Android(安卓)4.4KitKat AudioFlinger 流程分析

AudioFlinger(AF)是一个服务,具体的启动代码在av\media\mediaserver\Main_mediaserver.cpp中：

int main(int argc, char** argv){    signal(SIGPIPE, SIG_IGN);    char value[PROPERTY_VALUE_MAX];    bool doLog = (property_get("ro.test_harness", value, "0") > 0) && (atoi(value) == 1);    pid_t childPid;    // FIXME The advantage of making the process containing media.log service the parent process of    // the process that contains all the other real services, is that it allows us to collect more    // detailed information such as signal numbers, stop and continue, resource usage, etc.    // But it is also more complex.  Consider replacing this by independent processes, and using    // binder on death notification instead.    if (doLog && (childPid = fork()) != 0) {        // media.log service        //prctl(PR_SET_NAME, (unsigned long) "media.log", 0, 0, 0);        // unfortunately ps ignores PR_SET_NAME for the main thread, so use this ugly hack        strcpy(argv[0], "media.log");        sp<ProcessState> proc(ProcessState::self());        MediaLogService::instantiate();        ProcessState::self()->startThreadPool();        ......
　　　　　sp<ProcessState> proc(ProcessState::self());        sp<IServiceManager> sm = defaultServiceManager();        ALOGI("ServiceManager: %p", sm.get());        AudioFlinger::instantiate();        MediaPlayerService::instantiate();        CameraService::instantiate();        AudioPolicyService::instantiate();        registerExtensions();        ProcessState::self()->startThreadPool();        IPCThreadState::self()->joinThreadPool();    }}

追踪AudioFlinger::instantiate()函数的实现可到native\include\binder\BinderService.h中的

static status_t publish(bool allowIsolated = false) {        sp<IServiceManager> sm(defaultServiceManager());        return sm->addService( String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);     }
static void instantiate() { publish(); }

然后再往哪儿追踪代码就不知道了，没那个时间，不要在意细节，继续看AudioFlinger的构造函数：

AudioFlinger::AudioFlinger()    : BnAudioFlinger(),//初始化基类      mPrimaryHardwareDev(NULL),      mHardwareStatus(AUDIO_HW_IDLE),      mMasterVolume(1.0f),      mMasterMute(false),      mNextUniqueId(1),      mMode(AUDIO_MODE_INVALID),      mBtNrecIsOff(false),      mIsLowRamDevice(true),      mIsDeviceTypeKnown(false),      mGlobalEffectEnableTime(0){    getpid_cached = getpid();    char value[PROPERTY_VALUE_MAX];    bool doLog = (property_get("ro.test_harness", value, "0") > 0) && (atoi(value) == 1);    if (doLog) {        mLogMemoryDealer = new MemoryDealer(kLogMemorySize, "LogWriters");    }#ifdef TEE_SINK    (void) property_get("ro.debuggable", value, "0");    int debuggable = atoi(value);    int teeEnabled = 0;    if (debuggable) {        (void) property_get("af.tee", value, "0");        teeEnabled = atoi(value);    }    if (teeEnabled & 1)        mTeeSinkInputEnabled = true;    if (teeEnabled & 2)        mTeeSinkOutputEnabled = true;    if (teeEnabled & 4)        mTeeSinkTrackEnabled = true;#endif}

设置硬件的各种属性状态。

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