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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "media/audio/scoped_task_runner_observer.h"
      6 
      7 #include "base/bind.h"
      8 #include "base/synchronization/waitable_event.h"
      9 
     10 namespace media {
     11 
     12 ScopedTaskRunnerObserver::ScopedTaskRunnerObserver(
     13     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
     14     : task_runner_(task_runner) {
     15   ObserveLoopDestruction(true, NULL);
     16 }
     17 
     18 ScopedTaskRunnerObserver::~ScopedTaskRunnerObserver() {
     19   ObserveLoopDestruction(false, NULL);
     20 }
     21 
     22 void ScopedTaskRunnerObserver::ObserveLoopDestruction(
     23     bool enable,
     24     base::WaitableEvent* done) {
     25   // Note: |done| may be NULL.
     26   if (task_runner_->BelongsToCurrentThread()) {
     27     base::MessageLoop* loop = base::MessageLoop::current();
     28     if (enable) {
     29       loop->AddDestructionObserver(this);
     30     } else {
     31       loop->RemoveDestructionObserver(this);
     32     }
     33   } else {
     34     base::WaitableEvent event(false, false);
     35     if (task_runner_->PostTask(FROM_HERE,
     36             base::Bind(&ScopedTaskRunnerObserver::ObserveLoopDestruction,
     37                        base::Unretained(this), enable, &event))) {
     38       event.Wait();
     39     } else {
     40       // The message loop's thread has already terminated, so no need to wait.
     41     }
     42   }
     43 
     44   if (done)
     45     done->Signal();
     46 }
     47 
     48 }  // namespace media.
     49