在camera service這端的結構還是很容易讓人迷惑的，我就是看了好久，才縷清楚關係。
service這部分包括以下幾個頭文件：ICamera.h, ICameraService.h, CameraService.h，對應的實現ICamera.cpp, ICameraService.cpp, CameraService.cpp。
CameraService中包含了一個內部類CameraService::Client，這個CameraService::Client是對ICamera的實現，camera client得到的ICamera就是這個CameraService::Client。
也就是說與camera client真正通信的，是這個CameraService::Client。下面我們來逐步分析service這塊的實現。
1.ICameraService
（1）ICameraService.h
其中只定義了3個方法：
virtual int32_t getNumberOfCameras() = 0;
virtual status_t getCameraInfo(int cameraId, struct CameraInfo* cameraInfo) = 0;
virtual sp<ICamera> connect(const sp<ICameraClient>& cameraClient, int cameraId) = 0;
（2） ICameraService.cpp
看代碼：
status_t BnCameraService::onTransact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
case GET_NUMBER_OF_CAMERAS: {
CHECK_INTERFACE(ICameraService, data, reply);
reply->writeInt32(getNumberOfCameras());
return NO_ERROR;
} break;
case GET_CAMERA_INFO: {
CHECK_INTERFACE(ICameraService, data, reply);
CameraInfo cameraInfo;
memset(&cameraInfo, 0, sizeof(cameraInfo));
status_t result = getCameraInfo(data.readInt32(), &cameraInfo);
reply->writeInt32(cameraInfo.facing);
reply->writeInt32(cameraInfo.orientation);
reply->writeInt32(result);
return NO_ERROR;
} break;
case CONNECT: {
CHECK_INTERFACE(ICameraService, data, reply);
sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder());
sp<ICamera> camera = connect(cameraClient, data.readInt32());
reply->writeStrongBinder(camera->asBinder());
return NO_ERROR;
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
這3個函數的真正實現在CameraService.cpp中。
sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder());中得到此次連接的client，並且傳遞到connect函數中。保存client信息的目的是保存在CameraService::Client中，在適當的時機回調client。
2.CameraService
（1）CameraService.h
class CameraService : public BinderService<CameraService>, public BnCameraService
這個 BinderService<CameraService>是什麼東西呢？看看它的定義，在frameworks/base/include/binder下BinderService.h。
template<typename SERVICE>
class BinderService
{
public:
static status_t publish() {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE());
}
static void publishAndJoinThreadPool() {
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SERVICE::getServiceName()), new SERVICE());
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
static void instantiate() { publish(); }
static status_t shutdown() {
return NO_ERROR;
}
};
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE());從這句代碼，可以看出，這是native service在向SM註冊。
其實這個模板類，就是爲native service提供了一向service註冊的統一方式。
publish和publishAndJoinThreadPool的區別就是在於，註冊之後是否開啓線程池來監聽。
因爲之前看過media server的代碼，在media server的main函數裏，調用的就是CameraService.instantiate來註冊的，因爲camera service是跑在media server進程裏的，所以camera service不需要自己來開啓線程來循環監聽。
所以，我覺得調用publish和publishAndJoinThreadPool的不同場景是：如果這個service是跑在別的進程裏的，就調用publish，如果是自己單獨一個進程，就調用publishAndJoinThreadPool。
（2）CameraService.cpp
實現在ICameraService定義的3個函數。
getNumberOfCameras（）和getCameraInfo（）的實現很簡單。
int32_t CameraService::getNumberOfCameras() {
return mNumberOfCameras; //mNumberOfCameras是在構造函數中初始化的，mNumberOfCameras = HAL_getNumberOfCameras();
}
status_t CameraService::getCameraInfo(int cameraId,
struct CameraInfo* cameraInfo) {
if (cameraId < 0 || cameraId >= mNumberOfCameras) {
return BAD_VALUE;
}
HAL_getCameraInfo(cameraId, cameraInfo);
return OK;
}
主要看connect函數：
sp<ICamera> CameraService::connect( const sp<ICameraClient>& cameraClient, int cameraId) {
sp<Client> client; //CameraService::Client
…………
if (mClient[cameraId] != 0) {
client = mClient[cameraId].promote();
if (client != 0) {
if (cameraClient->asBinder() == client->getCameraClient()->asBinder()) {
LOG1("CameraService::connect X (pid %d) (the same client)",
callingPid);
return client;
}
}
}
…………
sp<CameraHardwareInterface> hardware = HAL_openCameraHardware(cameraId); //獲取CameraHardwareInterface接口，在下邊的代碼構造Client時傳遞進入
…………
CameraInfo info;
HAL_getCameraInfo(cameraId, &info);
client = new Client(this, cameraClient, hardware, cameraId, info.facing, callingPid); //這裏就是之前說過的，在onTransact保存的client
mClient[cameraId] = client;
return client;
}
3.CameraService::Client
class Client : public BnCamera， Client是對ICamera的實現。
構造函數：
CameraService::Client::Client(const sp<CameraService>& cameraService,
const sp<ICameraClient>& cameraClient,
const sp<CameraHardwareInterface>& hardware,
int cameraId, int cameraFacing, int clientPid) {
int callingPid = getCallingPid();
LOG1("Client::Client E (pid %d)", callingPid);
mCameraService = cameraService;
mCameraClient = cameraClient;
mHardware = hardware;
mCameraId = cameraId;
mCameraFacing = cameraFacing;
mClientPid = clientPid;
mUseOverlay = mHardware->useOverlay();
mMsgEnabled = 0;
mHardware->setCallbacks(notifyCallback,
dataCallback,
dataCallbackTimestamp,
(void *)cameraId);
// Enable zoom, error, and focus messages by default
enableMsgType(CAMERA_MSG_ERROR |
CAMERA_MSG_ZOOM |
CAMERA_MSG_FOCUS);
mOverlayW = 0;
mOverlayH = 0;
// Callback is disabled by default
mPreviewCallbackFlag = FRAME_CALLBACK_FLAG_NOOP;
mOrientation = getOrientation(0, mCameraFacing == CAMERA_FACING_FRONT);
mOrientationChanged = false;
cameraService->setCameraBusy(cameraId);
cameraService->loadSound();
LOG1("Client::Client X (pid %d)", callingPid);
}
主要進行一些成員變量的初始化，主要有mCameraClient， mHardware等。都是在CameraService::connect時進行的。
Client的各個函數可以自己看一下，主要就是對mHardware的調用，這是一個CameraHardwareInterface接口，也就是對HAL層的一個封裝。比如stopRecording函數：
// stop recording mode
void CameraService::Client::stopRecording() {
……
mCameraService->playSound(SOUND_RECORDING);
disableMsgType(CAMERA_MSG_VIDEO_FRAME);
mHardware->stopRecording();
…………
}
4.ICamera
最後再來說一下ICamera。
這個ICamera定義的其實就是camera client與camera service的接口。
當camera client連接camera service時，也就是調用CameraService::connect時，返回一個ICamera接口給camera client調用，這個ICamera接口的真正實現是CameraService::Client。
