS_DISPATCH_AT_END);
if (NS_FAILED(rv)) {
// Failed to dispatch, shutdown!
MonitorAutoLock mon(mQueue->mQueueMonitor);
mQueue->mIsRunning = false;
mQueue->mIsShutdown = true;
mQueue->MaybeResolveShutdown();
mon.NotifyAll();
}
return NS_OK;
}
} // namespace mozilla