gecko-dev/content/media/MediaTaskQueue.cpp

172 строки
4.4 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 "MediaTaskQueue.h"
#include "nsThreadUtils.h"
#include "SharedThreadPool.h"
namespace mozilla {
MediaTaskQueue::MediaTaskQueue(TemporaryRef<SharedThreadPool> aPool)
: mPool(aPool)
, mQueueMonitor("MediaTaskQueue::Queue")
, mIsRunning(false)
, mIsShutdown(false)
{
MOZ_COUNT_CTOR(MediaTaskQueue);
}
MediaTaskQueue::~MediaTaskQueue()
{
MonitorAutoLock mon(mQueueMonitor);
MOZ_ASSERT(mIsShutdown);
MOZ_COUNT_DTOR(MediaTaskQueue);
}
nsresult
MediaTaskQueue::Dispatch(TemporaryRef<nsIRunnable> aRunnable)
{
MonitorAutoLock mon(mQueueMonitor);
if (mIsShutdown) {
return NS_ERROR_FAILURE;
}
mTasks.push(aRunnable);
if (mIsRunning) {
return NS_OK;
}
RefPtr<nsIRunnable> runner(new Runner(this));
nsresult rv = mPool->Dispatch(runner, NS_DISPATCH_NORMAL);
if (NS_FAILED(rv)) {
NS_WARNING("Failed to dispatch runnable to run MediaTaskQueue");
return rv;
}
mIsRunning = true;
return NS_OK;
}
void
MediaTaskQueue::AwaitIdle()
{
MonitorAutoLock mon(mQueueMonitor);
AwaitIdleLocked();
}
void
MediaTaskQueue::AwaitIdleLocked()
{
mQueueMonitor.AssertCurrentThreadOwns();
MOZ_ASSERT(mIsRunning || mTasks.empty());
while (mIsRunning) {
mQueueMonitor.Wait();
}
}
void
MediaTaskQueue::Shutdown()
{
MonitorAutoLock mon(mQueueMonitor);
mIsShutdown = true;
AwaitIdleLocked();
}
void
MediaTaskQueue::Flush()
{
MonitorAutoLock mon(mQueueMonitor);
while (!mTasks.empty()) {
mTasks.pop();
}
AwaitIdleLocked();
}
bool
MediaTaskQueue::IsEmpty()
{
MonitorAutoLock mon(mQueueMonitor);
return mTasks.empty();
}
bool
MediaTaskQueue::IsCurrentThreadIn()
{
#ifdef DEBUG
MonitorAutoLock mon(mQueueMonitor);
return NS_GetCurrentThread() == mRunningThread;
#else
return false;
#endif
}
nsresult
MediaTaskQueue::Runner::Run()
{
RefPtr<nsIRunnable> event;
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
MOZ_ASSERT(mQueue->mIsRunning);
mQueue->mRunningThread = NS_GetCurrentThread();
if (mQueue->mTasks.size() == 0) {
mQueue->mIsRunning = false;
mon.NotifyAll();
return NS_OK;
}
event = mQueue->mTasks.front();
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.
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;
mon.NotifyAll();
mQueue->mRunningThread = nullptr;
return NS_OK;
}
}
// There's at least one more event that we can run. Dispatch this Runner
// to the thread pool again to ensure it runs again. Note that we don't just
// run in a loop here so that we don't hog the thread pool. 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.
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
// Note: Hold the monitor *before* we dispatch, in case we context switch
// to another thread pool in the queue immediately and take the lock in the
// other thread; mRunningThread could be set to the new thread's value and
// then incorrectly anulled below in that case.
nsresult rv = mQueue->mPool->Dispatch(this, NS_DISPATCH_NORMAL);
if (NS_FAILED(rv)) {
// Failed to dispatch, shutdown!
mQueue->mIsRunning = false;
mQueue->mIsShutdown = true;
mon.NotifyAll();
}
mQueue->mRunningThread = nullptr;
}
return NS_OK;
}
} // namespace mozilla