android camera运行流程

一 

首先既然Camera是利用binder通信，它肯定要将它的service注册到ServiceManager里面，以备后续Client引用，那么这一步是在哪里进行的呢？细心的人会发现，在frameworks\base\media\mediaserver\Main_MediaServer.cpp下有个main函数，可以用来注册媒体服务。没错就是在这里，CameraService完成了服务的注册,相关代码如下:

int main(int argc, char** argv)
{
    sp<ProcessState> proc(ProcessState::self());
    sp<IServiceManager> sm = defaultServiceManager();
    LOGI("ServiceManager: %p", sm.get());
    AudioFlinger::instantiate();
    MediaPlayerService::instantiate();
    CameraService::instantiate();
    AudioPolicyService::instantiate();
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();
}

可是我们到CameraService文件里面却找不到instantiate()这个函数，它在哪？继续追到它的一个父类BinderService,

CameraService的定义在frameworks/base/services/camera/libcameraservice/CameraService.h中

class CameraService :
    public BinderService<CameraService>,
    public BnCameraService
{
    class Client;
    friend class BinderService<CameraService>;
public:
    static char const* getServiceName() { return "media.camera"; }
    .....

    .....

}

从以上定义可以看出CameraService 继承于BinderService,所以CameraService::instantiate(); 其实是调用BinderService中的instantiate

BinderService的定义在frameworks/base/include/binder/BinderService.h中

// ---------------------------------------------------------------------------
namespace android {

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;
    }
};

}; // namespace android
// ---------------------------------------------------------------------------
可以发现在publish(）函数中，CameraService完成服务的注册 。这里面有个SERVICE，源码中有说明 

template<typename SERVICE>
这表示SERVICE是个模板，这里是注册CameraService，所以可以用CameraService代替
return sm->addService(String16(CameraService::getServiceName()), new CameraService());
好了这样，Camera就在ServiceManager完成服务注册，提供给client随时使用。
Main_MediaServer主函数由init.rc在启动是调用，所以在设备开机的时候Camera就会注册一个服务，用作binder通信。

二

Binder服务已注册，那接下来就看看client如何连上server端，并打开camera模块。咱们先从camera app的源码入手。在onCreate()函数中专门有一个open Camera的线程

camera app的源码文件在以下目录packages/apps/OMAPCamera/src/com/ti/omap4/android/camera/camera.java
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        getPreferredCameraId();
        String[] defaultFocusModes = getResources().getStringArray(
                R.array.pref_camera_focusmode_default_array);
        mFocusManager = new FocusManager(mPreferences, defaultFocusModes);


        /*
         * To reduce startup time, we start the camera open and preview threads.
         * We make sure the preview is started at the end of onCreate.
         */
        mCameraOpenThread.start();


        PreferenceInflater inflater = new PreferenceInflater(this);
        PreferenceGroup group =
                (PreferenceGroup) inflater.inflate(R.xml.camera_preferences);


        ListPreference gbce = group.findPreference(CameraSettings.KEY_GBCE);
        if (gbce != null) {
            mGBCEOff = gbce.findEntryValueByEntry(getString(R.string.pref_camera_gbce_entry_off));
            if (mGBCEOff == null) {
                mGBCEOff = "";
            }
        }


        ListPreference autoConvergencePreference = group.findPreference(CameraSettings.KEY_AUTO_CONVERGENCE);
        if (autoConvergencePreference != null) {
            mTouchConvergence = autoConvergencePreference.findEntryValueByEntry(getString(R.string.pref_camera_autoconvergence_entry_mode_touch));
            if (mTouchConvergence == null) {
                mTouchConvergence = "";
            }
            mManualConvergence = autoConvergencePreference.findEntryValueByEntry(getString(R.string.pref_camera_autoconvergence_entry_mode_manual));
            if (mManualConvergence == null) {
                mManualConvergence = "";
            }
        }


        ListPreference exposure = group.findPreference(CameraSettings.KEY_EXPOSURE_MODE_MENU);
        if (exposure != null) {
            mManualExposure = exposure.findEntryValueByEntry(getString(R.string.pref_camera_exposuremode_entry_manual));
            if (mManualExposure == null) {
                mManualExposure = "";
            }
        }


        ListPreference temp = group.findPreference(CameraSettings.KEY_MODE_MENU);
        if (temp != null) {
            mTemporalBracketing = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_temporal_bracketing));
            if (mTemporalBracketing == null) {
                mTemporalBracketing = "";
            }


            mExposureBracketing = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_exp_bracketing));
            if (mExposureBracketing == null) {
                mExposureBracketing = "";
            }


            mZoomBracketing = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_zoom_bracketing));
            if (mZoomBracketing == null) {
                mZoomBracketing = "";
            }


            mHighPerformance = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_hs));
            if (mHighPerformance == null) {
                mHighPerformance = "";
            }


            mHighQuality = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_hq));
            if (mHighQuality == null) {
                mHighQuality = "";
            }


            mHighQualityZsl = temp.findEntryValueByEntry(getString(R.string.pref_camera_mode_entry_zsl));
            if (mHighQualityZsl == null) {
                mHighQualityZsl = "";
            }
        }


        getPreferredCameraId();
        mFocusManager = new FocusManager(mPreferences,
                defaultFocusModes);
        mTouchManager = new TouchManager();


        mIsImageCaptureIntent = isImageCaptureIntent();
        setContentView(R.layout.camera);
        if (mIsImageCaptureIntent) {
            mReviewDoneButton = (Rotatable) findViewById(R.id.btn_done);
            mReviewCancelButton = (Rotatable) findViewById(R.id.btn_cancel);
            findViewById(R.id.btn_cancel).setVisibility(View.VISIBLE);
        } else {
            mThumbnailView = (RotateImageView) findViewById(R.id.thumbnail);
            mThumbnailView.enableFilter(false);
            mThumbnailView.setVisibility(View.VISIBLE);
        }


        mRotateDialog = new RotateDialogController(this, R.layout.rotate_dialog);
        mCaptureLayout = getString(R.string.pref_camera_capture_layout_default);


        mPreferences.setLocalId(this, mCameraId);
        CameraSettings.upgradeLocalPreferences(mPreferences.getLocal());


        mNumberOfCameras = CameraHolder.instance().getNumberOfCameras();
        mQuickCapture = getIntent().getBooleanExtra(EXTRA_QUICK_CAPTURE, false);


        // we need to reset exposure for the preview
        resetExposureCompensation();


        Util.enterLightsOutMode(getWindow());


        // don't set mSurfaceHolder here. We have it set ONLY within
        // surfaceChanged / surfaceDestroyed, other parts of the code
        // assume that when it is set, the surface is also set.
        SurfaceView preview = (SurfaceView) findViewById(R.id.camera_preview);
        SurfaceHolder holder = preview.getHolder();
        holder.addCallback(this);


        s3dView = new S3DViewWrapper(holder);


        holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);


        // Make sure camera device is opened.
        try {
            mCameraOpenThread.join();
            mCameraOpenThread = null;
            if (mOpenCameraFail) {
                Util.showErrorAndFinish(this, R.string.cannot_connect_camera);
                return;
            } else if (mCameraDisabled) {
                Util.showErrorAndFinish(this, R.string.camera_disabled);
                return;
            }
        } catch (InterruptedException ex) {
            // ignore
        }
        mCameraPreviewThread.start();


        if (mIsImageCaptureIntent) {
            setupCaptureParams();
        } else {
            mModePicker = (ModePicker) findViewById(R.id.mode_picker);
            mModePicker.setVisibility(View.VISIBLE);
            mModePicker.setOnModeChangeListener(this);
            mModePicker.setCurrentMode(ModePicker.MODE_CAMERA);
        }


        mZoomControl = (ZoomControl) findViewById(R.id.zoom_control);
        mOnScreenIndicators = (Rotatable) findViewById(R.id.on_screen_indicators);
        mLocationManager = new LocationManager(this, this);


        // Wait until the camera settings are retrieved.
        synchronized (mCameraPreviewThread) {
            try {
                mCameraPreviewThread.wait();
            } catch (InterruptedException ex) {
                // ignore
            }
        }


        // Do this after starting preview because it depends on camera
        // parameters.
        initializeIndicatorControl();
        mCameraSound = new CameraSound();


        // Make sure preview is started.
        try {
            mCameraPreviewThread.join();
        } catch (InterruptedException ex) {
            // ignore
        }
        mCameraPreviewThread = null;
    }
再看看mCameraOpenThread

    Thread mCameraOpenThread = new Thread(new Runnable() {
        public void run() {
            try {
                mCameraDevice = Util.openCamera(Camera.this, mCameraId);
            } catch (CameraHardwareException e) {
                mOpenCameraFail = true;
            } catch (CameraDisabledException e) {
                mCameraDisabled = true;
            }
        }
    });

继续追Util.openCamera ,Util类的定义在以下目录:packages/apps/OMAPCamera/src/com/ti/omap4/android/camera/Util.java
    public static android.hardware.Camera openCamera(Activity activity, int cameraId)
            throws CameraHardwareException, CameraDisabledException {
        // Check if device policy has disabled the camera.
        DevicePolicyManager dpm = (DevicePolicyManager) activity.getSystemService(
                Context.DEVICE_POLICY_SERVICE);
        if (dpm.getCameraDisabled(null)) {
            throw new CameraDisabledException();
        }


        try {
            return CameraHolder.instance().open(cameraId);
        } catch (CameraHardwareException e) {
            // In eng build, we throw the exception so that test tool
            // can detect it and report it
            if ("eng".equals(Build.TYPE)) {
                throw new RuntimeException("openCamera failed", e);
            } else {
                throw e;
            }
        }
    }
又来了个CameraHolder，该类用一个实例openCamera

CameraHolder的定义在以下目录:packages/apps/OMAPCamera/src/com/ti/omap4/android/camera/CameraHolder.java

    public synchronized android.hardware.Camera open(int cameraId)
            throws CameraHardwareException {
        Assert(mUsers == 0);
        if (mCameraDevice != null && mCameraId != cameraId) {
            mCameraDevice.release();
            mCameraDevice = null;
            mCameraId = -1;
        }
        if (mCameraDevice == null) {
            try {
                Log.v(TAG, "open camera " + cameraId);
                mCameraDevice = android.hardware.Camera.open(cameraId);
                mCameraId = cameraId;
            } catch (RuntimeException e) {
                Log.e(TAG, "fail to connect Camera", e);
                throw new CameraHardwareException(e);
            }
            mParameters = mCameraDevice.getParameters();
        } else {
            try {
                mCameraDevice.reconnect();
            } catch (IOException e) {
                Log.e(TAG, "reconnect failed.");
                throw new CameraHardwareException(e);
            }
            mCameraDevice.setParameters(mParameters);
        }
        ++mUsers;
        mHandler.removeMessages(RELEASE_CAMERA);
        mKeepBeforeTime = 0;
        return mCameraDevice;
    }

在这里就开始进入framework层了，调用frameworks\base\core\java\android\hardware\Camera.java类的open方法 。

    public static Camera open(int cameraId) {
        return new Camera(cameraId);
    }
这里调用了Camera的构造函数,在看看构造函数
    Camera(int cameraId) {
        mShutterCallback = null;
        mRawImageCallback = null;
        mJpegCallback = null;
        mPreviewCallback = null;
        mPostviewCallback = null;
        mZoomListener = null;


        Looper looper;
        if ((looper = Looper.myLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else if ((looper = Looper.getMainLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else {
            mEventHandler = null;
        }

        native_setup(new WeakReference<Camera>(this), cameraId);
    }
好，终于来到JNI了

三
继续看camera的JNI文件:frameworks/base/core/jni# gedit android_hardware_Camera.cpp

由于前面Camera的构造函数里调用了native_setup(new WeakReference<Camera>(this), cameraId);

那么native_setup()的定义在那里呢

通过我的查看,在frameworks/base/core/jni# gedit android_hardware_Camera.cpp中有这样一个定义,

我认为通过这个定义,使得native_setup和android_hardware_Camera_native_setup 关联起来

static JNINativeMethod camMethods[] = {
  { "getNumberOfCameras",
    "()I",
    (void *)android_hardware_Camera_getNumberOfCameras },
  { "getCameraInfo",
    "(ILandroid/hardware/Camera$CameraInfo;)V",
    (void*)android_hardware_Camera_getCameraInfo },
  { "native_setup",
    "(Ljava/lang/Object;I)V",
    (void*)android_hardware_Camera_native_setup },
  { "native_release",
    "()V",
    (void*)android_hardware_Camera_release },
  { "setPreviewDisplay",
    "(Landroid/view/Surface;)V",
    (void *)android_hardware_Camera_setPreviewDisplay },
  { "setPreviewTexture",
    "(Landroid/graphics/SurfaceTexture;)V",
    (void *)android_hardware_Camera_setPreviewTexture },
  { "startPreview",
    "()V",
    (void *)android_hardware_Camera_startPreview },
  { "_stopPreview",
    "()V",
    (void *)android_hardware_Camera_stopPreview },
  { "previewEnabled",
    "()Z",
    (void *)android_hardware_Camera_previewEnabled },
  { "setHasPreviewCallback",
    "(ZZ)V",
    (void *)android_hardware_Camera_setHasPreviewCallback },
  { "_addCallbackBuffer",
    "([BI)V",
    (void *)android_hardware_Camera_addCallbackBuffer },
  { "native_autoFocus",
    "()V",
    (void *)android_hardware_Camera_autoFocus },
  { "native_cancelAutoFocus",
    "()V",
    (void *)android_hardware_Camera_cancelAutoFocus },
  { "native_takePicture",
    "(I)V",
    (void *)android_hardware_Camera_takePicture },
  { "native_setParameters",
    "(Ljava/lang/String;)V",
    (void *)android_hardware_Camera_setParameters },
  { "native_getParameters",
    "()Ljava/lang/String;",
    (void *)android_hardware_Camera_getParameters },
  { "reconnect",
    "()V",
    (void*)android_hardware_Camera_reconnect },
  { "lock",
    "()V",
    (void*)android_hardware_Camera_lock },
  { "unlock",
    "()V",
    (void*)android_hardware_Camera_unlock },
  { "startSmoothZoom",
    "(I)V",
    (void *)android_hardware_Camera_startSmoothZoom },
  { "stopSmoothZoom",
    "()V",
    (void *)android_hardware_Camera_stopSmoothZoom },
  { "setDisplayOrientation",
    "(I)V",
    (void *)android_hardware_Camera_setDisplayOrientation },
  { "_startFaceDetection",
    "(I)V",
    (void *)android_hardware_Camera_startFaceDetection },
  { "_stopFaceDetection",
    "()V",
    (void *)android_hardware_Camera_stopFaceDetection},
};

所以,native_setup(new WeakReference<Camera>(this), cameraId);这个调用即是对下面android_hardware_Camera_native_setup这个函数的调用

// connect to camera service
static void android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
    jobject weak_this, jint cameraId)
{
    sp<Camera> camera = Camera::connect(cameraId);

    if (camera == NULL) {
        jniThrowRuntimeException(env, "Fail to connect to camera service");
        return;
    }


    // make sure camera hardware is alive
    if (camera->getStatus() != NO_ERROR) {
        jniThrowRuntimeException(env, "Camera initialization failed");
        return;
    }


    jclass clazz = env->GetObjectClass(thiz);
    if (clazz == NULL) {
        jniThrowRuntimeException(env, "Can't find android/hardware/Camera");
        return;
    }


    // We use a weak reference so the Camera object can be garbage collected.
    // The reference is only used as a proxy for callbacks.
    sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera);
    context->incStrong(thiz);
    camera->setListener(context);


    // save context in opaque field
    env->SetIntField(thiz, fields.context, (int)context.get());
}
JNI函数里面，我们找到Camera C/S架构的客户端了，它调用connect函数向服务器发送连接请求。JNICameraContext这个类是一个监听类，用于处理底层Camera回调函数传来的数据和消息
看看客户端的connect函数有什么,connect定义在以下路径frameworks/base/libs/camera/camera.cpp

sp<Camera> Camera::connect(int cameraId)
{
    LOGV("connect");
    sp<Camera> c = new Camera();
    const sp<ICameraService>& cs = getCameraService();
    if (cs != 0) {
        c->mCamera = cs->connect(c, cameraId);
    }
    if (c->mCamera != 0) {
        c->mCamera->asBinder()->linkToDeath(c);
        c->mStatus = NO_ERROR;
    } else {
        c.clear();
    }
    return c;
}

const sp<ICameraService>& cs =getCameraService();获取CameraService实例。

进入getCameraService（）中

// establish binder interface to camera service
const sp<ICameraService>& Camera::getCameraService()
{
    Mutex::Autolock _l(mLock);
    if (mCameraService.get() == 0) {
        sp<IServiceManager> sm = defaultServiceManager();
        sp<IBinder> binder;
        do {
            binder = sm->getService(String16("media.camera"));
            if (binder != 0)
                break;
            LOGW("CameraService not published, waiting...");
            usleep(500000); // 0.5 s
        } while(true);
        if (mDeathNotifier == NULL) {
            mDeathNotifier = new DeathNotifier();
        }
        binder->linkToDeath(mDeathNotifier);
         mCameraService = interface_cast<ICameraService>(binder);
    }
    LOGE_IF(mCameraService==0, "no CameraService!?");
    return mCameraService;
}
CameraService实例通过binder获取的，mCameraService即为CameraService的实例。
 
回到sp<Camera> Camera::connect(int cameraId)中
c->mCamera = cs->connect(c, cameraId);
即：执行server的connect（）函数，并且返回ICamera对象，赋值给Camera的mCamera，服务端connect（）返回的是他内部类的一个实例。
server的connect（）函数定义在以下路径: frameworks/base/services/camera/libcameraservice/ CameraService.cpp

sp<ICamera> CameraService::connect(
        const sp<ICameraClient>& cameraClient, int cameraId) {
    int callingPid = getCallingPid();
    sp<CameraHardwareInterface> hardware = NULL;


    LOG1("CameraService::connect E (pid %d, id %d)", callingPid, cameraId);


    if (!mModule) {
        LOGE("Camera HAL module not loaded");
        return NULL;
    }


    sp<Client> client;
    if (cameraId < 0 || cameraId >= mNumberOfCameras) {
        LOGE("CameraService::connect X (pid %d) rejected (invalid cameraId %d).",
            callingPid, cameraId);
        return NULL;
    }


    char value[PROPERTY_VALUE_MAX];
    property_get("sys.secpolicy.camera.disabled", value, "0");
    if (strcmp(value, "1") == 0) {
        // Camera is disabled by DevicePolicyManager.
        LOGI("Camera is disabled. connect X (pid %d) rejected", callingPid);
        return NULL;
    }


    Mutex::Autolock lock(mServiceLock);
    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;
            } else {
                LOGW("CameraService::connect X (pid %d) rejected (existing client).",
                    callingPid);
                return NULL;
            }
        }
        mClient[cameraId].clear();
    }


    if (mBusy[cameraId]) {
        LOGW("CameraService::connect X (pid %d) rejected"
             " (camera %d is still busy).", callingPid, cameraId);
        return NULL;
    }


    struct camera_info info;
    if (mModule->get_camera_info(cameraId, &info) != OK) {
        LOGE("Invalid camera id %d", cameraId);
        return NULL;
    }


    char camera_device_name[10];
    snprintf(camera_device_name, sizeof(camera_device_name), "%d", cameraId);


    hardware = new CameraHardwareInterface(camera_device_name);
    if (hardware->initialize(&mModule->common) != OK) {
        hardware.clear();
        return NULL;
    }


    client = new Client(this, cameraClient, hardware, cameraId, info.facing, callingPid);
    mClient[cameraId] = client;
    LOG1("CameraService::connect X");
    return client;
}
实例化Camera Hal接口 hardware，hardware调用initialize()进入HAL层打开Camear驱动。
CameraHardwareInterface中initialize()定义在以下路径:frameworks/base/services/camera/libcameraservice/CameraHardwareInterface.h

代码如下：

    status_t initialize(hw_module_t *module)
    {
        LOGI("Opening camera %s", mName.string());
        int rc = module->methods->open(module, mName.string(),
                                       (hw_device_t **)&mDevice);
        if (rc != OK) {
            LOGE("Could not open camera %s: %d", mName.string(), rc);
            return rc;
        }
#ifdef OMAP_ENHANCEMENT_CPCAM
        initHalPreviewWindow(&mHalPreviewWindow);
        initHalPreviewWindow(&mHalTapin);
        initHalPreviewWindow(&mHalTapout);
#else
        initHalPreviewWindow();
#endif
        return rc;
    }
此处通过module->method->open()方法真正打开Camera设备,

其中module的定义在以下路径:

class CameraService :
    public BinderService<CameraService>,
    public BnCameraService
{

    class Client : public BnCamera
    {
    public:
        ......

    private:

        .....

    };

    camera_module_t *mModule;

};

此处还必须找到camera_module_t 的定义,以更好的理解整个运行流程,通过追根溯源找到了camera_module_t 定义,

camera_module_t的定义在以下路径:hardware/libhardware/include/hardware/camera.h中,定义如下

typedef struct camera_module {
    hw_module_t common;
    int (*get_number_of_cameras)(void);
    int (*get_camera_info)(int camera_id, struct camera_info *info);
} camera_module_t;
其中包含get_number_of_cameras方法和get_camera_info方法用于获取camera info

另外hw_module_t common;这个选项十分重要,此处应重点关注,因为是使用hw_module_t结构体中的open()方法打开设备文件的

继续找到hw_module_t 结构体的定义.在以下路径:hardware/libhardware/include/hardware/hardware.h,代码如下:

struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;


/**
 * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
 * and the fields of this data structure must begin with hw_module_t
 * followed by module specific information.
 */
typedef struct hw_module_t {
    /** tag must be initialized to HARDWARE_MODULE_TAG */
    uint32_t tag;


    /** major version number for the module */
    uint16_t version_major;


    /** minor version number of the module */
    uint16_t version_minor;


    /** Identifier of module */
    const char *id;


    /** Name of this module */
    const char *name;


    /** Author/owner/implementor of the module */
    const char *author;


    /** Modules methods */
    struct hw_module_methods_t* methods;


    /** module's dso */
    void* dso;


    /** padding to 128 bytes, reserved for future use */
    uint32_t reserved[32-7];


} hw_module_t;

同样,找到hw_module_methods_t这个结构体的定义,代码如下:

typedef struct hw_module_methods_t {
    /** Open a specific device */
    int (*open)(const struct hw_module_t* module, const char* id,
            struct hw_device_t** device);
} hw_module_methods_t;

hw_module_methods_t 结构体中只有open()一个方法,用于打开camera driver,实现与硬件层的交互

到此为止,很容易看出:

Android中Camera的调用流程可分为以下几个层次：
Package->Framework->JNI->Camera(cpp)--(binder)-->CameraService->Camera HAL->Camera Driver