Audio笔记之PlaybackThread::threadLoop

bool AudioFlinger::PlaybackThread::threadLoop()
{
    Vector< sp<Track> > tracksToRemove;

    standbyTime = systemTime();

    // MIXER
    nsecs_t lastWarning = 0;

    // DUPLICATING
    // FIXME could this be made local to while loop?
    writeFrames = 0;

    int lastGeneration = 0;

    cacheParameters_l();
    sleepTime = idleSleepTime;

    if (mType == MIXER) {
        sleepTimeShift = 0;
    }

    CpuStats cpuStats;
    const String8 myName(String8::format("thread %p type %d TID %d", this, mType, gettid()));

    acquireWakeLock();

    // mNBLogWriter->log can only be called while thread mutex mLock is held.
    // So if you need to log when mutex is unlocked, set logString to a non-NULL string,
    // and then that string will be logged at the next convenient opportunity.
    const char *logString = NULL;

    checkSilentMode_l();

    while (!exitPending())
    {
        cpuStats.sample(myName);

        Vector< sp<EffectChain> > effectChains;

        processConfigEvents();

        { // scope for mLock

            Mutex::Autolock _l(mLock);

            if (logString != NULL) {
                mNBLogWriter->logTimestamp();
                mNBLogWriter->log(logString);
                logString = NULL;
            }

            if (mLatchDValid) {
                mLatchQ = mLatchD;
                mLatchDValid = false;
                mLatchQValid = true;
            }
            //检查客户端设置的更新，客户端通过setParameters进行设置
            if (checkForNewParameters_l()) {
                cacheParameters_l();
            }

            saveOutputTracks();
            //判断是否有track加入
            if (mSignalPending) {
                // A signal was raised while we were unlocked
                mSignalPending = false;
            } else if (waitingAsyncCallback_l()) {//offload时返回true
                if (exitPending()) {
                    break;
                }
                releaseWakeLock_l();
                mWakeLockUids.clear();
                mActiveTracksGeneration++;
                ALOGV("wait async completion");
                mWaitWorkCV.wait(mLock);
                ALOGV("async completion/wake");
                acquireWakeLock_l();
                standbyTime = systemTime() + standbyDelay;
                sleepTime = 0;

                continue;
            }
            //两种情况需要硬件进入standby  
            //第一:没有活跃音轨而且standbyTime过期  
            //第二:需要Suspend  
            if ((!mActiveTracks.size() && systemTime() > standbyTime) ||
                                   isSuspended()) {
                // put audio hardware into standby after short delay
                if (shouldStandby_l()) {

                    threadLoop_standby();

                    mStandby = true;
                }
                //如果当前config event也为空，则进入阻塞状态
                if (!mActiveTracks.size() && mConfigEvents.isEmpty()) {
                    // we're about to wait, flush the binder command buffer
                    IPCThreadState::self()->flushCommands();

                    clearOutputTracks();

                    if (exitPending()) {
                        break;
                    }

                    releaseWakeLock_l();
                    mWakeLockUids.clear();
                    mActiveTracksGeneration++;

                    // wait until we have something to do...
                    // 当前没有可供使用的active track，进程进入阻塞状态，
                    // 等待广播消息唤醒，包括配置参数、活跃音轨添加等消息
                    ALOGV("%s going to sleep", myName.string());
                    mWaitWorkCV.wait(mLock);
                    ALOGV("%s waking up", myName.string());
                    acquireWakeLock_l();

                    mMixerStatus = MIXER_IDLE;
                    mMixerStatusIgnoringFastTracks = MIXER_IDLE;
                    mBytesWritten = 0;
                    mBytesRemaining = 0;
                    checkSilentMode_l();

                    standbyTime = systemTime() + standbyDelay;
                    sleepTime = idleSleepTime;
                    if (mType == MIXER) {
                        sleepTimeShift = 0;
                    }

                    continue;
                }
            }
            // mMixerStatusIgnoringFastTracks is also updated internally
            // 准备音轨，为混音做准备
            mMixerStatus = prepareTracks_l(&tracksToRemove);

            // compare with previously applied list
            if (lastGeneration != mActiveTracksGeneration) {
                // update wakelock
                updateWakeLockUids_l(mWakeLockUids);
                lastGeneration = mActiveTracksGeneration;
            }

            // prevent any changes in effect chain list and in each effect chain
            // during mixing and effect process as the audio buffers could be deleted
            // or modified if an effect is created or deleted
            lockEffectChains_l(effectChains);
        } // mLock scope ends
        //混音处理后数据全部写入Hal之后，会将mBytesRemaining置为0
        //即表示当前可以进行新一轮的Mix操作
        if (mBytesRemaining == 0) {
            mCurrentWriteLength = 0;
            if (mMixerStatus == MIXER_TRACKS_READY) {
                // threadLoop_mix() sets mCurrentWriteLength
                threadLoop_mix();
            } else if ((mMixerStatus != MIXER_DRAIN_TRACK)
                        && (mMixerStatus != MIXER_DRAIN_ALL)) {
                // threadLoop_sleepTime sets sleepTime to 0 if data
                // must be written to HAL
                threadLoop_sleepTime();
                if (sleepTime == 0) {
                    mCurrentWriteLength = mixBufferSize;
                }
            }
            mBytesRemaining = mCurrentWriteLength;
            if (isSuspended()) {
                sleepTime = suspendSleepTimeUs();
                // simulate write to HAL when suspended
                mBytesWritten += mixBufferSize;
                mBytesRemaining = 0;
            }

            // only process effects if we're going to write
            // 进行音效处理，同时避免offload类型的输出重复处理
            if (sleepTime == 0 && mType != OFFLOAD) {
                for (size_t i = 0; i < effectChains.size(); i ++) {
                    effectChains[i]->process_l();
                }
            }
        }
        // Process effect chains for offloaded thread even if no audio
        // was read from audio track: process only updates effect state
        // and thus does have to be synchronized with audio writes but may have
        // to be called while waiting for async write callback
        // 当输出线程为offload类型时，即使没有读取track数据，
        // 也需要对effect chain进行处理，更新effect状态
        if (mType == OFFLOAD) {
            for (size_t i = 0; i < effectChains.size(); i ++) {
                effectChains[i]->process_l();
            }
        }

        // enable changes in effect chain
        unlockEffectChains(effectChains);
        //需要对OffloadThread类型的输出进行条件判断，
        //其它情况为true
        if (!waitingAsyncCallback()) {
            // sleepTime == 0 means we must write to audio hardware
            //1、休眠时间为0，且MIX处理之后的数据不会空时，将数据写入到Hal，
            //   返回写入的数据量，如果小于零，则直接将mBytesRemaining置0
            //   其它情况则增加已写入数据量，减少Mix已处理量
            if (sleepTime == 0) {
                if (mBytesRemaining) {
                    ssize_t ret = threadLoop_write();
                    if (ret < 0) {
                        mBytesRemaining = 0;
                    } else {
                        mBytesWritten += ret;
                        mBytesRemaining -= ret;
                    }
                } else if ((mMixerStatus == MIXER_DRAIN_TRACK) ||
                        (mMixerStatus == MIXER_DRAIN_ALL)) {
                    threadLoop_drain();
                }
                //如果该线程为混音线程，总共有五类线程，计算该线程上一次写入和
                //和本次写入的时间差，如果大于最多允许的延迟时间，则增加延迟的计数，
                //并发出警告，属于underrun
    /*
    enum type_t {
        MIXER,              // Thread class is MixerThread
        DIRECT,             // Thread class is DirectOutputThread
        DUPLICATING,        // Thread class is DuplicatingThread
        RECORD,             // Thread class is RecordThread
        OFFLOAD             // Thread class is OffloadThread
    };
     */
                if (mType == MIXER) {
                    // write blocked detection
                    nsecs_t now = systemTime();
                    nsecs_t delta = now - mLastWriteTime;
                    if (!mStandby && delta > maxPeriod) {
                        mNumDelayedWrites++;
                        if ((now - lastWarning) > kWarningThrottleNs) {
                            ATRACE_NAME("underrun");
                            ALOGW("write blocked for %llu msecs, %d delayed writes, thread %p",
                                ns2ms(delta), mNumDelayedWrites, this);
                            lastWarning = now;
                        }
                    }
               }

            } else {
                usleep(sleepTime);
            }
        }

        // Finally let go of removed track(s), without the lock held
        // since we can't guarantee the destructors won't acquire that
        // same lock.  This will also mutate and push a new fast mixer state.
        threadLoop_removeTracks(tracksToRemove);
        tracksToRemove.clear();

        // FIXME I don't understand the need for this here;
        //       it was in the original code but maybe the
        //       assignment in saveOutputTracks() makes this unnecessary?
        clearOutputTracks();

        // Effect chains will be actually deleted here if they were removed from
        // mEffectChains list during mixing or effects processing
        effectChains.clear();

        // FIXME Note that the above .clear() is no longer necessary since effectChains
        // is now local to this block, but will keep it for now (at least until merge done).
    }

    threadLoop_exit();

    // for DuplicatingThread, standby mode is handled by the outputTracks, otherwise ...
    if (mType == MIXER || mType == DIRECT || mType == OFFLOAD) {
        // put output stream into standby mode
        if (!mStandby) {
            mOutput->stream->common.standby(&mOutput->stream->common);
        }
    }

    releaseWakeLock();
    mWakeLockUids.clear();
    mActiveTracksGeneration++;

    ALOGV("Thread %p type %d exiting", this, mType);
    return false;
}

void AudioFlinger::ThreadBase::processConfigEvents()
{
    mLock.lock();
    while (!mConfigEvents.isEmpty()) {
        ALOGV("processConfigEvents() remaining events %d", mConfigEvents.size());
        ConfigEvent *event = mConfigEvents[0];
        mConfigEvents.removeAt(0);
        // release mLock before locking AudioFlinger mLock: lock order is always
        // AudioFlinger then ThreadBase to avoid cross deadlock
        mLock.unlock();
        switch(event->type()) {
            case CFG_EVENT_PRIO: {
                PrioConfigEvent *prioEvent = static_cast<PrioConfigEvent *>(event);
                // FIXME Need to understand why this has be done asynchronously
                int err = requestPriority(prioEvent->pid(), prioEvent->tid(), prioEvent->prio(),
                        true /*asynchronous*/);
                if (err != 0) {
                    ALOGW("Policy SCHED_FIFO priority %d is unavailable for pid %d tid %d; "
                          "error %d",
                          prioEvent->prio(), prioEvent->pid(), prioEvent->tid(), err);
                }
            } break;
            case CFG_EVENT_IO: {
                IoConfigEvent *ioEvent = static_cast<IoConfigEvent *>(event);
                mAudioFlinger->mLock.lock();
                audioConfigChanged_l(ioEvent->event(), ioEvent->param());
                mAudioFlinger->mLock.unlock();
            } break;
            default:
                ALOGE("processConfigEvents() unknown event type %d", event->type());
                break;
        }
        delete event;
        mLock.lock();
    }
    mLock.unlock();
}

// Parameter sequence by client: binder thread calling setParameters():
//  1. Lock mLock
//  2. Append to mNewParameters
//  3. mWaitWorkCV.signal
//  4. mParamCond.waitRelative with timeout
//  5. read mParamStatus
//  6. mWaitWorkCV.signal
//  7. Unlock
status_t AudioFlinger::ThreadBase::setParameters(const String8& keyValuePairs)
{
    status_t status;

    ALOGV("ThreadBase::setParameters() %s", keyValuePairs.string());
    Mutex::Autolock _l(mLock);

    mNewParameters.add(keyValuePairs);
    mWaitWorkCV.signal();//唤醒loop线程，设置parameters
    // wait condition with timeout in case the thread loop has exited
    // before the request could be processed
    // 休眠等待，之后返回checkForNewParameters_l设置参数的状态mParamStatus
    if (mParamCond.waitRelative(mLock, kSetParametersTimeoutNs) == NO_ERROR) {
        status = mParamStatus;
        mWaitWorkCV.signal();//唤醒loop线程
    } else {
        status = TIMED_OUT;
    }
    return status;
}

// Parameter sequence by server: threadLoop calling checkForNewParameters_l():
// 1. Lock mLock
// 2. If there is an entry in mNewParameters proceed ...
// 2. Read first entry in mNewParameters
// 3. Process
// 4. Remove first entry from mNewParameters
// 5. Set mParamStatus
// 6. mParamCond.signal
// 7. mWaitWorkCV.wait with timeout (this is to avoid overwriting mParamStatus)
// 8. Unlock
bool AudioFlinger::MixerThread::checkForNewParameters_l()
{
    // if !&IDLE, holds the FastMixer state to restore after new parameters processed
    FastMixerState::Command previousCommand = FastMixerState::HOT_IDLE;
    bool reconfig = false;

    while (!mNewParameters.isEmpty()) {

        if (mFastMixer != NULL) {
            FastMixerStateQueue *sq = mFastMixer->sq();
            FastMixerState *state = sq->begin();
            if (!(state->mCommand & FastMixerState::IDLE)) {
                previousCommand = state->mCommand;
                state->mCommand = FastMixerState::HOT_IDLE;
                sq->end();
                sq->push(FastMixerStateQueue::BLOCK_UNTIL_ACKED);
            } else {
                sq->end(false /*didModify*/);
            }
        }

        status_t status = NO_ERROR;
        String8 keyValuePair = mNewParameters[0];
        AudioParameter param = AudioParameter(keyValuePair);
        int value;

        if (param.getInt(String8(AudioParameter::keySamplingRate), value) == NO_ERROR) {
            reconfig = true;
        }
        if (param.getInt(String8(AudioParameter::keyFormat), value) == NO_ERROR) {
            if ((audio_format_t) value != AUDIO_FORMAT_PCM_16_BIT) {
                status = BAD_VALUE;
            } else {
                reconfig = true;
            }
        }
        if (param.getInt(String8(AudioParameter::keyChannels), value) == NO_ERROR) {
            if ((audio_channel_mask_t) value != AUDIO_CHANNEL_OUT_STEREO) {
                status = BAD_VALUE;
            } else {
                reconfig = true;
            }
        }
        if (param.getInt(String8(AudioParameter::keyFrameCount), value) == NO_ERROR) {
            // do not accept frame count changes if tracks are open as the track buffer
            // size depends on frame count and correct behavior would not be guaranteed
            // if frame count is changed after track creation
            if (!mTracks.isEmpty()) {
                status = INVALID_OPERATION;
            } else {
                reconfig = true;
            }
        }
        if (param.getInt(String8(AudioParameter::keyRouting), value) == NO_ERROR) {
            // forward device change to effects that have requested to be
            // aware of attached audio device.
            if (value != AUDIO_DEVICE_NONE) {
                mOutDevice = value;
                for (size_t i = 0; i < mEffectChains.size(); i++) {
                    mEffectChains[i]->setDevice_l(mOutDevice);
                }
            }
        }

        if (status == NO_ERROR) {
            status = mOutput->stream->common.set_parameters(&mOutput->stream->common,
                                                    keyValuePair.string());
            if (!mStandby && status == INVALID_OPERATION) {
                mOutput->stream->common.standby(&mOutput->stream->common);
                mStandby = true;
                mBytesWritten = 0;
                status = mOutput->stream->common.set_parameters(&mOutput->stream->common,
                                                       keyValuePair.string());
            }
            if (status == NO_ERROR && reconfig) {
                readOutputParameters();
                delete mAudioMixer;
                mAudioMixer = new AudioMixer(mNormalFrameCount, mSampleRate);
                for (size_t i = 0; i < mTracks.size() ; i++) {
                    int name = getTrackName_l(mTracks[i]->mChannelMask, mTracks[i]->mSessionId);
                    if (name < 0) {
                        break;
                    }
                    mTracks[i]->mName = name;
                }
                sendIoConfigEvent_l(AudioSystem::OUTPUT_CONFIG_CHANGED);
            }
        }
        //移除此参数
        mNewParameters.removeAt(0);

        mParamStatus = status;
        mParamCond.signal();//唤醒track对象
        // wait for condition with time out in case the thread calling ThreadBase::setParameters()
        // already timed out waiting for the status and will never signal the condition.
        // 休眠等待track端处理
        mWaitWorkCV.waitRelative(mLock, kSetParametersTimeoutNs);
    }

    if (!(previousCommand & FastMixerState::IDLE)) {
        ALOG_ASSERT(mFastMixer != NULL);
        FastMixerStateQueue *sq = mFastMixer->sq();
        FastMixerState *state = sq->begin();
        ALOG_ASSERT(state->mCommand == FastMixerState::HOT_IDLE);
        state->mCommand = previousCommand;
        sq->end();
        sq->push(FastMixerStateQueue::BLOCK_UNTIL_PUSHED);
    }

    return reconfig;
}

void AudioFlinger::MixerThread::threadLoop_standby()
{
    // Idle the fast mixer if it's currently running
    if (mFastMixer != NULL) {
        FastMixerStateQueue *sq = mFastMixer->sq();
        FastMixerState *state = sq->begin();
        if (!(state->mCommand & FastMixerState::IDLE)) {
            state->mCommand = FastMixerState::COLD_IDLE;
            state->mColdFutexAddr = &mFastMixerFutex;
            state->mColdGen++;
            mFastMixerFutex = 0;
            sq->end();
            // BLOCK_UNTIL_PUSHED would be insufficient, as we need it to stop doing I/O now
            sq->push(FastMixerStateQueue::BLOCK_UNTIL_ACKED);
            if (kUseFastMixer == FastMixer_Dynamic) {
                mNormalSink = mOutputSink;
            }
#ifdef AUDIO_WATCHDOG
            if (mAudioWatchdog != 0) {
                mAudioWatchdog->pause();
            }
#endif
        } else {
            sq->end(false /*didModify*/);
        }
    }
    PlaybackThread::threadLoop_standby();
}

void AudioFlinger::PlaybackThread::threadLoop_standby()
{
    ALOGV("Audio hardware entering standby, mixer %p, suspend count %d", this, mSuspended);
    mOutput->stream->common.standby(&mOutput->stream->common);
    if (mUseAsyncWrite != 0) {
        // discard any pending drain or write ack by incrementing sequence
        mWriteAckSequence = (mWriteAckSequence + 2) & ~1;
        mDrainSequence = (mDrainSequence + 2) & ~1;
        ALOG_ASSERT(mCallbackThread != 0);
        mCallbackThread->setWriteBlocked(mWriteAckSequence);
        mCallbackThread->setDraining(mDrainSequence);
    }
}
void AudioFlinger::MixerThread::threadLoop_mix()
{
    // obtain the presentation timestamp of the next output buffer
    int64_t pts;
    status_t status = INVALID_OPERATION;

    if (mNormalSink != 0) {
        status = mNormalSink->getNextWriteTimestamp(&pts);
    } else {
        status = mOutputSink->getNextWriteTimestamp(&pts);
    }

    if (status != NO_ERROR) {
        pts = AudioBufferProvider::kInvalidPTS;
    }

    // mix buffers...
    mAudioMixer->process(pts);
    mCurrentWriteLength = mixBufferSize;
    // increase sleep time progressively when application underrun condition clears.
    // Only increase sleep time if the mixer is ready for two consecutive times to avoid
    // that a steady state of alternating ready/not ready conditions keeps the sleep time
    // such that we would underrun the audio HAL.
    if ((sleepTime == 0) && (sleepTimeShift > 0)) {
        sleepTimeShift--;
    }
    sleepTime = 0;
    standbyTime = systemTime() + standbyDelay;
    //TODO: delay standby when effects have a tail
}
void AudioFlinger::MixerThread::threadLoop_sleepTime()
{
    // If no tracks are ready, sleep once for the duration of an output
    // buffer size, then write 0s to the output
    if (sleepTime == 0) {
        if (mMixerStatus == MIXER_TRACKS_ENABLED) {
            sleepTime = activeSleepTime >> sleepTimeShift;
            if (sleepTime < kMinThreadSleepTimeUs) {
                sleepTime = kMinThreadSleepTimeUs;
            }
            // reduce sleep time in case of consecutive application underruns to avoid
            // starving the audio HAL. As activeSleepTimeUs() is larger than a buffer
            // duration we would end up writing less data than needed by the audio HAL if
            // the condition persists.
            if (sleepTimeShift < kMaxThreadSleepTimeShift) {
                sleepTimeShift++;
            }
        } else {
            sleepTime = idleSleepTime;
        }
    } else if (mBytesWritten != 0 || (mMixerStatus == MIXER_TRACKS_ENABLED)) {
        memset (mMixBuffer, 0, mixBufferSize);
        sleepTime = 0;
        ALOGV_IF(mBytesWritten == 0 && (mMixerStatus == MIXER_TRACKS_ENABLED),
                "anticipated start");
    }
    // TODO add standby time extension fct of effect tail
}

void AudioFlinger::PlaybackThread::threadLoop_drain()
{
    if (mOutput->stream->drain) {
        ALOGV("draining %s", (mMixerStatus == MIXER_DRAIN_TRACK) ? "early" : "full");
        if (mUseAsyncWrite) {
            ALOGW_IF(mDrainSequence & 1, "threadLoop_drain(): out of sequence drain request");
            mDrainSequence |= 1;
            ALOG_ASSERT(mCallbackThread != 0);
            mCallbackThread->setDraining(mDrainSequence);
        }
        mOutput->stream->drain(mOutput->stream,
            (mMixerStatus == MIXER_DRAIN_TRACK) ? AUDIO_DRAIN_EARLY_NOTIFY
                                                : AUDIO_DRAIN_ALL);
    }
}
void AudioFlinger::MixerThread::threadLoop_removeTracks(const Vector< sp<Track> >& tracksToRemove)
{
    PlaybackThread::threadLoop_removeTracks(tracksToRemove);
}
void AudioFlinger::PlaybackThread::threadLoop_removeTracks(
        const Vector< sp<Track> >& tracksToRemove)
{
    size_t count = tracksToRemove.size();
    if (count) {
        for (size_t i = 0 ; i < count ; i++) {
            const sp<Track>& track = tracksToRemove.itemAt(i);
            if (!track->isOutputTrack()) {
                AudioSystem::stopOutput(mId, track->streamType(), track->sessionId());
#ifdef ADD_BATTERY_DATA
                // to track the speaker usage
                addBatteryData(IMediaPlayerService::kBatteryDataAudioFlingerStop);
#endif
                if (track->isTerminated()) {
                    AudioSystem::releaseOutput(mId);
                }
            }
        }
    }
}