Android 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。