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https://developer.android.com/reference/android/media/AudioFocusRequest

这是 Android 开发人员关于 AudioFocusRequest 的文档的链接。以下是该文档中给出的代码示例中的一些代码片段。我怀疑为什么需要在这些代码行中使用同步块？我知道同步块的功能是什么。我想知道的是，如果在这种情况下该代码块不同步，可能会出现什么问题。

requestAudioFocus 的代码片段：

    int res = mAudioManager.requestAudioFocus(mFocusRequest);
 synchronized (mFocusLock) {
     if (res == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
         mPlaybackDelayed = false;
     } else if (res == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
         mPlaybackDelayed = false;
         playbackNow();
     } else if (res == AudioManager.AUDIOFOCUS_REQUEST_DELAYED) {
        mPlaybackDelayed = true;
     }
 }

OnFocusChangeListener 的代码片段：

@Override
 public void onAudioFocusChange(int focusChange) {
     switch (focusChange) {
         case AudioManager.AUDIOFOCUS_GAIN:
             if (mPlaybackDelayed || mResumeOnFocusGain) {
                 synchronized (mFocusLock) {
                     mPlaybackDelayed = false;
                     mResumeOnFocusGain = false;
                 }
                 playbackNow();
             }
             break;
         case AudioManager.AUDIOFOCUS_LOSS:
             synchronized (mFocusLock) {
                 // this is not a transient loss, we shouldn't automatically resume for now
                 mResumeOnFocusGain = false;
                 mPlaybackDelayed = false;
             }
             pausePlayback();
             break;
         case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
         case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
             // we handle all transient losses the same way because we never duck audio books
             synchronized (mFocusLock) {
                 // we should only resume if playback was interrupted
                 mResumeOnFocusGain = mMediaPlayer.isPlaying();
                 mPlaybackDelayed = false;
             }
             pausePlayback();
             break;
     }
 }

我希望我的疑问很清楚。提前致谢。

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