The Tor Browser: content/media/MediaTaskQueue.cpp@44a2da4a2ab2 (annotated)

content/media/MediaTaskQueue.cpp@44a2da4a2ab2 (annotated)

content/media/MediaTaskQueue.cpp

Fri, 16 Jan 2015 04:50:19 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 04:50:19 +0100
branch: TOR_BUG_9701
changeset 13: 44a2da4a2ab2
permissions: -rw-r--r--

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

 /* -*- 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

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content/media/MediaTaskQueue.cpp@44a2da4a2ab2 (annotated)

content/media/MediaTaskQueue.cpp