目前在調查AudioFlinger，想做到從一個裝置輸出到輸出到兩個裝置的轉換。面臨以下問題：

1，  某個thread如何改變某個playback執行緒的輸出route.

根據調查的結果，這個route只支援在同一個裝置上的切換，比如在primary裝置內部切換路由, 從DAC0切到DAC1等等。不支援多個裝置間的路由的切換。

2，  當thread路由變化後，如何將已經加入的track從一個執行緒移動到另一個執行緒

關於這塊，我從程式碼中無法看出是啥時候做了這件事，但是經過測試後，發現其還真是支援track的移動。所以就掛上gdbserver來檢視。列印的backtrace如下：

(gdb) break /home/wqw/Projects/KM500/frameworks/av/services/audioflinger/AudioFlinger.cpp:461

Breakpoint 1 at 0x4007fe36: file frameworks/av/services/audioflinger/AudioFlinger.cpp, line 461.

(gdb) c

Continuing.

[New Thread 3411]

[Switching to Thread 3411]

Breakpoint 1, android::AudioFlinger::createTrack (this=0x40f4a078, pid=2234, streamType=AUDIO_STREAM_MIX, sampleRate=48000,

    format=AUDIO_FORMAT_PCM_16_BIT, channelMask=3, frameCount=3343, flags=0, sharedBuffer=..., output=6, tid=-1, sessionId=0x41439d3c,

    status=0x43d95cf8) at frameworks/av/services/audioflinger/AudioFlinger.cpp:469

469             if (uint32_t(streamType) >= AUDIO_STREAM_CNT) {

(gdb) bt

#0  android::AudioFlinger::createTrack (this=0x40f4a078, pid=2234, streamType=AUDIO_STREAM_MIX, sampleRate=48000,

    format=AUDIO_FORMAT_PCM_16_BIT, channelMask=3, frameCount=3343, flags=0, sharedBuffer=..., output=6, tid=-1, sessionId=0x41439d3c,

    status=0x43d95cf8) at frameworks/av/services/audioflinger/AudioFlinger.cpp:469

#1  0x4025e502 in android::AudioTrack::createTrack_l (this=0x41439cc8, streamType=AUDIO_STREAM_MIX, sampleRate=48000,

    format=AUDIO_FORMAT_PCM_16_BIT, channelMask=3, frameCount=<optimized out>, flags=AUDIO_OUTPUT_FLAG_NONE, sharedBuffer=..., output=6)

    at frameworks/av/media/libmedia/AudioTrack.cpp:899

#2  0x4025e71e in android::AudioTrack::restoreTrack_l (this=0x41439cc8, [email protected], fromStart=<optimized out>)

    at frameworks/av/media/libmedia/AudioTrack.cpp:1364

#3  0x4025ea9c in android::AudioTrack::obtainBuffer (this=0x41439cc8, audioBuffer=0x43d95df0, waitCount=-1)

    at frameworks/av/media/libmedia/AudioTrack.cpp:1015

#4  0x4025f360 in android::AudioTrack::write (this=0x41439cc8, buffer=<optimized out>, userSize=3340)

    at frameworks/av/media/libmedia/AudioTrack.cpp:1116

#5  0x405d37a4 in android::MediaPlayerService::AudioOutput::write (this=0x400dcc68, buffer=<optimized out>, size=<optimized out>)

    at frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp:1665

#6  0x413696d2 in android::AndroidAudioRender::WriteDevice (this=0x411a69f8,

    pBuffer=0x413ef5a4 "\320\016A\377\031\a\367\375\261\377j\374J\374\345\371\372\375\234\370S", nActuralLen=3340)

    at external/fsl_imx_omx/OpenMAXIL/src/component/android_audio_render/AndroidAudioRender.cpp:374

#7  0x411e29a2 in AudioRender::RenderPeriod (this=0x411a69f8) at external/fsl_imx_omx/OpenMAXIL/src/component/common/AudioRender.cpp:667

#8  0x411e2f6a in RenderData (this=0x411a69f8) at external/fsl_imx_omx/OpenMAXIL/src/component/common/AudioRender.cpp:634

#9  AudioRender::RenderData (this=0x411a69f8) at external/fsl_imx_omx/OpenMAXIL/src/component/common/AudioRender.cpp:624

#10 0x411e33c4 in AudioRender::ProcessDataBuffer (this=0x411a69f8)

    at external/fsl_imx_omx/OpenMAXIL/src/component/common/AudioRender.cpp:318

#11 0x411dbc22 in ProcessBuffer (this=0x41316030) at external/fsl_imx_omx/OpenMAXIL/src/component/common/ExecutingState.cpp:48

#12 ExecutingState::ProcessBuffer (this=0x41316030) at external/fsl_imx_omx/OpenMAXIL/src/component/common/ExecutingState.cpp:42

#13 0x411db7a4 in DoThread (arg=0x411a69f8) at external/fsl_imx_omx/OpenMAXIL/src/component/common/ComponentBase.cpp:570

#14 0x400eb3fc in __thread_entry (func=0x411db749 <DoThread(void*)>, arg=0x411a69f8, tls=0x43d95f00) at bionic/libc/bionic/pthread.c:204

#15 0x400eaae8 in pthread_create (thread_out=0x43d95f00, attr=0x4011f1e0, start_routine=0x411db749 <DoThread(void*)>, arg=<optimized out>)

at bionic/libc/bionic/pthread.c:348

其基本的流程是: MediaPlayer呼叫AudioTrack的write函式à呼叫obtain buffer獲取可寫記憶體à發現TRACK的FLAG設為CBLK_INVALID_ON後，變會呼叫

restoreTrack_l-à restoreTrack_l內部會呼叫AudioFlinger::createTrack建立一個新的，並放到合適的thread中。

另外，這個FLAG是在改變路由時，將這些不符合條件的track打上CBLK_INVALID_ON的標識的，log如下：

D/AudioPolicyManagerBase( 2234): checkAndSetVolume() cannot set stream 6 volume with force use = 0 for comm

D/qwang   ( 2234): setStreamOutput() stream 10 to output 6

D/qwang   ( 2234): MixerThread::invalidateTracks() mixer 0x40f4d330, streamType 10, mTracks.size 0

D/qwang   ( 2234): MixerThread::invalidateTracks() mixer 0x40f2a008, streamType 10, mTracks.size 3

D/qwang   ( 2234): MixerThread::invalidateTracks() mixer 0x4134a008, streamType 10, mTracks.size 1

D/qwang   ( 2234): MixerThread::invalidateTracks() mixer 0x41791008, streamType 10, mTracks.size 1