Android(安卓)Audio代码分析13 - AudioTrack::getPosition函数 - android

打算以测试代码中所使用的接口为点，以接口间调用关系为线，逐步撕开Android中Audio的面纱。

*****************************************源码*************************************************

    public void testPlaybackHeadPositionAfterInit() throws Exception {        // constants for test        final String TEST_NAME = "testPlaybackHeadPositionAfterInit";        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 --------------        AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,                 AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT), TEST_MODE);        //--------    test        --------------        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);        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 1: getPlaybackHeadPosition() at 0 after initialization    public void testPlaybackHeadPositionAfterInit() throws Exception {        // constants for test        final String TEST_NAME = "testPlaybackHeadPositionAfterInit";        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 --------------        AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,                 AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT), TEST_MODE);        //--------    test        --------------        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);// 今天要看的，就是下面的getPlaybackHeadPosition函数// 由于在getPlaybackHeadPosition之前，并没有调用play函数，也就是没有开始播放，所以获取的position应该为0        assertTrue(TEST_NAME, track.getPlaybackHeadPosition() == 0);// +++++++++++++++++++++++++++++++getPlaybackHeadPosition+++++++++++++++++++++++++++++++++    /**     * Returns the playback head position expressed in frames     */    public int getPlaybackHeadPosition() {// 很直接// 调用的是函数android_media_AudioTrack_get_position        return native_get_position();// ++++++++++++++++++++++++++++++android_media_AudioTrack_get_position++++++++++++++++++++++++++++++++++// 路径：frameworks\base\core\jni\android_media_AudioTrack.cppstatic jint android_media_AudioTrack_get_position(JNIEnv *env,  jobject thiz) {        AudioTrack *lpTrack = (AudioTrack *)env->GetIntField(                thiz, javaAudioTrackFields.nativeTrackInJavaObj);    uint32_t position = 0;                    if (lpTrack) {        lpTrack->getPosition(&position);        return (jint)position;// ++++++++++++++++++++++++++++++++AudioTrack::getPosition++++++++++++++++++++++++++++++++status_t AudioTrack::getPosition(uint32_t *position){    if (position == 0) return BAD_VALUE;    *position = mCblk->server;    return NO_ERROR;}// server是mCblk的成员变量，mCblk是audio_track_cblk_t对象。// server在函数audio_track_cblk_t::stepServer中有被赋值。// 另外，mCblk->server有在函数AudioTrack::setPosition中被赋值。// +++++++++++++++++++++++++++++++++AudioTrack::setPosition+++++++++++++++++++++++++++++++status_t AudioTrack::setPosition(uint32_t position){    Mutex::Autolock _l(mCblk->lock);    if (!stopped()) return INVALID_OPERATION;    if (position > mCblk->user) return BAD_VALUE;    mCblk->server = position;    mCblk->flags |= CBLK_FORCEREADY_ON;    return NO_ERROR;}// android_media_AudioTrack.cpp文件中的以下两个函数调用了AudioTrack::setPosition：// android_media_AudioTrack_set_pos_update_period函数// android_media_AudioTrack_set_position函数// 这些接口上给java层用的。// 想象一下使用场景，拖动当前光标？// ---------------------------------AudioTrack::setPosition-------------------------------// +++++++++++++++++++++++++++++++++audio_track_cblk_t::stepServer+++++++++++++++++++++++++++++++bool audio_track_cblk_t::stepServer(uint32_t frameCount){    // the code below simulates lock-with-timeout    // we MUST do this to protect the AudioFlinger server    // as this lock is shared with the client.    status_t err;    err = lock.tryLock();    if (err == -EBUSY) { // just wait a bit        usleep(1000);        err = lock.tryLock();    }    if (err != NO_ERROR) {        // probably, the client just died.        return false;    }    uint64_t s = this->server;    s += frameCount;    if (flags & CBLK_DIRECTION_MSK) {        // Mark that we have read the first buffer so that next time stepUser() is called        // we switch to normal obtainBuffer() timeout period        if (bufferTimeoutMs == MAX_STARTUP_TIMEOUT_MS) {            bufferTimeoutMs = MAX_STARTUP_TIMEOUT_MS - 1;        }        // It is possible that we receive a flush()        // while the mixer is processing a block: in this case,        // stepServer() is called After the flush() has reset u & s and        // we have s > u        if (s > this->user) {            LOGW("stepServer occured after track reset");            s = this->user;        }    }    if (s >= loopEnd) {        LOGW_IF(s > loopEnd, "stepServer: s %llu > loopEnd %llu", s, loopEnd);        s = loopStart;        if (--loopCount == 0) {            loopEnd = ULLONG_MAX;            loopStart = ULLONG_MAX;        }    }    if (s >= serverBase + this->frameCount) {        serverBase += this->frameCount;    }    this->server = s;    cv.signal();    lock.unlock();    return true;}// 函数AudioFlinger::ThreadBase::TrackBase::step中调用了函数audio_track_cblk_t::stepServer。// ++++++++++++++++++++++++++++++AudioFlinger::ThreadBase::TrackBase::step++++++++++++++++++++++++++++++++++bool AudioFlinger::ThreadBase::TrackBase::step() {    bool result;    audio_track_cblk_t* cblk = this->cblk();    result = cblk->stepServer(mFrameCount);    if (!result) {        LOGV("stepServer failed acquiring cblk mutex");        mFlags |= STEPSERVER_FAILED;    }    return result;}// 函数AudioFlinger::PlaybackThread::Track::getNextBuffer和函数AudioFlinger::RecordThread::RecordTrack::getNextBuffer// 调用了函数AudioFlinger::ThreadBase::TrackBase::step。// 我们这儿只看函数AudioFlinger::PlaybackThread::Track::getNextBuffer。// +++++++++++++++++++++++++++++AudioFlinger::PlaybackThread::Track::getNextBuffer+++++++++++++++++++++++++++++++++++status_t AudioFlinger::PlaybackThread::Track::getNextBuffer(AudioBufferProvider::Buffer* buffer){     audio_track_cblk_t* cblk = this->cblk();     uint32_t framesReady;     uint32_t framesReq = buffer->frameCount;     // Check if last stepServer failed, try to step now     if (mFlags & TrackBase::STEPSERVER_FAILED) {         if (!step())  goto getNextBuffer_exit;         LOGV("stepServer recovered");         mFlags &= ~TrackBase::STEPSERVER_FAILED;     }     framesReady = cblk->framesReady();     if (LIKELY(framesReady)) {        uint64_t s = cblk->server;        uint64_t bufferEnd = cblk->serverBase + cblk->frameCount;        bufferEnd = (cblk->loopEnd < bufferEnd) ? cblk->loopEnd : bufferEnd;        if (framesReq > framesReady) {            framesReq = framesReady;        }        if (s + framesReq > bufferEnd) {            framesReq = bufferEnd - s;        }         buffer->raw = getBuffer(s, framesReq);         if (buffer->raw == 0) goto getNextBuffer_exit;         buffer->frameCount = framesReq;        return NO_ERROR;     }getNextBuffer_exit:     buffer->raw = 0;     buffer->frameCount = 0;     LOGV("getNextBuffer() no more data for track %d on thread %p", mName, mThread.unsafe_get());     return NOT_ENOUGH_DATA;}// 该函数在看framesReady的时候已经看过了，此时就不再多说了。// -----------------------------AudioFlinger::PlaybackThread::Track::getNextBuffer-----------------------------------// ------------------------------AudioFlinger::ThreadBase::TrackBase::step----------------------------------// ---------------------------------audio_track_cblk_t::stepServer-------------------------------// --------------------------------AudioTrack::getPosition--------------------------------    }  else {        jniThrowException(env, "java/lang/IllegalStateException",            "Unable to retrieve AudioTrack pointer for getPosition()");        return AUDIOTRACK_ERROR;    }}// ------------------------------android_media_AudioTrack_get_position----------------------------------    }// -------------------------------getPlaybackHeadPosition---------------------------------        //-------- tear down      --------------        track.release();    }

###########################################################

&&&&&&&&&&&&&&&&&&&&&&&总结&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
get position其实就是取得audio_track_cblk_t对象中server的位置。
server的位置在set position或者step server的时候会被改变。
应用程序会set position。
Get next buffer的时候会step server。
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

Android(安卓)Audio代码分析13 - AudioTrack::getPosition函数

更多相关文章

随机推荐