MediaPlayer(九)--reset()流程

小蚂蚁与大象

发布于 2020-04-21 11:40:42

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发布于 2020-04-21 11:40:42

文章被收录于专栏：构建FFmpeg Android播放器构建FFmpeg Android播放器

frameworks/base/media/java/android/media/MediaPlayer.java

    /**
     * Resets the MediaPlayer to its uninitialized state. After calling
     * this method, you will have to initialize it again by setting the
     * data source and calling prepare().
     */
    public void reset() {
        mSelectedSubtitleTrackIndex = -1;
        synchronized(mOpenSubtitleSources) {
            for (final InputStream is: mOpenSubtitleSources) {
                try {
                    is.close();
                } catch (IOException e) {
                }
            }
            mOpenSubtitleSources.clear();
        }
        if (mSubtitleController != null) {
            mSubtitleController.reset();
        }
        if (mTimeProvider != null) {
            mTimeProvider.close();
            mTimeProvider = null;
        }

        stayAwake(false);
        _reset();
        // make sure none of the listeners get called anymore
        if (mEventHandler != null) {
            mEventHandler.removeCallbacksAndMessages(null);
        }

        synchronized (mIndexTrackPairs) {
            mIndexTrackPairs.clear();
            mInbandTrackIndices.clear();
        };

        resetDrmState();
    }

    private native void _reset();

主要步骤

销毁 Subtitle相关处理
销毁 mTimeProvider
stayAwake(false)，不保持屏幕长开的的状态
_reset()，调用到jni层，下面分析
销毁 mEventHandler所有消息，不再向播放器应用发送任何消息

frameworks/base/media/jni/android_media_MediaPlayer.cpp

static void
android_media_MediaPlayer_reset(JNIEnv *env, jobject thiz)
{
    ALOGV("reset");
    sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
    if (mp == NULL ) {
        jniThrowException(env, "java/lang/IllegalStateException", NULL);
        return;
    }
    process_media_player_call( env, thiz, mp->reset(), NULL, NULL );
}

frameworks/av/media/libmedia/mediaplayer.cpp

status_t MediaPlayer::reset_l()
{
    mLoop = false;
    if (mCurrentState == MEDIA_PLAYER_IDLE) return NO_ERROR;
    mPrepareSync = false;
    if (mPlayer != 0) {
        status_t ret = mPlayer->reset();
        if (ret != NO_ERROR) {
            ALOGE("reset() failed with return code (%d)", ret);
            mCurrentState = MEDIA_PLAYER_STATE_ERROR;
        } else {
            mPlayer->disconnect();
            mCurrentState = MEDIA_PLAYER_IDLE;
        }
        // setDataSource has to be called again to create a
        // new mediaplayer.
        mPlayer = 0;
        mCurrentBufferingSettings = BufferingSettings();
        return ret;
    }
    clear_l();
    return NO_ERROR;
}

主要步骤：

调用MediaPlayerService 的reset方法这一步主要执行到NuPlayer的reset
调用MediaPlayerService 的disconnect 这一步会销毁MediaPlayerService 保存的服务端mediaplayer binder实例mClient 和NuPlayer的实例
将mPlayer销毁 mPlayer是mediaplayer 同服务端MediaPlayerService

frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp

status_t MediaPlayerService::Client::reset()
{
    ALOGV("[%d] reset", mConnId);
    mMaybeVideoAlive = false;
    mRetransmitEndpointValid = false;
    sp<MediaPlayerBase> p = getPlayer();
    if (p == 0) return UNKNOWN_ERROR;
    return p->reset();
}

void MediaPlayerService::Client::disconnect()
{
    ALOGV("disconnect(%d) from pid %d", mConnId, mPid);
    // grab local reference and clear main reference to prevent future
    // access to object
    sp<MediaPlayerBase> p;
    {
        Mutex::Autolock l(mLock);
       //使用了一个局部变量对mPlayer引用，即对底层播放器的引用。
       //会使强引用计数加1。在这个函数退出后，p的生命周期也结束，智能指针会自动销毁底层播放器实例
        p = mPlayer;

       //调用了智能指针的clear方法，将强引用计数减1，并m_ptr = 0 
       //mClient 为sp<IMediaPlayerClient>，即是对mediaplayer的引用
       //mPlayer 为sp<MediaPlayerBase>
       //mClient和mPlayer为全局的引用变量，使用clear后， mClient和mPlayer将无法再被使用
        mClient.clear();      
        mPlayer.clear();
    }

    // clear the notification to prevent callbacks to dead client
    // and reset the player. We assume the player will serialize
    // access to itself if necessary.
    if (p != 0) {
        p->setNotifyCallback(0, 0);
#if CALLBACK_ANTAGONIZER
        ALOGD("kill Antagonizer");
        mAntagonizer->kill();
#endif
        p->reset();
    }

    {
        Mutex::Autolock l(mLock);
        disconnectNativeWindow_l();
    }

    IPCThreadState::self()->flushCommands();
}

disconnect步骤稍微有点绕。先用一个局部变量p 指向了mPlayer，即增加了对NuPlayer的强引用计数，接着销毁了全局变量mClient和mPlayer引用。mClient计数应该会为0，所以对应的实例也会被销毁。而NuPlayer的引用计数由于局部变量p，引用计数不会为0。接着通过p 将NuPlayer的回调函数置为0，并调用到NuPlayer的reset方法，这里是重复调用了reset方法，因为release流程只会调用mediaplayer的disconnect方法，不会调用到reset方法。在函数执行完后，局部变量p会自动销毁，同时也会自动销毁NuPlayer实例主要步骤：