Android Camera1 open流程分析

 

由于camera 1网上大家分析的文章比较多，这里就截取各处细节在做继续深究.

前段部分流程可以看：Android Camera 流程学习记录（二）—— Camera Open 调用流程，这里分析CameraService.cpp以下部分.

1.C/C++ 层:

1.1 CameraService.cp

• 位置：frameworks/av/services/camera/libcameraservice/CameraService.cpp
• connect()： 
  • 注意这里真正实现逻辑是在 connectHelper() 函数中。
  • 获得一个客户端实例并且通过 *device 返回。

上面分析得知，Java 层中会通过 binder 跨进程调用 CameraService::connect(), camera2 会调用到CameraService::connectDevice()，注意里面connectHelper的参数API_1, camera2会对应API_2,

​
Status CameraService::connect(
        const sp<ICameraClient>& cameraClient,
        int cameraId,
        const String16& clientPackageName,
        int clientUid,
        int clientPid,
        /*out*/
        sp<ICamera>* device) {

    ATRACE_CALL();
    Status ret = Status::ok();
    String8 id = String8::format("%d", cameraId);
    sp<Client> client = nullptr;
    ret = connectHelper<ICameraClient,Client>(cameraClient, id,
            CAMERA_HAL_API_VERSION_UNSPECIFIED, clientPackageName, clientUid, clientPid, API_1,
            /*legacyMode*/ false, /*shimUpdateOnly*/ false,
            /*out*/client);

    if(!ret.isOk()) {
        logRejected(id, getCallingPid(), String8(clientPackageName),
                ret.toString8());
        return ret;
    }

    *device = client;
    return ret;
}

​

CameraService.h

位置：frameworks/av/services/camera/libcameraservice/CameraService.h
注意这个文件中定义了 CameraService::Client 类，这个类通过它的子类 CameraClient 真正实现了 ICamera 的接口。

connectHelper()： 

• HAL1 /HAL2 最终也都调用到这个方法
• 这个函数实现比较长，截取其中的一段。
• 首先，如果客户端实例已经存在于 MediaRecorder ，则直接将其取出返回。
• 若不存在，则先获取 deviceVersion，然后再调用 makeClient() 函数创建一个客户端。
• 创建客户端后，需要调用其 initialize() 函数进行初始化，注意其传入的参数是 mModule，这个参数是连接 Libraries 与 HAL 的关键参数。

template<class CALLBACK, class CLIENT>
Status CameraService::connectHelper(const sp<CALLBACK>& cameraCb, const String8& cameraId,
        int halVersion, const String16& clientPackageName, int clientUid, int clientPid,
        apiLevel effectiveApiLevel, bool legacyMode, bool shimUpdateOnly,
        /*out*/sp<CLIENT>& device) {
        ...
        sp<BasicClient> tmp = nullptr;
        ALOGE("%s halVersion = %d , deviceVersion = %d ", __FUNCTION__, halVersion, deviceVersion);
        /* makeClient() 很重要， 后面分析 */
        if(!(ret = makeClient(this, cameraCb, clientPackageName, cameraId, facing, clientPid,
                clientUid, getpid(), legacyMode, halVersion, deviceVersion, effectiveApiLevel,
                /*out*/&tmp)).isOk()) {
            return ret;
        }
        client = static_cast<CLIENT*>(tmp.get());

        LOG_ALWAYS_FATAL_IF(client.get() == nullptr, "%s: CameraService in invalid state",
                __FUNCTION__);

        err = client->initialize(mCameraProviderManager);
       
        ...
        device = client;
    return ret;
}

makeClent:

Status CameraService::makeClient(const sp<CameraService>& cameraService,
        const sp<IInterface>& cameraCb, const String16& packageName, const String8& cameraId,
        int facing, int clientPid, uid_t clientUid, int servicePid, bool legacyMode,
        int halVersion, int deviceVersion, apiLevel effectiveApiLevel,
        /*out*/sp<BasicClient>* client) {
        ...
        if (halVersion < 0 || halVersion == deviceVersion) {
        // Default path: HAL version is unspecified by caller, create Came