Android Audio代码分析15 - testPlaybackHeadPositionAfterFlush

继续啃AudioTrack的测试代码。

*****************************************源码*************************************************
//Test case 2: getPlaybackHeadPosition() increases after play()
    @LargeTest
    public void testPlaybackHeadPositionIncrease() throws Exception {
        // constants for test
        final String TEST_NAME = "testPlaybackHeadPositionIncrease";
        final int TEST_SR = 22050;
        final int TEST_CONF = AudioFormat.CHANNEL_OUT_STEREO;
        final int TEST_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
        final int TEST_MODE = AudioTrack.MODE_STREAM;
        final int TEST_STREAM_TYPE = AudioManager.STREAM_MUSIC;

        //-------- initialization --------------
        int minBuffSize = AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT);
        AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,
                minBuffSize, TEST_MODE);
        byte data[] = new byte[minBuffSize/2];
        //--------    test        --------------
        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);
        track.write(data, 0, data.length);
        track.write(data, 0, data.length);
        track.play();
        Thread.sleep(100);
        log(TEST_NAME, "position ="+ track.getPlaybackHeadPosition());
        assertTrue(TEST_NAME, track.getPlaybackHeadPosition() > 0);
        //-------- tear down      --------------
        track.release();
    }
**********************************************************************************************
源码路径：
frameworks\base\media\tests\mediaframeworktest\src\com\android\mediaframeworktest\functional\MediaAudioTrackTest.java

#######################说明################################
//Test case 2: getPlaybackHeadPosition() increases after play()
// 在上一篇关于getPlaybackHeadPosition的分析中，没有调用play函数，就调用了getPlaybackHeadPosition，所以获取的position应该为0.
// 而本例子中，在write之后就调用了play，然后sleep了100ms，才调用的getPlaybackHeadPosition。
// 也就是说，播放了100ms才去获取的位置，此时的位置当然应该大于0
    @LargeTest
    public void testPlaybackHeadPositionIncrease() throws Exception {
        // constants for test
        final String TEST_NAME = "testPlaybackHeadPositionIncrease";
        final int TEST_SR = 22050;
        final int TEST_CONF = AudioFormat.CHANNEL_OUT_STEREO;
        final int TEST_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
        final int TEST_MODE = AudioTrack.MODE_STREAM;
        final int TEST_STREAM_TYPE = AudioManager.STREAM_MUSIC;

        //-------- initialization --------------
        int minBuffSize = AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT);
        AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,
                minBuffSize, TEST_MODE);
        byte data[] = new byte[minBuffSize/2];
        //--------    test        --------------
        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);
        track.write(data, 0, data.length);
        track.write(data, 0, data.length);
// 这次的引子是position如何被改变的
// 既然播放之后，获取的position为正，那么play函数的调用就应该会导致position的改变。
// 一起来看看play函数如何导致position改变的。
        track.play();
++++++++++++++++++++++++++++++play++++++++++++++++++++++++++++++++++
    /**
     * Starts playing an AudioTrack.
     * @throws IllegalStateException
     */
    public void play()
    throws IllegalStateException {
        if (mState != STATE_INITIALIZED) {
            throw(new IllegalStateException("play() called on uninitialized AudioTrack."));
        }

        synchronized(mPlayStateLock) {
            native_start();
++++++++++++++++++++++++++++++android_media_AudioTrack_start++++++++++++++++++++++++++++++++++
static void
android_media_AudioTrack_start(JNIEnv *env, jobject thiz)
{
    AudioTrack *lpTrack = (AudioTrack *)env->GetIntField(
        thiz, javaAudioTrackFields.nativeTrackInJavaObj);
    if (lpTrack == NULL ) {
        jniThrowException(env, "java/lang/IllegalStateException",
            "Unable to retrieve AudioTrack pointer for start()");
        return;
    }

    lpTrack->start();
++++++++++++++++++++++++++++++AudioTrack::start++++++++++++++++++++++++++++++++++
void AudioTrack::start()
{
// mAudioTrackThread在函数AudioTrack::set中被赋值。
    sp<AudioTrackThread> t = mAudioTrackThread;
    status_t status;

    LOGV("start %p", this);
    if (t != 0) {
// 函数exitPending返回成员变量mExitPending
        if (t->exitPending()) {
            if (t->requestExitAndWait() == WOULD_BLOCK) {
                LOGE("AudioTrack::start called from thread");

补充：移动开发 , Android ,