android camera jni调用

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how to compile library of native camera for android ndk? http://stackoverflow.com/questions/22859299/how-to-use-library-of-native-camera-for-android-ndk

Android Camera 采用C/S架构，client 与server两个独立的线程之间（CameraService）使用Binder通信。

一 CameraService的注册。

1.手机开机后，会走init.rc流程，init.rc会启动MediaServer Service。

service media /system/bin/mediaserver

    class main

    user root ####

#   google default ####

#   user media    ####

    group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm media sdcard_r system net_bt_stack ####

#   google default ####

#   group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm ####

    ioprio rt 4

2.MediaServer的main函数位于frameworks/base/media/mediaserver/main_mediaserver.cpp中。

在Main_MediaServer.cpp的main函数中，CameraService完成了注册

 1 int main(int argc __unused, char** argv)

 2 {

 3     signal(SIGPIPE, SIG_IGN);

 4     char value[PROPERTY_VALUE_MAX];

 5     bool doLog = (property_get("ro.test_harness", value, "0") > 0) && (atoi(value) == 1);

 6     pid_t childPid;

 7 ..............................

 8         sp<ProcessState> proc(ProcessState::self());

 9         sp<IServiceManager> sm = defaultServiceManager();

10         ALOGI("ServiceManager: %p", sm.get());

11         AudioFlinger::instantiate();

12         MediaPlayerService::instantiate();

13 #ifdef MTK_AOSP_ENHANCEMENT

14         MemoryDumper::instantiate();

15 #endif

16         CameraService::instantiate();

17 ......................................

3. instantiate的实现在CameraService的父类中，

namespace android {

template<typename SERVICE>

class BinderService

{

public:

    static status_t publish(bool allowIsolated = false) {

        sp<IServiceManager> sm(defaultServiceManager());

        return sm->addService(

                String16(SERVICE::getServiceName()),

                new SERVICE(), allowIsolated);

    }

    static void publishAndJoinThreadPool(bool allowIsolated = false) {

        publish(allowIsolated);

        joinThreadPool();

    }

    static void instantiate() { publish(); }

    static status_t shutdown() { return NO_ERROR; }

private:

    static void joinThreadPool() {

        sp<ProcessState> ps(ProcessState::self());

        ps->startThreadPool();

        ps->giveThreadPoolName();

        IPCThreadState::self()->joinThreadPool();

    }

};

}; // namespace android

可以发现在publish(）函数中，CameraService完成服务的注册。SERVICE是个模板，这里是注册CameraService，所以可用CameraService代替

return sm->addService(String16(CameraService::getServiceName()), new CameraService());

这样，Camera就在ServiceManager完成服务注册，提供给client随时使用。

二 client如何连上server端，并打开camera模块

我们从Camera.open()开始往framework进行分析，调用frameworks\base\core\java\android\hardware\Camera.java类的open方法。

public static Camera open() {

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

    return new Camera(cameraId);

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

}

这里调用了Camera的构造函数,在构造函数中调用了cameraInitVersion

    private int cameraInitVersion(int cameraId, int halVersion) {

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

        return native_setup(new WeakReference<Camera>(this), cameraId, halVersion, packageName);

    }

此后进入JNI层android_hardware_camera.cpp

// connect to camera service

static jint android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,

    jobject weak_this, jint cameraId, jint halVersion, jstring clientPackageName)

{

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

        camera = Camera::connect(cameraId, clientName,

                Camera::USE_CALLING_UID);

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

    sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera);

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

    camera->setListener(context);

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

}

JNI函数里面，我们找到Camera C/S架构的客户端了（即红色加粗的那个Camera），它调用connect函数向服务端发送连接请求。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

sp<Camera> Camera::connect(int cameraId, const String16& clientPackageName,

        int clientUid)

{

    return CameraBaseT::connect(cameraId, clientPackageName, clientUid);

}

template <typename TCam, typename TCamTraits>

sp<TCam> CameraBase<TCam, TCamTraits>::connect(int cameraId,

                                               const String16& clientPackageName,

                                               int clientUid)

{

    ALOGV("%s: connect", __FUNCTION__);

    sp<TCam> c = new TCam(cameraId);

    sp<TCamCallbacks> cl = c;

    status_t status = NO_ERROR;

    const sp<ICameraService>& cs = getCameraService();

    if (cs != 0) {

        TCamConnectService fnConnectService = TCamTraits::fnConnectService;

        status = (cs.get()->*fnConnectService)(cl, cameraId, clientPackageName, clientUid,

                                             /*out*/ c->mCamera);

    }

    if (status == OK && c->mCamera != 0) {

        c->mCamera->asBinder()->linkToDeath(c);

        c->mStatus = NO_ERROR;

    } else {

        ALOGW("An error occurred while connecting to camera: %d", cameraId);

        c.clear();

    }

    return c;

}

// establish binder interface to camera service

template <typename TCam, typename TCamTraits>

const sp<ICameraService>& CameraBase<TCam, TCamTraits>::getCameraService()

{

    Mutex::Autolock _l(gLock);

    if (gCameraService.get() == 0) {

        sp<IServiceManager> sm = defaultServiceManager();

        sp<IBinder> binder;

        do {

            binder = sm->getService(String16(kCameraServiceName));

            if (binder != 0) {

                break;

            }

            ALOGW("CameraService not published, waiting...");

            usleep(kCameraServicePollDelay);

        } while(true);

        if (gDeathNotifier == NULL) {

            gDeathNotifier = new DeathNotifier();

        }

        binder->linkToDeath(gDeathNotifier);

        gCameraService = interface_cast<ICameraService>(binder);

    }

    ALOGE_IF(gCameraService == 0, "no CameraService!?");

    return gCameraService;

}

此处终于获得CameraService实例了，该CameraService实例是通过binder获取的。

再来看fnConnectService是什么，

在Camera.cpp中，有

CameraTraits<Camera>::TCamConnectService CameraTraits<Camera>::fnConnectService =

        &ICameraService::connect;

这样也就是说fnConnectService就是使用CameraService调用connect，从这里开始，终于从进入了服务端的流程：

status_t CameraService::connect(

        const sp<ICameraClient>& cameraClient,

        int cameraId,

        const String16& clientPackageName,

        int clientUid,

        /*out*/

        sp<ICamera>& device) {

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

    status_t status = validateConnect(cameraId, /*inout*/clientUid);

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

if (!canConnectUnsafe(cameraId, clientPackageName,

                              cameraClient->asBinder(),

                              /*out*/clientTmp)) {

            return -EBUSY;

        } 

        status = connectHelperLocked(/*out*/client,

                                     cameraClient,

                                     cameraId,

                                     clientPackageName,

                                     clientUid,

                                     callingPid);

return OK;

}

status_t CameraService::connectHelperLocked(

        /*out*/

        sp<Client>& client,

        /*in*/

        const sp<ICameraClient>& cameraClient,

        int cameraId,

        const String16& clientPackageName,

        int clientUid,

        int callingPid,

        int halVersion,

        bool legacyMode) {

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

            client = new CameraClient(this, cameraClient,

                    clientPackageName, cameraId,

                    facing, callingPid, clientUid, getpid(), legacyMode);

....................................       
    status_t status = connectFinishUnsafe(client, client->getRemote());
............................................

}

在connectHelpLocked，CameraService返回一个其实是它内部类的client——CameraClient。（注意此client是CameraService内部的CameraClient，不是Camera客户端）

在connectFinishUnsafe中，

    status_t status = client->initialize(mModule);

我们再来看CameraClient类的initialize函数

status_t CameraClient::initialize(camera_module_t *module) {

    int callingPid = getCallingPid();

    status_t res;

    mHardware = new CameraHardwareInterface(camera_device_name);

    res = mHardware->initialize(&module->common);

}

CameraClient的初始化就是：先实例化Camera Hal接口 CameraHardwareInterface，CameraHardwareInterface调用initialize()进入HAL层打开Camera底层驱动

    status_t initialize(hw_module_t *module)

    {

        ALOGI("Opening camera %s", mName.string());

        camera_module_t *cameraModule = reinterpret_cast<camera_module_t *>(module);

        camera_info info;

        status_t res = cameraModule->get_camera_info(atoi(mName.string()), &info);

        if (res != OK) return res;

        int rc = OK;

        if (module->module_api_version >= CAMERA_MODULE_API_VERSION_2_3 &&

            info.device_version > CAMERA_DEVICE_API_VERSION_1_0) {

            // Open higher version camera device as HAL1.0 device.

            rc = cameraModule->open_legacy(module, mName.string(),

                                               CAMERA_DEVICE_API_VERSION_1_0,

                                               (hw_device_t **)&mDevice);

        } else {

            rc = CameraService::filterOpenErrorCode(module->methods->open(

                module, mName.string(), (hw_device_t **)&mDevice));

        }

        if (rc != OK) {

            ALOGE("Could not open camera %s: %d", mName.string(), rc);

            return rc;

        }

        initHalPreviewWindow();

        return rc;

    }

hardware->initialize(&mModule->common)中mModule模块是一个结构体camera_module_t，他是怎么初始化的呢？我们发现CameraService里面有个函数

void CameraService::onFirstRef()

{

    BnCameraService::onFirstRef();

    if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,

                (const hw_module_t **)&mModule) < 0) {

        LOGE("Could not load camera HAL module");

        mNumberOfCameras = 0;

    }

}

了解HAL层的都知道hw_get_module函数就是用来获取模块的Hal stub，这里通过CAMERA_HARDWARE_MODULE_ID 获取Camera Hal层的代理stub，并赋值给mModule，后面就可通过操作mModule完成对Camera模块的控制。那么onFirstRef()函数又是何时调用的？

onFirstRef（）属于其父类RefBase，该函数在强引用sp新增引用计数时调用。就是当有sp包装的类初始化的时候调用，那么camera是何时调用的呢？可以发现在

客户端发起连接时候

sp Camera::connect(int cameraId)
{
    LOGV("connect");
    sp c = new Camera();
    const sp& cs = getCameraService();

}

这个时候初始化了一个CameraService实例，且用Sp包装，这个时候sp将新增计数，相应的CameraService实例里面onFirstRef（）函数完成调用。
CameraService::connect（）即实例化CameraClient并打开驱动，返回CameraClient的时候，就表明客户端和服务端连接建立。Camera完成初始化。

参考文档：

Android 4.0 Camera架构分析之Camera初始化 http://blog.csdn.net/dnfchan/article/details/7594590

Android 5.1 Camera Framework源码