Android P Camera2相机简单解析（一、openCamera）

openCamera

CameraManager
文件路径：/frameworks/base/core/java/android/hardware/camera2/CameraManager.java
上层调用的API有两个，分别如下：

@RequiresPermission(android.Manifest.permission.CAMERA) 
public void openCamera(@NonNull String cameraId,
            @NonNull final CameraDevice.StateCallback callback, @Nullable Handler handler)
            throws CameraAccessException {

        openCameraForUid(cameraId, callback, CameraDeviceImpl.checkAndWrapHandler(handler),
                USE_CALLING_UID);
}

@RequiresPermission(android.Manifest.permission.CAMERA)
public void openCamera(@NonNull String cameraId,
            @NonNull @CallbackExecutor Executor executor,
            @NonNull final CameraDevice.StateCallback callback)
            throws CameraAccessException {
        if (executor == null) {
            throw new IllegalArgumentException("executor was null");
        }
        openCameraForUid(cameraId, callback, executor, USE_CALLING_UID);
 }

但是两种实际都是调用了 openCameraForUid(cameraId, callback, executor, USE_CALLING_UID)这个方法，这个方法实际上也是在此文件中，具体实现如下：

public void openCameraForUid(@NonNull String cameraId,
            @NonNull final CameraDevice.StateCallback callback, @NonNull Executor executor,
            int clientUid)
            throws CameraAccessException {

        if (cameraId == null) {
            throw new IllegalArgumentException("cameraId was null");
        } else if (callback == null) {
            throw new IllegalArgumentException("callback was null");
        }
        if (CameraManagerGlobal.sCameraServiceDisabled) {
            throw new IllegalArgumentException("No cameras available on device");
        }

        openCameraDeviceUserAsync(cameraId, callback, executor, clientUid);
    }

这里做了容错性判断，紧接着调用了 openCameraDeviceUserAsync(cameraId, callback, executor, clientUid)，此方法也是在当前文件中，实现如下：

private CameraDevice openCameraDeviceUserAsync(String cameraId,
            CameraDevice.StateCallback callback, Executor executor, final int uid)
            throws CameraAccessException {
        CameraCharacteristics characteristics = getCameraCharacteristics(cameraId);
        CameraDevice device = null;

        synchronized (mLock) {

            ICameraDeviceUser cameraUser = null;

            android.hardware.camera2.impl.CameraDeviceImpl deviceImpl =
                    new android.hardware.camera2.impl.CameraDeviceImpl(
                        cameraId,
                        callback,
                        executor,
                        characteristics,
                        mContext.getApplicationInfo().targetSdkVersion);

            ICameraDeviceCallbacks callbacks = deviceImpl.getCallbacks();

            try {
                if (supportsCamera2ApiLocked(cameraId)) {
                    // Use cameraservice's cameradeviceclient implementation for HAL3.2+ devices
                    ICameraService cameraService = CameraManagerGlobal.get().getCameraService();
                    if (cameraService == null) {
                        throw new ServiceSpecificException(
                            ICameraService.ERROR_DISCONNECTED,
                            "Camera service is currently unavailable");
                    }
                    cameraUser = cameraService.connectDevice(callbacks, cameraId,
                            mContext.getOpPackageName(), uid);
                } else {
                    // Use legacy camera implementation for HAL1 devices
                    int id;
                    try {
                        id = Integer.parseInt(cameraId);
                    } catch (NumberFormatException e) {
                        throw new IllegalArgumentException("Expected cameraId to be numeric, but it was: "
                                + cameraId);
                    }

                    Log.i(TAG, "Using legacy camera HAL.");
                    cameraUser = CameraDeviceUserShim.connectBinderShim(callbacks, id);
                }
            } catch (ServiceSpecificException e) {
                if (e.errorCode == ICameraService.ERROR_DEPRECATED_HAL) {
                    throw new AssertionError("Should've gone down the shim path");
                } else if (e.errorCode == ICameraService.ERROR_CAMERA_IN_USE ||
                        e.errorCode == ICameraService.ERROR_MAX_CAMERAS_IN_USE ||
                        e.errorCode == ICameraService.ERROR_DISABLED ||
                        e.errorCode == ICameraService.ERROR_DISCONNECTED ||
                        e.errorCode == ICameraService.ERROR_INVALID_OPERATION) {
                    // Received one of the known connection errors
                    // The remote camera device cannot be connected to, so
                    // set the local camera to the startup error state
                    deviceImpl.setRemoteFailure(e);

                    if (e.errorCode == ICameraService.ERROR_DISABLED ||
                            e.errorCode == ICameraService.ERROR_DISCONNECTED ||
                            e.errorCode == ICameraService.ERROR_CAMERA_IN_USE) {
                        // Per API docs, these failures call onError and throw
                        throwAsPublicException(e);
                    }
                } else {
                    // Unexpected failure - rethrow
                    throwAsPublicException(e);
                }
            } catch (RemoteException e) {
                // Camera service died - act as if it's a CAMERA_DISCONNECTED case
                ServiceSpecificException sse = new ServiceSpecificException(
                    ICameraService.ERROR_DISCONNECTED,
                    "Camera service is currently unavailable");
                deviceImpl.setRemoteFailure(sse);
                throwAsPublicException(sse);
            }

            // TODO: factor out callback to be non-nested, then move setter to constructor
            // For now, calling setRemoteDevice will fire initial
            // onOpened/onUnconfigured callbacks.
            // This function call may post onDisconnected and throw CAMERA_DISCONNECTED if
            // cameraUser dies during setup.
            deviceImpl.setRemoteDevice(cameraUser);
            device = deviceImpl;
        }

        return device;
    }

这里主要关注上面的代码不仅仅23-31行中的cameraService.connectDevice，这仅仅是Connect到我们的Camera设备，并不能打开我们的Camera，所以第9行的ICameraDeviceUser cameraUser = null和第82行的deviceImpl.setRemoteDevice(cameraUser)也是非常重要的，这里对应了CameraDeviceImpl .java文件。但是这里我们还是先看cameraService.connectDevice实现，实际上是ICameraService.connectDevice，这里需要注意的是ICameraService实际上是aidl文件，也是就是说CameraManager通过通过 Binder 机制调用了 connectDevice 方法，这个connectDevice方法的实现在CameraService 中。
CameraService
文件路径：/frameworks/av/services/camera/libcameraservice/CameraService.cpp
代码如下：

Status CameraService::connectDevice(
        const sp<hardware::camera2::ICameraDeviceCallbacks>& cameraCb,
        const String16& cameraId,
        const String16& clientPackageName,
        int clientUid,
        /*out*/
        sp<hardware::camera2::ICameraDeviceUser>* device) {

    ATRACE_CALL();
    Status ret = Status::ok();
    String8 id = String8(cameraId);
    sp<CameraDeviceClient> client = nullptr;
    ret = connectHelper<hardware::camera2::ICameraDeviceCallbacks,CameraDeviceClient>(cameraCb, id,
            /*api1CameraId*/-1,
            CAMERA_HAL_API_VERSION_UNSPECIFIED, clientPackageName,
            clientUid, USE_CALLING_PID, API_2,
            /*legacyMode*/ false, /*shimUpdateOnly*/ false,
            /*out*/client);

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

    *device = client;
    return ret;
}

不难发现这里第13行调用了connectHelper来实现连接相机的逻辑，具体代码如下：

Status CameraService::connectHelper(const sp<CALLBACK>& cameraCb, const String8& cameraId,
        int api1CameraId, int halVersion, const String16& clientPackageName, int clientUid,
        int clientPid, apiLevel effectiveApiLevel, bool legacyMode, bool shimUpdateOnly,
        /*out*/sp<CLIENT>& device) {
    binder::Status ret = binder::Status::ok();

    String8 clientName8(clientPackageName);

    int originalClientPid = 0;

    ALOGI("CameraService::connect call (PID %d \"%s\", camera ID %s) for HAL version %s and "
            "Camera API version %d", clientPid, clientName8.string(), cameraId.string(),
            (halVersion == -1) ? "default" : std::to_string(halVersion).c_str(),
            static_cast<int>(effectiveApiLevel));

    sp<CLIENT> client = nullptr;
    {
        // Acquire mServiceLock and prevent other clients from connecting
        std::unique_ptr<AutoConditionLock> lock =
                AutoConditionLock::waitAndAcquire(mServiceLockWrapper, DEFAULT_CONNECT_TIMEOUT_NS);

        if (lock == nullptr) {
            ALOGE("CameraService::connect (PID %d) rejected (too many other clients connecting)."
                    , clientPid);
            return STATUS_ERROR_FMT(ERROR_MAX_CAMERAS_IN_USE,
                    "Cannot open camera %s for \"%s\" (PID %d): Too many other clients connecting",
                    cameraId.string(), clientName8.string(), clientPid);
        }

        // Enforce client permissions and do basic sanity checks
        if(!(ret = validateConnectLocked(cameraId, clientName8,
                /*inout*/clientUid, /*inout*/clientPid, /*out*/originalClientPid)).isOk()) {
            return ret;
        }

        // Check the shim parameters after acquiring lock, if they have already been updated and
        // we were doing a shim update, return immediately
        if (shimUpdateOnly) {
            auto cameraState = getCameraState(cameraId);
            if (cameraState != nullptr) {
                if (!cameraState->getShimParams().isEmpty()) return ret;
            }
        }

        status_t err;

        sp<BasicClient> clientTmp = nullptr;
        std::shared_ptr<resource_policy::ClientDescriptor<String8, sp<BasicClient>>> partial;
        if ((err = handleEvictionsLocked(cameraId, originalClientPid, effectiveApiLevel,
                IInterface::asBinder(cameraCb), clientName8, /*out*/&clientTmp,
                /*out*/&partial)) != NO_ERROR) {
            switch (err) {
                case -ENODEV:
                    return STATUS_ERROR_FMT(ERROR_DISCONNECTED,
                            "No camera device with ID \"%s\" currently available",
                            cameraId.string());
                case -EBUSY:
                    return STATUS_ERROR_FMT(ERROR_CAMERA_IN_USE,
                            "Higher-priority client using camera, ID \"%s\" currently unavailable",
                            cameraId.string());
                default:
                    return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                            "Unexpected error %s (%d) opening camera \"%s\"",
                            strerror(-err), err, cameraId.string());
            }
        }

        if (clientTmp.get() != nullptr) {
            // Handle special case for API1 MediaRecorder where the existing client is returned
            device = static_cast<CLIENT*>(clientTmp.get());
            return ret;
        }

        // give flashlight a chance to close devices if necessary.
        mFlashlight->prepareDeviceOpen(cameraId);

        int facing = -1;
        int deviceVersion = getDeviceVersion(cameraId, /*out*/&facing);
        if (facing == -1) {
            ALOGE("%s: Unable to get camera device \"%s\"  facing", __FUNCTION__, cameraId.string());
            return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                    "Unable to get camera device \"%s\" facing", cameraId.string());
        }

        sp<BasicClient> tmp = nullptr;
        if(!(ret = makeClient(this, cameraCb, clientPackageName,
                cameraId, api1CameraId, 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, mMonitorTags);
        if (err != OK) {
            ALOGE("%s: Could not initialize client from HAL.", __FUNCTION__);
            // Errors could be from the HAL module open call or from AppOpsManager
            switch(err) {
                case BAD_VALUE:
                    return STATUS_ERROR_FMT(ERROR_ILLEGAL_ARGUMENT,
                            "Illegal argument to HAL module for camera \"%s\"", cameraId.string());
                case -EBUSY:
                    return STATUS_ERROR_FMT(ERROR_CAMERA_IN_USE,
                            "Camera \"%s\" is already open", cameraId.string());
                case -EUSERS:
                    return STATUS_ERROR_FMT(ERROR_MAX_CAMERAS_IN_USE,
                            "Too many cameras already open, cannot open camera \"%s\"",
                            cameraId.string());
                case PERMISSION_DENIED:
                    return STATUS_ERROR_FMT(ERROR_PERMISSION_DENIED,
                            "No permission to open camera \"%s\"", cameraId.string());
                case -EACCES:
                    return STATUS_ERROR_FMT(ERROR_DISABLED,
                            "Camera \"%s\" disabled by policy", cameraId.string());
                case -ENODEV:
                default:
                    return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                            "Failed to initialize camera \"%s\": %s (%d)", cameraId.string(),
                            strerror(-err), err);
            }
        }

        // Update shim paremeters for legacy clients
        if (effectiveApiLevel == API_1) {
            // Assume we have always received a Client subclass for API1
            sp<Client> shimClient = reinterpret_cast<Client*>(client.get());
            String8 rawParams = shimClient->getParameters();
            CameraParameters params(rawParams);

            auto cameraState = getCameraState(cameraId);
            if (cameraState != nullptr) {
                cameraState->setShimParams(params);
            } else {
                ALOGE("%s: Cannot update shim parameters for camera %s, no such device exists.",
                        __FUNCTION__, cameraId.string());
            }
        }

        if (shimUpdateOnly) {
            // If only updating legacy shim parameters, immediately disconnect client
            mServiceLock.unlock();
            client->disconnect();
            mServiceLock.lock();
        } else {
            // Otherwise, add client to active clients list
            finishConnectLocked(client, partial);
        }
    } // lock is destroyed, allow further connect calls

    // Important: release the mutex here so the client can call back into the service from its
    // destructor (can be at the end of the call)
    device = client;
    return ret;
}

在connectHelper中我们通过makeClient方法完成了client的生成并初始化，具体实现如下：

Status CameraService::makeClient(const sp<CameraService>& cameraService,
        const sp<IInterface>& cameraCb, const String16& packageName, const String8& cameraId,
        int api1CameraId, 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 CameraClient
        // based on device version reported by the HAL.
        switch(deviceVersion) {
          case CAMERA_DEVICE_API_VERSION_1_0:
            if (effectiveApiLevel == API_1) {  // Camera1 API route
                sp<ICameraClient> tmp = static_cast<ICameraClient*>(cameraCb.get());
                *client = new CameraClient(cameraService, tmp, packageName,
                        api1CameraId, facing, clientPid, clientUid,
                        getpid(), legacyMode);
            } else { // Camera2 API route
                ALOGW("Camera using old HAL version: %d", deviceVersion);
                return STATUS_ERROR_FMT(ERROR_DEPRECATED_HAL,
                        "Camera device \"%s\" HAL version %d does not support camera2 API",
                        cameraId.string(), deviceVersion);
            }
            break;
          case CAMERA_DEVICE_API_VERSION_3_0:
          case CAMERA_DEVICE_API_VERSION_3_1:
          case CAMERA_DEVICE_API_VERSION_3_2:
          case CAMERA_DEVICE_API_VERSION_3_3:
          case CAMERA_DEVICE_API_VERSION_3_4:
            if (effectiveApiLevel == API_1) { // Camera1 API route
                sp<ICameraClient> tmp = static_cast<ICameraClient*>(cameraCb.get());
                *client = new Camera2Client(cameraService, tmp, packageName,
                        cameraId, api1CameraId,
                        facing, clientPid, clientUid,
                        servicePid, legacyMode);
            } else { // Camera2 API route
                sp<hardware::camera2::ICameraDeviceCallbacks> tmp =
                        static_cast<hardware::camera2::ICameraDeviceCallbacks*>(cameraCb.get());
                *client = new CameraDeviceClient(cameraService, tmp, packageName, cameraId,
                        facing, clientPid, clientUid, servicePid);
            }
            break;
          default:
            // Should not be reachable
            ALOGE("Unknown camera device HAL version: %d", deviceVersion);
            return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                    "Camera device \"%s\" has unknown HAL version %d",
                    cameraId.string(), deviceVersion);
        }
    } else {
        // A particular HAL version is requested by caller. Create CameraClient
        // based on the requested HAL version.
        if (deviceVersion > CAMERA_DEVICE_API_VERSION_1_0 &&
            halVersion == CAMERA_DEVICE_API_VERSION_1_0) {
            // Only support higher HAL version device opened as HAL1.0 device.
            sp<ICameraClient> tmp = static_cast<ICameraClient*>(cameraCb.get());
            *client = new CameraClient(cameraService, tmp, packageName,
                    api1CameraId, facing, clientPid, clientUid,
                    servicePid, legacyMode);
        } else {
            // Other combinations (e.g. HAL3.x open as HAL2.x) are not supported yet.
            ALOGE("Invalid camera HAL version %x: HAL %x device can only be"
                    " opened as HAL %x device", halVersion, deviceVersion,
                    CAMERA_DEVICE_API_VERSION_1_0);
            return STATUS_ERROR_FMT(ERROR_ILLEGAL_ARGUMENT,
                    "Camera device \"%s\" (HAL version %d) cannot be opened as HAL version %d",
                    cameraId.string(), deviceVersion, halVersion);
        }
    }
    return Status::ok();
}

这一块儿基本就是根据API版本和Device版本来实例化Client的，在Android P 和Camera2的框架上，这里需要跟进的是38-39行，这里CameraDeviceClient方法是由CameraDeviceClient.cpp实现的。
CameraDeviceClient.cpp
文件路径：/frameworks/av/services/camera/libcameraservice/api2/CameraDeviceClient.cpp

CameraDeviceClient::CameraDeviceClient(const sp<CameraService>& cameraService,
        const sp<hardware::camera2::ICameraDeviceCallbacks>& remoteCallback,
        const String16& clientPackageName,
        const String8& cameraId,
        int cameraFacing,
        int clientPid,
        uid_t clientUid,
        int servicePid) :
    Camera2ClientBase(cameraService, remoteCallback, clientPackageName,
                cameraId, /*API1 camera ID*/ -1,
                cameraFacing, clientPid, clientUid, servicePid),
    mInputStream(),
    mStreamingRequestId(REQUEST_ID_NONE),
    mRequestIdCounter(0) {

    ATRACE_CALL();
    ALOGI("CameraDeviceClient %s: Opened", cameraId.string());
}

这里关注第9行，发现又调用了Camera2ClientBase方法，实现代码如下：

Camera2ClientBase<TClientBase>::Camera2ClientBase(
        const sp<CameraService>& cameraService,
        const sp<TCamCallbacks>& remoteCallback,
        const String16& clientPackageName,
        const String8& cameraId,
        int api1CameraId,
        int cameraFacing,
        int clientPid,
        uid_t clientUid,
        int servicePid):
        TClientBase(cameraService, remoteCallback, clientPackageName,
                cameraId, api1CameraId, cameraFacing, clientPid, clientUid, servicePid),
        mSharedCameraCallbacks(remoteCallback),
        mDeviceVersion(cameraService->getDeviceVersion(TClientBase::mCameraIdStr)),
        mDeviceActive(false), mApi1CameraId(api1CameraId)
{
    ALOGI("Camera %s: Opened. Client: %s (PID %d, UID %d)", cameraId.string(),
            String8(clientPackageName).string(), clientPid, clientUid);

    mInitialClientPid = clientPid;
    mDevice = new Camera3Device(cameraId);
    LOG_ALWAYS_FATAL_IF(mDevice == 0, "Device should never be NULL here.");
}

好吧，第21行mDevice = new Camera3Device(cameraId)才是重点，是由Camera3Device.cpp实现的。
Camera3Device.cpp
文件路径：/frameworks/av/services/camera/libcameraservice/device3/Camera3Device.cpp

Camera3Device::Camera3Device(const String8 &id):
        mId(id),
        mOperatingMode(NO_MODE),
        mIsConstrainedHighSpeedConfiguration(false),
        mStatus(STATUS_UNINITIALIZED),
        mStatusWaiters(0),
        mUsePartialResult(false),
        mNumPartialResults(1),
        mTimestampOffset(0),
        mNextResultFrameNumber(0),
        mNextReprocessResultFrameNumber(0),
        mNextShutterFrameNumber(0),
        mNextReprocessShutterFrameNumber(0),
        mListener(NULL),
        mVendorTagId(CAMERA_METADATA_INVALID_VENDOR_ID),
        mLastTemplateId(-1)
{
    ATRACE_CALL();
    camera3_callback_ops::notify = &sNotify;
    camera3_callback_ops::process_capture_result = &sProcessCaptureResult;
    ALOGV("%s: Created device for camera %s", __FUNCTION__, mId.string());
}

到此CameraService.cpp中的makeClient工作就已经完成了并构造了"CameraDeviceClient"，接下来就是connectHelper中的client->initialize这块儿了，从上面分析我们知道这里的client 指的对象就是Camera3Device了，所以我们继续找到Camera3Device中的initialize方法，代码如下：

status_t Camera3Device::initialize(sp<CameraProviderManager> manager, const String8& monitorTags) {
    ATRACE_CALL();
    Mutex::Autolock il(mInterfaceLock);
    Mutex::Autolock l(mLock);

    ALOGV("%s: Initializing HIDL device for camera %s", __FUNCTION__, mId.string());
    if (mStatus != STATUS_UNINITIALIZED) {
        CLOGE("Already initialized!");
        return INVALID_OPERATION;
    }
    if (manager == nullptr) return INVALID_OPERATION;

    sp<ICameraDeviceSession> session;
    ATRACE_BEGIN("CameraHal::openSession");
    status_t res = manager->openSession(mId.string(), this,
            /*out*/ &session);
    ATRACE_END();
    if (res != OK) {
        SET_ERR_L("Could not open camera session: %s (%d)", strerror(-res), res);
        return res;
    }

    res = manager->getCameraCharacteristics(mId.string(), &mDeviceInfo);
    if (res != OK) {
        SET_ERR_L("Could not retrive camera characteristics: %s (%d)", strerror(-res), res);
        session->close();
        return res;
    }

    std::shared_ptr<RequestMetadataQueue> queue;
    auto requestQueueRet = session->getCaptureRequestMetadataQueue(
        [&queue](const auto& descriptor) {
            queue = std::make_shared<RequestMetadataQueue>(descriptor);
            if (!queue->isValid() || queue->availableToWrite() <= 0) {
                ALOGE("HAL returns empty request metadata fmq, not use it");
                queue = nullptr;
                // don't use the queue onwards.
            }
        });
    if (!requestQueueRet.isOk()) {
        ALOGE("Transaction error when getting request metadata fmq: %s, not use it",
                requestQueueRet.description().c_str());
        return DEAD_OBJECT;
    }

    std::unique_ptr<ResultMetadataQueue>& resQueue = mResultMetadataQueue;
    auto resultQueueRet = session->getCaptureResultMetadataQueue(
        [&resQueue](const auto& descriptor) {
            resQueue = std::make_unique<ResultMetadataQueue>(descriptor);
            if (!resQueue->isValid() || resQueue->availableToWrite() <= 0) {
                ALOGE("HAL returns empty result metadata fmq, not use it");
                resQueue = nullptr;
                // Don't use the resQueue onwards.
            }
        });
    if (!resultQueueRet.isOk()) {
        ALOGE("Transaction error when getting result metadata queue from camera session: %s",
                resultQueueRet.description().c_str());
        return DEAD_OBJECT;
    }
    IF_ALOGV() {
        session->interfaceChain([](
            ::android::hardware::hidl_vec<::android::hardware::hidl_string> interfaceChain) {
                ALOGV("Session interface chain:");
                for (auto iface : interfaceChain) {
                    ALOGV("  %s", iface.c_str());
                }
            });
    }

    mInterface = new HalInterface(session, queue); //新建硬件抽象层接口实例
    std::string providerType;
    mVendorTagId = manager->getProviderTagIdLocked(mId.string());
    mTagMonitor.initialize(mVendorTagId);
    if (!monitorTags.isEmpty()) {
        mTagMonitor.parseTagsToMonitor(String8(monitorTags));
    }

    return initializeCommonLocked();
}

代码中第15行 res = manager->openSession 就是走向open的地方了，但是还是需要继续到一个方法，不难发现openSession方法由CameraProviderManager.cpp实现。此外在这里我们还需要注意第31和47行，第31行是请求队列，47行是结果队列在下一篇中将使用到。

CameraProviderManager.cpp
文件路径：***/frameworks/av/services/camera/libcameraservice/common/CameraProviderManager.cpp***
具体代码如下：

status_t CameraProviderManager::openSession(const std::string &id,
        const sp<hardware::camera::device::V3_2::ICameraDeviceCallback>& callback,
        /*out*/
        sp<hardware::camera::device::V3_2::ICameraDeviceSession> *session) {

    std::lock_guard<std::mutex> lock(mInterfaceMutex);

    auto deviceInfo = findDeviceInfoLocked(id,
            /*minVersion*/ {3,0}, /*maxVersion*/ {4,0});
    if (deviceInfo == nullptr) return NAME_NOT_FOUND;

    auto *deviceInfo3 = static_cast<ProviderInfo::DeviceInfo3*>(deviceInfo);

    Status status;
    hardware::Return<void> ret;
    ret = deviceInfo3->mInterface->open(callback, [&status, &session]
            (Status s, const sp<device::V3_2::ICameraDeviceSession>& cameraSession) {
                status = s;
                if (status == Status::OK) {
                    *session = cameraSession;
                }
            });
    if (!ret.isOk()) {
        ALOGE("%s: Transaction error opening a session for camera device %s: %s",
                __FUNCTION__, id.c_str(), ret.description().c_str());
        return DEAD_OBJECT;
    }
    return mapToStatusT(status);
}

其中第16行ret = deviceInfo3->mInterface->open 实际上通过Hidl指向了CameraDevice::open()，该方法由CameraDevice.cpp实现。

CameraDevice.cpp
文件路径：***/hardware/interfaces/camera/device/3.2/default/CameraDevice.cpp***
代码如下：

Return<void> CameraDevice::open(const sp<ICameraDeviceCallback>& callback, open_cb _hidl_cb)  {
    Status status = initStatus();
    sp<CameraDeviceSession> session = nullptr;

    if (callback == nullptr) {
        ALOGE("%s: cannot open camera %s. callback is null!",
                __FUNCTION__, mCameraId.c_str());
        _hidl_cb(Status::ILLEGAL_ARGUMENT, nullptr);
        return Void();
    }

    if (status != Status::OK) {
        // Provider will never pass initFailed device to client, so
        // this must be a disconnected camera
        ALOGE("%s: cannot open camera %s. camera is disconnected!",
                __FUNCTION__, mCameraId.c_str());
        _hidl_cb(Status::CAMERA_DISCONNECTED, nullptr);
        return Void();
    } else {
        mLock.lock();

        ALOGV("%s: Initializing device for camera %d", __FUNCTION__, mCameraIdInt);
        session = mSession.promote();
        if (session != nullptr && !session->isClosed()) {
            ALOGE("%s: cannot open an already opened camera!", __FUNCTION__);
            mLock.unlock();
            _hidl_cb(Status::CAMERA_IN_USE, nullptr);
            return Void();
        }

        /** Open HAL device */
        status_t res;
        camera3_device_t *device;

        ATRACE_BEGIN("camera3->open");
        res = mModule->open(mCameraId.c_str(),
                reinterpret_cast<hw_device_t**>(&device));
        ATRACE_END();

        if (res != OK) {
            ALOGE("%s: cannot open camera %s!", __FUNCTION__, mCameraId.c_str());
            mLock.unlock();
            _hidl_cb(getHidlStatus(res), nullptr);
            return Void();
        }

        /** Cross-check device version */
        if (device->common.version < CAMERA_DEVICE_API_VERSION_3_2) {
            ALOGE("%s: Could not open camera: "
                    "Camera device should be at least %x, reports %x instead",
                    __FUNCTION__,
                    CAMERA_DEVICE_API_VERSION_3_2,
                    device->common.version);
            device->common.close(&device->common);
            mLock.unlock();
            _hidl_cb(Status::ILLEGAL_ARGUMENT, nullptr);
            return Void();
        }

        struct camera_info info;
        res = mModule->getCameraInfo(mCameraIdInt, &info);
        if (res != OK) {
            ALOGE("%s: Could not open camera: getCameraInfo failed", __FUNCTION__);
            device->common.close(&device->common);
            mLock.unlock();
            _hidl_cb(Status::ILLEGAL_ARGUMENT, nullptr);
            return Void();
        }

        session = createSession(
                device, info.static_camera_characteristics, callback);
        if (session == nullptr) {
            ALOGE("%s: camera device session allocation failed", __FUNCTION__);
            mLock.unlock();
            _hidl_cb(Status::INTERNAL_ERROR, nullptr);
            return Void();
        }
        if (session->isInitFailed()) {
            ALOGE("%s: camera device session init failed", __FUNCTION__);
            session = nullptr;
            mLock.unlock();
            _hidl_cb(Status::INTERNAL_ERROR, nullptr);
            return Void();
        }
        mSession = session;

        IF_ALOGV() {
            session->getInterface()->interfaceChain([](
                ::android::hardware::hidl_vec<::android::hardware::hidl_string> interfaceChain) {
                    ALOGV("Session interface chain:");
                    for (auto iface : interfaceChain) {
                        ALOGV("  %s", iface.c_str());
                    }
                });
        }
        mLock.unlock();
    }
    _hidl_cb(status, session->getInterface());
    return Void();
}

其中36-37行的res = mModule->open(mCameraId.c_str(), reinterpret_cast<hw_device_t**>(&device))为打开Camera的地方，但是这里还需要继续跟下去，指向了CameraModule.cpp中实现的open方法。

CameraModule.cpp
文件路径：***/hardware/interfaces/camera/common/1.0/default/CameraModule.cpp***
代码如下：

int CameraModule::open(const char* id, struct hw_device_t** device) {
    int res;
    ATRACE_BEGIN("camera_module->open");
    res = filterOpenErrorCode(mModule->common.methods->open(&mModule->common, id, device));
    ATRACE_END();
    return res;
}

不难发现，mModule->common.methods->open紧接着就是Hal层了，在这里我们需要先把Hal层启动流程弄清楚。在系统启动后，CameraService服务跑起来就是就会启动Hal层。
CameraService
文件路径：***/frameworks/av/services/camera/libcameraservice/CameraService.cpp***
代码如下：

void CameraService::onFirstRef()
{
    ALOGI("CameraService process starting");

    BnCameraService::onFirstRef();

    // Update battery life tracking if service is restarting
    BatteryNotifier& notifier(BatteryNotifier::getInstance());
    notifier.noteResetCamera();
    notifier.noteResetFlashlight();

    status_t res = INVALID_OPERATION;

    res = enumerateProviders();
    if (res == OK) {
        mInitialized = true;
    }

    CameraService::pingCameraServiceProxy();

    mUidPolicy = new UidPolicy(this);
    mUidPolicy->registerSelf();
}

这里第14行res = enumerateProviders()说明CameraService在初始化时，要先枚举Provider，实现代码如下：

status_t CameraService::enumerateProviders() {
    status_t res;

    std::vector<std::string> deviceIds;
    {
        Mutex::Autolock l(mServiceLock);

        if (nullptr == mCameraProviderManager.get()) {
            mCameraProviderManager = new CameraProviderManager();
            res = mCameraProviderManager->initialize(this);
            if (res != OK) {
                ALOGE("%s: Unable to initialize camera provider manager: %s (%d)",
                        __FUNCTION__, strerror(-res), res);
                return res;
            }
        }


        // Setup vendor tags before we call get_camera_info the first time
        // because HAL might need to setup static vendor keys in get_camera_info
        // TODO: maybe put this into CameraProviderManager::initialize()?
        mCameraProviderManager->setUpVendorTags();

        if (nullptr == mFlashlight.get()) {
            mFlashlight = new CameraFlashlight(mCameraProviderManager, this);
        }

        res = mFlashlight->findFlashUnits();
        if (res != OK) {
            ALOGE("Failed to enumerate flash units: %s (%d)", strerror(-res), res);
        }

        deviceIds = mCameraProviderManager->getCameraDeviceIds();
    }


    for (auto& cameraId : deviceIds) {
        String8 id8 = String8(cameraId.c_str());
        onDeviceStatusChanged(id8, CameraDeviceStatus::PRESENT);
    }

    return OK;
}

这里又先初始化CameraProviderManager，并获取第三方厂家TAG，获取闪光灯，获取相机设备数，其中CameraProviderManager的初始化实现如下。
CameraProviderManager.cpp
文件路径：***/frameworks/av/services/camera/libcameraservice/common/CameraProviderManager.cpp***
具体代码如下：

status_t CameraProviderManager::initialize(wp<CameraProviderManager::StatusListener> listener,
        ServiceInteractionProxy* proxy) {
    std::lock_guard<std::mutex> lock(mInterfaceMutex);
    if (proxy == nullptr) {
        ALOGE("%s: No valid service interaction proxy provided", __FUNCTION__);
        return BAD_VALUE;
    }
    mListener = listener;
    mServiceProxy = proxy;

    // Registering will trigger notifications for all already-known providers
    bool success = mServiceProxy->registerForNotifications(
        /* instance name, empty means no filter */ "",
        this);
    if (!success) {
        ALOGE("%s: Unable to register with hardware service manager for notifications "
                "about camera providers", __FUNCTION__);
        return INVALID_OPERATION;
    }

    // See if there's a passthrough HAL, but let's not complain if there's not
    addProviderLocked(kLegacyProviderName, /*expected*/ false);
    addProviderLocked(kExternalProviderName, /*expected*/ false);

    return OK;
}

CameraProviderManager初始化中做的事情很明了，这里我们需要关注的是addProviderLocked这里进行查找并保存Provider，实现如下：

status_t CameraProviderManager::addProviderLocked(const std::string& newProvider, bool expected) {
    for (const auto& providerInfo : mProviders) {
        if (providerInfo->mProviderName == newProvider) {
            ALOGW("%s: Camera provider HAL with name '%s' already registered", __FUNCTION__,
                    newProvider.c_str());
            return ALREADY_EXISTS;
        }
    }

    sp<provider::V2_4::ICameraProvider> interface;
    interface = mServiceProxy->getService(newProvider); //获取服务

    if (interface == nullptr) {
        if (expected) {
            ALOGE("%s: Camera provider HAL '%s' is not actually available", __FUNCTION__,
                    newProvider.c_str());
            return BAD_VALUE;
        } else {
            return OK;
        }
    }

    sp<ProviderInfo> providerInfo =
            new ProviderInfo(newProvider, interface, this); //构建
    status_t res = providerInfo->initialize(); //初始化
    if (res != OK) {
        return res;
    }

    mProviders.push_back(providerInfo); //备份

    return OK;
}

这里需要关注 spprovider::V2_4::ICameraProvider interface这里的interface，最终指向了CameraProvider.cpp,不过我们需要先关注上面的构建和初始化providerInfo->initialize()，代码如下：

status_t CameraProviderManager::ProviderInfo::initialize() {
    status_t res = parseProviderName(mProviderName, &mType, &mId);
    if (res != OK) {
        ALOGE("%s: Invalid provider name, ignoring", __FUNCTION__);
        return BAD_VALUE;
    }
    ALOGI("Connecting to new camera provider: %s, isRemote? %d",
            mProviderName.c_str(), mInterface->isRemote());
    // cameraDeviceStatusChange callbacks may be called (and causing new devices added)
    // before setCallback returns
    hardware::Return<Status> status = mInterface->setCallback(this);
    if (!status.isOk()) {
        ALOGE("%s: Transaction error setting up callbacks with camera provider '%s': %s",
                __FUNCTION__, mProviderName.c_str(), status.description().c_str());
        return DEAD_OBJECT;
    }
    if (status != Status::OK) {
        ALOGE("%s: Unable to register callbacks with camera provider '%s'",
                __FUNCTION__, mProviderName.c_str());
        return mapToStatusT(status);
    }

    hardware::Return<bool> linked = mInterface->linkToDeath(this, /*cookie*/ mId);
    if (!linked.isOk()) {
        ALOGE("%s: Transaction error in linking to camera provider '%s' death: %s",
                __FUNCTION__, mProviderName.c_str(), linked.description().c_str());
        return DEAD_OBJECT;
    } else if (!linked) {
        ALOGW("%s: Unable to link to provider '%s' death notifications",
                __FUNCTION__, mProviderName.c_str());
    }

    // Get initial list of camera devices, if any
    std::vector<std::string> devices;
    hardware::Return<void> ret = mInterface->getCameraIdList([&status, &devices](
            Status idStatus,
            const hardware::hidl_vec<hardware::hidl_string>& cameraDeviceNames) {
        status = idStatus;
        if (status == Status::OK) {
            for (size_t i = 0; i < cameraDeviceNames.size(); i++) {
                devices.push_back(cameraDeviceNames[i]);
            }
        } });
    if (!ret.isOk()) {
        ALOGE("%s: Transaction error in getting camera ID list from provider '%s': %s",
                __FUNCTION__, mProviderName.c_str(), linked.description().c_str());
        return DEAD_OBJECT;
    }
    if (status != Status::OK) {
        ALOGE("%s: Unable to query for camera devices from provider '%s'",
                __FUNCTION__, mProviderName.c_str());
        return mapToStatusT(status);
    }

    sp<StatusListener> listener = mManager->getStatusListener();
    for (auto& device : devices) {
        std::string id;
        status_t res = addDevice(device,
                hardware::camera::common::V1_0::CameraDeviceStatus::PRESENT, &id);//添加device
        if (res != OK) {
            ALOGE("%s: Unable to enumerate camera device '%s': %s (%d)",
                    __FUNCTION__, device.c_str(), strerror(-res), res);
            continue;
        }
    }

    ALOGI("Camera provider %s ready with %zu camera devices",
            mProviderName.c_str(), mDevices.size());

    mInitialized = true;
    return OK;
}

这里主要关注上面的添加设备这块儿

status_t CameraProviderManager::ProviderInfo::addDevice(const std::string& name,
        CameraDeviceStatus initialStatus, /*out*/ std::string* parsedId) {

    ALOGI("Enumerating new camera device: %s", name.c_str());

    uint16_t major, minor;
    std::string type, id;

    status_t res = parseDeviceName(name, &major, &minor, &type, &id);
    if (res != OK) {
        return res;
    }
    if (type != mType) {
        ALOGE("%s: Device type %s does not match provider type %s", __FUNCTION__,
                type.c_str(), mType.c_str());
        return BAD_VALUE;
    }
    if (mManager->isValidDeviceLocked(id, major)) {
        ALOGE("%s: Device %s: ID %s is already in use for device major version %d", __FUNCTION__,
                name.c_str(), id.c_str(), major);
        return BAD_VALUE;
    }

    std::unique_ptr<DeviceInfo> deviceInfo;
    switch (major) {
    	//实例化
        case 1:
            deviceInfo = initializeDeviceInfo<DeviceInfo1>(name, mProviderTagid,
                    id, minor);
            break;
        case 3:
            deviceInfo = initializeDeviceInfo<DeviceInfo3>(name, mProviderTagid,
                    id, minor);
            break;
        default:
            ALOGE("%s: Device %s: Unknown HIDL device HAL major version %d:", __FUNCTION__,
                    name.c_str(), major);
            return BAD_VALUE;
    }
    if (deviceInfo == nullptr) return BAD_VALUE;
    deviceInfo->mStatus = initialStatus;
    bool isAPI1Compatible = deviceInfo->isAPI1Compatible();

    mDevices.push_back(std::move(deviceInfo));

    mUniqueCameraIds.insert(id);
    if (isAPI1Compatible) {
        mUniqueAPI1CompatibleCameraIds.push_back(id);
    }

    if (parsedId != nullptr) {
        *parsedId = id;
    }
    return OK;
}

其中实例化device代码如下：

template<class DeviceInfoT>
std::unique_ptr<CameraProviderManager::ProviderInfo::DeviceInfo>
    CameraProviderManager::ProviderInfo::initializeDeviceInfo(
        const std::string &name, const metadata_vendor_id_t tagId,
        const std::string &id, uint16_t minorVersion) const {
    Status status;

    auto cameraInterface =
            getDeviceInterface<typename DeviceInfoT::InterfaceT>(name); //获取HAL层远程接口
    if (cameraInterface == nullptr) return nullptr;

    CameraResourceCost resourceCost;
    cameraInterface->getResourceCost([&status, &resourceCost](
        Status s, CameraResourceCost cost) {
                status = s;
                resourceCost = cost;
            });
    if (status != Status::OK) {
        ALOGE("%s: Unable to obtain resource costs for camera device %s: %s", __FUNCTION__,
                name.c_str(), statusToString(status));
        return nullptr;
    }

    for (auto& conflictName : resourceCost.conflictingDevices) {
        uint16_t major, minor;
        std::string type, id;
        status_t res = parseDeviceName(conflictName, &major, &minor, &type, &id);
        if (res != OK) {
            ALOGE("%s: Failed to parse conflicting device %s", __FUNCTION__, conflictName.c_str());
            return nullptr;
        }
        conflictName = id;
    }

    return std::unique_ptr<DeviceInfo>(
        new DeviceInfoT(name, tagId, id, minorVersion, resourceCost,
                cameraInterface));
}

其中获取HAL远程接口代码如下：

template<>
sp<device::V3_2::ICameraDevice>
CameraProviderManager::ProviderInfo::getDeviceInterface
        <device::V3_2::ICameraDevice>(const std::string &name) const {
    Status status;
    sp<device::V3_2::ICameraDevice> cameraInterface;
    hardware::Return<void> ret;
    ret = mInterface->getCameraDeviceInterface_V3_x(name, [&status, &cameraInterface](
        Status s, sp<device::V3_2::ICameraDevice> interface) {
                status = s;
                cameraInterface = interface;
            });
    if (!ret.isOk()) {
        ALOGE("%s: Transaction error trying to obtain interface for camera device %s: %s",
                __FUNCTION__, name.c_str(), ret.description().c_str());
        return nullptr;
    }
    if (status != Status::OK) {
        ALOGE("%s: Unable to obtain interface for camera device %s: %s", __FUNCTION__,
                name.c_str(), statusToString(status));
        return nullptr;
    }
    return cameraInterface;
}

到了这里，可以看出ICameraDevice关联到了CameraDevice.cpp，那么providerInfo->initialize()就分析得差不多了，下面的就到了硬件层，回头来我们需要继续分析CameraProvider.cpp这里了，在这里就关注其初始化就可以了。
CameraProvider.cpp
文件路径：***/hardware/interfaces/camera/provider/2.4/default/CameraProvider.cpp***
代码如下：

bool CameraProvider::initialize() {
    camera_module_t *rawModule;
    int err = hw_get_module(CAMERA_HARDWARE_MODULE_ID,
            (const hw_module_t **)&rawModule);
    if (err < 0) {
        ALOGE("Could not load camera HAL module: %d (%s)", err, strerror(-err));
        return true;
    }

    mModule = new CameraModule(rawModule);
    err = mModule->init();
    if (err != OK) {
        ALOGE("Could not initialize camera HAL module: %d (%s)", err, strerror(-err));
        mModule.clear();
        return true;
    }
    ALOGI("Loaded \"%s\" camera module", mModule->getModuleName());

    // Setup vendor tags here so HAL can setup vendor keys in camera characteristics
    VendorTagDescriptor::clearGlobalVendorTagDescriptor();
    if (!setUpVendorTags()) {
        ALOGE("%s: Vendor tag setup failed, will not be available.", __FUNCTION__);
    }

    // Setup callback now because we are going to try openLegacy next
    err = mModule->setCallbacks(this);
    if (err != OK) {
        ALOGE("Could not set camera module callback: %d (%s)", err, strerror(-err));
        mModule.clear();
        return true;
    }

    mPreferredHal3MinorVersion =
        property_get_int32("ro.vendor.camera.wrapper.hal3TrebleMinorVersion", 3);
    ALOGV("Preferred HAL 3 minor version is %d", mPreferredHal3MinorVersion);
    switch(mPreferredHal3MinorVersion) {
        case 2:
        case 3:
            // OK
            break;
        default:
            ALOGW("Unknown minor camera device HAL version %d in property "
                    "'camera.wrapper.hal3TrebleMinorVersion', defaulting to 3",
                    mPreferredHal3MinorVersion);
            mPreferredHal3MinorVersion = 3;
    }

    mNumberOfLegacyCameras = mModule->getNumberOfCameras();
    for (int i = 0; i < mNumberOfLegacyCameras; i++) {
        struct camera_info info;
        auto rc = mModule->getCameraInfo(i, &info);
        if (rc != NO_ERROR) {
            ALOGE("%s: Camera info query failed!", __func__);
            mModule.clear();
            return true;
        }

        if (checkCameraVersion(i, info) != OK) {
            ALOGE("%s: Camera version check failed!", __func__);
            mModule.clear();
            return true;
        }

        char cameraId[kMaxCameraIdLen];
        snprintf(cameraId, sizeof(cameraId), "%d", i);
        std::string cameraIdStr(cameraId);
        mCameraStatusMap[cameraIdStr] = CAMERA_DEVICE_STATUS_PRESENT;

        addDeviceNames(i);
    }

    return false; // mInitFailed
}

这里就初始化了CameraMoudle。