Camera Service的結構是什么

本篇內容介紹了“Camera Service的結構是什么”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！

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，才縷清楚關系。

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，并且傳遞到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。

其實這個模板類，就是為native service提供了一向service注冊的統一方式。

publish和publishAndJoinThreadPool的區別就是在于，注冊之后是否開啟線程池來監聽。

因為之前看過media server的代碼，在media server的main函數里，調用的就是CameraService.instantiate來注冊的，因為camera service是跑在media server進程里的，所以camera service不需要自己來開啟線程來循環監聽。

所以，我覺得調用publish和publishAndJoinThreadPool的不同場景是：如果這個service是跑在別的進程里的，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

最后再來說一下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。

“Camera Service的結構是什么”的內容就介紹到這里了，感謝大家的閱讀。如果想了解更多行業相關的知識可以關注億速云網站，小編將為大家輸出更多高質量的實用文章！