Android IPC 通讯机制源码分析

核心提示：ProcessState::self()->startThreadPool(); //为进程开启缓冲池IPCThreadState::self()->joinThreadPool(); //将进程加入到缓冲池}CameraService.cppvoid CameraService::instantiate(

ProcessState::self()->startThreadPool(); //为进程开启缓冲池

IPCThreadState::self()->joinThreadPool(); //将进程加入到缓冲池

}

CameraService.cpp

void CameraService::instantiate() {

defaultServiceManager()->addService(

String16("media.camera"), new CameraService());

}

创建CameraService服务对象并添加到ServiceManager进程中。

client获取remote IServiceManager IBinder接口：

sp defaultServiceManager()

{

if (gDefaultServiceManager != NULL) return gDefaultServiceManager;

{

AutoMutex _l(gDefaultServiceManagerLock);

if (gDefaultServiceManager == NULL) {

gDefaultServiceManager = interface_cast(

ProcessState::self()->getContextObject(NULL));

}

}

return gDefaultServiceManager;

}

任何一个进程在第一次调用defaultServiceManager的时候gDefaultServiceManager值为Null，所以该进程会通过ProcessState::self得到ProcessState实例。ProcessState将打开Binder驱动。

ProcessState.cpp

sp ProcessState::self()

{

if (gProcess != NULL) return gProcess;

AutoMutex _l(gProcessMutex);

if (gProcess == NULL) gProcess = new ProcessState;

return gProcess;

}

ProcessState::ProcessState()

: mDriverFD(open_driver()) //打开/dev/binder驱动

...........................

{

}

sp ProcessState::getContextObject(const sp& caller)

{

if (supportsProcesses()) {

return getStrongProxyForHandle(0);

} else {

return getContextObject(String16("default"), caller);

}

}

Android是支持Binder驱动的所以程序会调用getStrongProxyForHandle。这里handle为0，正好与Service_manager中的BINDER_SERVICE_MANAGER一致。