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。