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));
   &nbs

补充：移动开发 , Android ,