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本篇內(nèi)容介紹了“Camera Service的結(jié)構(gòu)是什么”的有關(guān)知識(shí),在實(shí)際案例的操作過程中,不少人都會(huì)遇到這樣的困境,接下來就讓小編帶領(lǐng)大家學(xué)習(xí)一下如何處理這些情況吧!希望大家仔細(xì)閱讀,能夠?qū)W有所成!
在camera service這端的結(jié)構(gòu)還是很容易讓人迷惑的,我就是看了好久,才縷清楚關(guān)系。
service這部分包括以下幾個(gè)頭文件:ICamera.h, ICameraService.h, CameraService.h,對(duì)應(yīng)的實(shí)現(xiàn)ICamera.cpp, ICameraService.cpp, CameraService.cpp。
CameraService中包含了一個(gè)內(nèi)部類CameraService::Client,這個(gè)CameraService::Client是對(duì)ICamera的實(shí)現(xiàn),camera client得到的ICamera就是這個(gè)CameraService::Client。
也就是說與camera client真正通信的,是這個(gè)CameraService::Client。下面我們來逐步分析service這塊的實(shí)現(xiàn)。
1.ICameraService
(1)ICameraService.h
其中只定義了3個(gè)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(gè)函數(shù)的真正實(shí)現(xiàn)在CameraService.cpp中。
sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder());中得到此次連接的client,并且傳遞到connect函數(shù)中。保存client信息的目的是保存在CameraService::Client中,在適當(dāng)?shù)臅r(shí)機(jī)回調(diào)client。
2.CameraService
(1)CameraService.h
class CameraService : public BinderService<CameraService>, public BnCameraService
這個(gè) BinderService<CameraService>是什么東西呢?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注冊。
其實(shí)這個(gè)模板類,就是為native service提供了一向service注冊的統(tǒng)一方式。
publish和publishAndJoinThreadPool的區(qū)別就是在于,注冊之后是否開啟線程池來監(jiān)聽。
因?yàn)橹翱催^media server的代碼,在media server的main函數(shù)里,調(diào)用的就是CameraService.instantiate來注冊的,因?yàn)閏amera service是跑在media server進(jìn)程里的,所以camera service不需要自己來開啟線程來循環(huán)監(jiān)聽。
所以,我覺得調(diào)用publish和publishAndJoinThreadPool的不同場景是:如果這個(gè)service是跑在別的進(jìn)程里的,就調(diào)用publish,如果是自己單獨(dú)一個(gè)進(jìn)程,就調(diào)用publishAndJoinThreadPool。
(2)CameraService.cpp
實(shí)現(xiàn)在ICameraService定義的3個(gè)函數(shù)。
getNumberOfCameras()和getCameraInfo()的實(shí)現(xiàn)很簡單。
int32_t CameraService::getNumberOfCameras() {
return mNumberOfCameras; //mNumberOfCameras是在構(gòu)造函數(shù)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(shù):
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(gòu)造Client時(shí)傳遞進(jìn)入
…………
CameraInfo info;
HAL_getCameraInfo(cameraId, &info);
client = new Client(this, cameraClient, hardware, cameraId, info.facing, callingPid); //這里就是之前說過的,在onTransact保存的client
mClient[cameraId] = client;
return client;
}
3.CameraService::Client
class Client : public BnCamera, Client是對(duì)ICamera的實(shí)現(xiàn)。
構(gòu)造函數(shù):
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(jìn)行一些成員變量的初始化,主要有mCameraClient, mHardware等。都是在CameraService::connect時(shí)進(jìn)行的。
Client的各個(gè)函數(shù)可以自己看一下,主要就是對(duì)mHardware的調(diào)用,這是一個(gè)CameraHardwareInterface接口,也就是對(duì)HAL層的一個(gè)封裝。比如stopRecording函數(shù):
// stop recording mode
void CameraService::Client::stopRecording() {
……
mCameraService->playSound(SOUND_RECORDING);
disableMsgType(CAMERA_MSG_VIDEO_FRAME);
mHardware->stopRecording();
…………
}
4.ICamera
最后再來說一下ICamera。
這個(gè)ICamera定義的其實(shí)就是camera client與camera service的接口。
當(dāng)camera client連接camera service時(shí),也就是調(diào)用CameraService::connect時(shí),返回一個(gè)ICamera接口給camera client調(diào)用,這個(gè)ICamera接口的真正實(shí)現(xiàn)是CameraService::Client。
“Camera Service的結(jié)構(gòu)是什么”的內(nèi)容就介紹到這里了,感謝大家的閱讀。如果想了解更多行業(yè)相關(guān)的知識(shí)可以關(guān)注億速云網(wǎng)站,小編將為大家輸出更多高質(zhì)量的實(shí)用文章!
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