Android Audio Subsystem - get_audio_flinger - 01
1． AudioSystem::get_audio_flinger()
Frameworks/av/media/libmedia/AudioSystem.cpp
constsp<IAudioFlinger>& AudioSystem::get_audio_flinger()
{
Mutex::Autolock _l(gLock);
if (gAudioFlinger == 0) {
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
do {
binder =sm->getService(String16("media.audio_flinger"));
if (binder != 0)
break;
ALOGW("AudioFlinger notpublished, waiting...");
usleep(500000); // 0.5 s
} while (true);
if (gAudioFlingerClient == NULL) {
gAudioFlingerClient = new AudioFlingerClient();
} else {
if (gAudioErrorCallback) {
gAudioErrorCallback(NO_ERROR);
}
}
binder->linkToDeath(gAudioFlingerClient);
gAudioFlinger =interface_cast<IAudioFlinger>(binder);
gAudioFlinger->registerClient(gAudioFlingerClient);
}
ALOGE_IF(gAudioFlinger==0, "noAudioFlinger!?");
return gAudioFlinger;
}
2． sp<IServiceManager>defaultServiceManager()
Frameworks/native/libs/binder/IServiceManager.cpp
sp<IServiceManager> defaultServiceManager()
{
if (gDefaultServiceManager!= NULL) return gDefaultServiceManager;
{
AutoMutex_l(gDefaultServiceManagerLock);
if(gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
}
}
returngDefaultServiceManager;
}
3． sp<ProcessState>ProcessState::self()
Frameworks/native/libs/binder/ProcessState.cpp
sp<ProcessState> ProcessState::self()
{
Mutex::Autolock _l(gProcessMutex);
if (gProcess != NULL) {
return gProcess;
}
gProcess= new ProcessState;
return gProcess;
}
4． sp<ProcessState>ProcessState::self()
Frameworks/native/libs/binder/ProcessState.cpp
ProcessState::ProcessState()
: mDriverFD(open_driver())
, mVMStart(MAP_FAILED)
, mManagesContexts(false)
,mBinderContextCheckFunc(NULL)
,mBinderContextUserData(NULL)
,mThreadPoolStarted(false)
, mThreadPoolSeq(1)
{
if (mDriverFD >= 0) {
// XXX Ideally, thereshould be a specific define for whether we
// have mmap (orwhether we could possibly have the kernel module
// availabla).
#if !defined(HAVE_WIN32_IPC)
// mmap the binder,providing a chunk of virtual address space to receive transactions.
mVMStart = mmap(0,BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);
if (mVMStart ==MAP_FAILED) {
// *sigh*
ALOGE("Using/dev/binder failed: unable to mmap transaction memory.\n");
close(mDriverFD);
mDriverFD = -1;
}
#else
mDriverFD = -1;
#endif
}
LOG_ALWAYS_FATAL_IF(mDriverFD < 0, "Binder driver could not beopened. Terminating.");
}
5． sp<ProcessState>ProcessState::self()
Frameworks/native/libs/binder/ProcessState.cpp
sp<IBinder> ProcessState::getContextObject(constsp<IBinder>& caller)
{
returngetStrongProxyForHandle(0);
}
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_thandle)
{
sp<IBinder> result;
AutoMutex _l(mLock);
handle_entry* e =lookupHandleLocked(handle);
if (e != NULL) {
// We need to create anew BpBinder if there isn't currently one, OR we
// are unable toacquire a weak reference on this current one. See comment
// ingetWeakProxyForHandle() for more info about this.
IBinder* b =e->binder;
if (b == NULL ||!e->refs->attemptIncWeak(this)) {
b = newBpBinder(handle);
e->binder = b;
if (b) e->refs= b->getWeakRefs();
result = b;
} else {
// This little bitof nastyness is to allow us to add a primary
// reference tothe remote proxy when this team doesn't have one
// but anotherteam is sending the handle to us.
result.force_set(b);
e->refs->decWeak(this);
}
}
return result; // 返回BpBinder(handle); 且handle为0，代表ServiceManager
}
6． interface_cast<IServiceManager>(BpBinder(handle))
frameworks/native/libs/binder/IInterface.h
android::sp<I##INTERFACE> I##INTERFACE::asInterface( \
constandroid::sp<android::IBinder>& obj) \
{ \
android::sp<I##INTERFACE> intr; \
if (obj != NULL){ \
intr =static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL){ \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \
在这个函数里，将作如下事情：
1.) 查询BpBinder(0)的本地接口，这儿应该返回NULL
2.) NewBpServiceManager(BpBinder(0))对象并返回这个对象
3.) BpServiceManager的mRemote将指向BpBinder(0)
7． BpServiceManager::getService()
Frameworks/native/libs/binder/IServiceManager.cpp
virtual sp<IBinder> getService(constString16& name) const
{
unsigned n;
for (n = 0; n < 5; n++){
sp<IBinder> svc = checkService(name);
if (svc != NULL) return svc;
ALOGI("Waiting for service%s...\n", String8(name).string());
sleep(1);
}
return NULL;
}
virtual sp<IBinder> checkService( const String16& name) const
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeString16(name);
remote()->transact(CHECK_SERVICE_TRANSACTION, data, &reply);
return reply.readStrongBinder();
}
// 这儿remote()返回的是BpServiceManager::mRemote成员变量，
// 它指向的是前面defaultServiceManager()过程中 BpBinder(0)对象。
// 因此调用的是BpBinder::transact()
8． BpBinder::transact()
status_tBpBinder::transact(
uint32_t code, const Parcel& data,Parcel* reply, uint32_t flags)
{
// Once a binder has died, it will nevercome back to life.
if (mAlive) {
//这儿将创建一个新的IPCThreadState,
// 每个线程都有一个IPCThreadState实例，都有一个mIn, mOut
// mIn用来接收来自binder设备的数据，
//而mOut用来存储发往binder设备的数据
status_t status= IPCThreadState::self()->transact(
mHandle,code, data, reply, flags);
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
}
9． IPCThreadState*IPCThreadState::self()
Frameworks/native/libs/binder/IPCThreadState.cpp
IPCThreadState*IPCThreadState::self()
{
if (gHaveTLS) {
restart:
const pthread_key_t k = gTLS;
IPCThreadState* st =(IPCThreadState*)pthread_getspecific(k);
if (st) return st;
return new IPCThreadState;
}
if (gShutdown) return NULL;
pthread_mutex_lock(&gTLSMutex);
if (!gHaveTLS) {
if (pthread_key_create(&gTLS,threadDestructor) != 0) {
pthread_mutex_unlock(&gTLSMutex);
return NULL;
}
gHaveTLS = true;
}
pthread_mutex_unlock(&gTLSMutex);
goto restart;
}
IPCThreadState::IPCThreadState()
: mProcess(ProcessState::self()),
mMyThreadId(androidGetTid()),
mStrictModePolicy(0),
mLastTransactionBinderFlags(0)
{
pthread_setspecific(gTLS, this);
clearCaller();
mIn.setDataCapacity(256);
mOut.setDataCapacity(256);
}