Android Audio代码分析27 - Strategy 优先级

status_t AudioFlinger::PlaybackThread::Track::start(){    status_t status = NO_ERROR;    LOGV("start(%d), calling thread %d session %d",            mName, IPCThreadState::self()->getCallingPid(), mSessionId);// mThread 在 AudioFlinger::ThreadBase::TrackBase 的构造函数中被赋值// 数值由 AudioFlinger::PlaybackThread::Track 传给其父类 ThreadBase// 函数 AudioFlinger::PlaybackThread::createTrack_l 创建了 AudioFlinger::PlaybackThread::Track 对象// 与 thread 对应的参数是自身的 this 指针// 函数 AudioFlinger::openOutput 中创建了类 PlaybackThread 的子类 MixerThread 的对象，// 并将其和一个 id 一同添加到 mPlaybackThreads 中。// 下面使用的 thread->id() 就是此处的 id 。// 不过，有一点困惑的是，下面使用 thread->id() 的时候，其实是把它作为一个 output 来使用的。// id 和 output 究竟是什么关系呢？// 在函数 AudioFlinger::openOutput 中找到了答案，调用函数 AudioFlinger::openOutput 来打开一个 output 时，得到的返回值其实是上面所说的 thread 的 id 。// AudioPolicyManagerBase 中会将该 id 和一个 AudioOutputDescriptor 对象作为一对保存在 mOutputs 中。    sp<ThreadBase> thread = mThread.promote();    if (thread != 0) {        Mutex::Autolock _l(thread->mLock);        int state = mState;        // here the track could be either new, or restarted        // in both cases "unstop" the track        if (mState == PAUSED) {            mState = TrackBase::RESUMING;            LOGV("PAUSED => RESUMING (%d) on thread %p", mName, this);        } else {            mState = TrackBase::ACTIVE;            LOGV("? => ACTIVE (%d) on thread %p", mName, this);        }        if (!isOutputTrack() && state != ACTIVE && state != RESUMING) {            thread->mLock.unlock();// 下面的 thread->id() 对应的是调用函数 AudioPolicyService::openOutput 得到的 output 。// 函数 AudioSystem::startOutput 的实现直接调用了函数 AudioPolicyService::startOutput // 函数 AudioPolicyService::startOutput 的实现就是调用函数 AudioPolicyManagerBase::startOutput            status = AudioSystem::startOutput(thread->id(),                                              (AudioSystem::stream_type)mStreamType,                                              mSessionId);            thread->mLock.lock();        }        if (status == NO_ERROR) {            PlaybackThread *playbackThread = (PlaybackThread *)thread.get();            playbackThread->addTrack_l(this);        } else {            mState = state;        }    } else {        status = BAD_VALUE;    }    return status;}status_t AudioPolicyManagerBase::startOutput(audio_io_handle_t output,                                             AudioSystem::stream_type stream,                                             int session){    LOGV("startOutput() output %d, stream %d, session %d", output, stream, session);    ssize_t index = mOutputs.indexOfKey(output);    if (index < 0) {        LOGW("startOutput() unknow output %d", output);        return BAD_VALUE;    }// 对象的由来：// 函数 AudioPolicyManagerBase::AudioPolicyManagerBase 中打开了 DEVICE_OUT_SPEAKER 对应的 output ，并将其赋值给 AudioPolicyManagerBase 的成员变量 mHardwareOutput 。// 然后为该 output 创建一个 AudioOutputDescriptor 对象 (outputDesc) ，然后将 mHardwareOutput 和 outputDesc 作为一对添加到 mOutputs 中。// 最后调用函数 setOutputDevice 将默认的 output device 设置为 DEVICE_OUT_SPEAKER ： setOutputDevice(mHardwareOutput, (uint32_t)AudioSystem::DEVICE_OUT_SPEAKER, true);// 函数 AudioPolicyManagerBase::getOutput 中，若是 open 了一个 output ，也会为其创建一个 AudioOutputDescriptor 对象，并将它们添加到 mOutputs 中。// 根据 output 找到其对应的 AudioOutputDescriptor 对象。// AudioOutputDescriptor 对象在 AudioPolicyManagerBase 的构造函数或函数 AudioPolicyManagerBase::getOutput 中被创建，并和 output 作为一对添加到 mOutputs 中。    AudioOutputDescriptor *outputDesc = mOutputs.valueAt(index);    routing_strategy strategy = getStrategy((AudioSystem::stream_type)stream);#ifdef WITH_A2DP    if (mA2dpOutput != 0  && !a2dpUsedForSonification() && strategy == STRATEGY_SONIFICATION) {        setStrategyMute(STRATEGY_MEDIA, true, mA2dpOutput);    }#endif    // incremenent usage count for this stream on the requested output:    // NOTE that the usage count is the same for duplicated output and hardware output which is    // necassary for a correct control of hardware output routing by startOutput() and stopOutput()// AudioOutputDescriptor 对象中有一个数组，保存了该 output 中每个 stream 的使用计数// 函数 getNewDevice 中会使用到该计数    outputDesc->changeRefCount(stream, 1);// getNewDevice 函数的实现请看下面的代码// setOutputDevice 函数的实现，后面也有分析    setOutputDevice(output, getNewDevice(output));    // handle special case for sonification while in call    if (isInCall()) {// 此处是对来电话时 sonification 策略的特殊处理。// 若 stream 是低可见的，则将该 stream mute 掉// 否则会 startTone        handleIncallSonification(stream, true, false);    }    // apply volume rules for current stream and device if necessary// checkAndSetVolume 函数的实现在后面有看    checkAndSetVolume(stream, mStreams[stream].mIndexCur, output, outputDesc->device());    return NO_ERROR;}// 为 output 查找一个 device 。// 函数中涉及到的 strategy 的优先级，是为该 output 寻找哪个 strategy 对应的 device 的优先级。uint32_t AudioPolicyManagerBase::getNewDevice(audio_io_handle_t output, bool fromCache){    uint32_t device = 0;    AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output);    // check the following by order of priority to request a routing change if necessary:    // 1: we are in call or the strategy phone is active on the hardware output:    //      use device for strategy phone    // 2: the strategy sonification is active on the hardware output:    //      use device for strategy sonification    // 3: the strategy media is active on the hardware output:    //      use device for strategy media    // 4: the strategy DTMF is active on the hardware output:    //      use device for strategy DTMF// isInCall 函数的作用是判断当前状态是否是有电话打过来，或者正处于通话中    if (isInCall() ||// isUsedByStrategy 函数的功能是返回该 output 中指定 strategy 对应的所有 stream 的引用总和。// 简单一点就是判断该 output 中是否使用了指定的 strategy 。        outputDesc->isUsedByStrategy(STRATEGY_PHONE)) {        device = getDeviceForStrategy(STRATEGY_PHONE, fromCache);    } else if (outputDesc->isUsedByStrategy(STRATEGY_SONIFICATION)) {        device = getDeviceForStrategy(STRATEGY_SONIFICATION, fromCache);    } else if (outputDesc->isUsedByStrategy(STRATEGY_MEDIA)) {        device = getDeviceForStrategy(STRATEGY_MEDIA, fromCache);    } else if (outputDesc->isUsedByStrategy(STRATEGY_DTMF)) {        device = getDeviceForStrategy(STRATEGY_DTMF, fromCache);    }    LOGV("getNewDevice() selected device %x", device);    return device;}void AudioPolicyManagerBase::setOutputDevice(audio_io_handle_t output, uint32_t device, bool force, int delayMs){    LOGV("setOutputDevice() output %d device %x delayMs %d", output, device, delayMs);    AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output);    if (outputDesc->isDuplicated()) {        setOutputDevice(outputDesc->mOutput1->mId, device, force, delayMs);        setOutputDevice(outputDesc->mOutput2->mId, device, force, delayMs);        return;    }#ifdef WITH_A2DP    // filter devices according to output selected    if (output == mA2dpOutput) {        device &= AudioSystem::DEVICE_OUT_ALL_A2DP;    } else {        device &= ~AudioSystem::DEVICE_OUT_ALL_A2DP;    }#endif// 函数 device 返回其成员变量 mDevice// mDevice 在 AudioPolicyManagerBase 的构造函数或函数 AudioPolicyManagerBase::getOutput 中被赋值    uint32_t prevDevice = (uint32_t)outputDesc->device();    // Do not change the routing if:    //  - the requestede device is 0    //  - the requested device is the same as current device and force is not specified.    // Doing this check here allows the caller to call setOutputDevice() without conditions// 若可用的 device 只有耳机，此时正在听歌，若有电话打过来，找到的 device 也是耳机，// 所以并不会作 route 的切换，但我们需要在打电话的时候把音乐停掉，这个处理不在这儿    if ((device == 0 || device == prevDevice) && !force) {        LOGV("setOutputDevice() setting same device %x or null device for output %d", device, output);        return;    }    outputDesc->mDevice = device;    // mute media streams if both speaker and headset are selected    if (output == mHardwareOutput && AudioSystem::popCount(device) == 2) {        setStrategyMute(STRATEGY_MEDIA, true, output);        // wait for the PCM output buffers to empty before proceeding with the rest of the command        usleep(outputDesc->mLatency*2*1000);    }    // do the routing    AudioParameter param = AudioParameter();    param.addInt(String8(AudioParameter::keyRouting), (int)device);// 改变 route ，最终会掉到 ALSAControl 中的 set 函数来设置 codec 的 switch 或者 widget 。    mpClientInterface->setParameters(mHardwareOutput, param.toString(), delayMs);    // update stream volumes according to new device// 设置 device 上各 stream 对应的音量// 其中的实现是遍历各 stream ，调用函数 checkAndSetVolume 将 AudioOutputDescriptor 保存的各 stream 的音量进行设置// checkAndSetVolume 函数的实现在后面有看    applyStreamVolumes(output, device, delayMs);    // if changing from a combined headset + speaker route, unmute media streams    if (output == mHardwareOutput && AudioSystem::popCount(prevDevice) == 2) {        setStrategyMute(STRATEGY_MEDIA, false, output, delayMs);    }}status_t AudioPolicyManagerBase::checkAndSetVolume(int stream, int index, audio_io_handle_t output, uint32_t device, int delayMs, bool force){    // do not change actual stream volume if the stream is muted    if (mOutputs.valueFor(output)->mMuteCount[stream] != 0) {        LOGV("checkAndSetVolume() stream %d muted count %d", stream, mOutputs.valueFor(output)->mMuteCount[stream]);        return NO_ERROR;    }    // do not change in call volume if bluetooth is connected and vice versa    if ((stream == AudioSystem::VOICE_CALL && mForceUse[AudioSystem::FOR_COMMUNICATION] == AudioSystem::FORCE_BT_SCO) ||        (stream == AudioSystem::BLUETOOTH_SCO && mForceUse[AudioSystem::FOR_COMMUNICATION] != AudioSystem::FORCE_BT_SCO)) {        LOGV("checkAndSetVolume() cannot set stream %d volume with force use = %d for comm",             stream, mForceUse[AudioSystem::FOR_COMMUNICATION]);        return INVALID_OPERATION;    }    float volume = computeVolume(stream, index, output, device);    // We actually change the volume if:    // - the float value returned by computeVolume() changed    // - the force flag is set    if (volume != mOutputs.valueFor(output)->mCurVolume[stream] ||            force) {        mOutputs.valueFor(output)->mCurVolume[stream] = volume;        LOGV("setStreamVolume() for output %d stream %d, volume %f, delay %d", output, stream, volume, delayMs);        if (stream == AudioSystem::VOICE_CALL ||            stream == AudioSystem::DTMF ||            stream == AudioSystem::BLUETOOTH_SCO) {            // offset value to reflect actual hardware volume that never reaches 0            // 1% corresponds roughly to first step in VOICE_CALL stream volume setting (see AudioService.java)            volume = 0.01 + 0.99 * volume;        }        mpClientInterface->setStreamVolume((AudioSystem::stream_type)stream, volume, output, delayMs);    }    if (stream == AudioSystem::VOICE_CALL ||        stream == AudioSystem::BLUETOOTH_SCO) {        float voiceVolume;        // Force voice volume to max for bluetooth SCO as volume is managed by the headset        if (stream == AudioSystem::VOICE_CALL) {            voiceVolume = (float)index/(float)mStreams[stream].mIndexMax;        } else {            voiceVolume = 1.0;        }        if (voiceVolume != mLastVoiceVolume && output == mHardwareOutput) {            mpClientInterface->setVoiceVolume(voiceVolume, delayMs);            mLastVoiceVolume = voiceVolume;        }    }    return NO_ERROR;}float AudioPolicyManagerBase::computeVolume(int stream, int index, audio_io_handle_t output, uint32_t device){    float volume = 1.0;    AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output);    StreamDescriptor &streamDesc = mStreams[stream];    if (device == 0) {        device = outputDesc->device();    }    int volInt = (100 * (index - streamDesc.mIndexMin)) / (streamDesc.mIndexMax - streamDesc.mIndexMin);    volume = AudioSystem::linearToLog(volInt);    // if a headset is connected, apply the following rules to ring tones and notifications    // to avoid sound level bursts in user's ears:    // - always attenuate ring tones and notifications volume by 6dB    // - if music is playing, always limit the volume to current music volume,    // with a minimum threshold at -36dB so that notification is always perceived.    if ((device &        (AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP |        AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |        AudioSystem::DEVICE_OUT_WIRED_HEADSET |        AudioSystem::DEVICE_OUT_WIRED_HEADPHONE)) &&        ((getStrategy((AudioSystem::stream_type)stream) == STRATEGY_SONIFICATION) ||         (stream == AudioSystem::SYSTEM)) &&        streamDesc.mCanBeMuted) {        volume *= SONIFICATION_HEADSET_VOLUME_FACTOR;        // when the phone is ringing we must consider that music could have been paused just before        // by the music application and behave as if music was active if the last music track was        // just stopped        if (outputDesc->mRefCount[AudioSystem::MUSIC] || mLimitRingtoneVolume) {            float musicVol = computeVolume(AudioSystem::MUSIC, mStreams[AudioSystem::MUSIC].mIndexCur, output, device);            float minVol = (musicVol > SONIFICATION_HEADSET_VOLUME_MIN) ? musicVol : SONIFICATION_HEADSET_VOLUME_MIN;            if (volume > minVol) {                volume = minVol;                LOGV("computeVolume limiting volume to %f musicVol %f", minVol, musicVol);            }        }    }    return volume;}

1、 strategy 之间的优先级只有在不同的 strategy 可以找到不同的可以 device 时才会发挥作用。
如，原来在听音乐，使用的是 speaker ，此时有电话打过来，使用的是另外一个 device ，此时就需要改变 route 。
如果原来在打电话，此时打开音乐，使用的设备其实是 phone strategy 使用的 device 。
至于有电话打进的时候，正在播放的音乐是停止还是 mute ，native 代码中好像没有做处理。

2、 native 中对各 stream 的音量并没有做优先级的处理。
只有在连接耳机的时候会对 STRATEGY_SONIFICATION 和 SYSTEM stream 的音量进行一定的处理。