Android Camera HAL3中预览preview模式下的控制流

Camera3研读前沿：

    当初在研读Camera1.0相关的内容时，主要围绕着CameraClient、CameraHardwareInterface等方面进行工作的开展，无论是数据流还是控制流看起来都很简单、明了，一系列的流程化操作使得整个框架学起来特别的容易。因为没有Camera2.0相关的基础，所以这次直接看3.0相关的源码时，显得十分的吃紧，再加上底层高通HAL3.0实现的过程也是相当的复杂，都给整个研读过程带来了很多的困难。可以说，自身目前对Camera3.0框架的熟悉度也大概只有70%左右，希望通过总结来进一步梳理他的工作原理与整个框架，并进一步熟悉与加深理解。

1.Camera3下的整体架构图。

整个CameraService建立起一个可用操作底层Camera device大致需要经过Camera2Client、Camera3Device以及HAL层的camera3_device_t三个部分。

从上图中可以发现Camera3架构看上去明显比camera1来的复杂，但他更加的模块化。对比起Android4.2.2 Camer系统架构图（HAL和回调处理）一文中描述的单顺序执行流程，Camera3将更多的工作集中在了Framework去完成，将更多的控制权掌握在自己的手里，从而与HAL的交互的数据信息更少，也进一步减轻了一些在旧版本中HAL层所需要做的事情。

2. Camera2Client的建立与初始化过程

在建立好Camera2Client后会进行initialize操作，完成各个处理模块的创建：

  ....
StreamingProcessor = new StreamingProcessor(this);//preview和recorder
   threadName = String8::format("C2-%d-StreamProc",
           mCameraId);
   mStreamingProcessor->run(threadName.string());//预览与录像

   mFrameProcessor = new FrameProcessor(mDevice, this);// 3A
   threadName = String8::format("C2-%d-FrameProc",
           mCameraId);
   mFrameProcessor->run(threadName.string()); //3A

   mCaptureSequencer = new CaptureSequencer(this);
   threadName = String8::format("C2-%d-CaptureSeq",
           mCameraId);
   mCaptureSequencer->run(threadName.string());//录像，拍照

   mJpegProcessor = new JpegProcessor(this, mCaptureSequencer);
   threadName = String8::format("C2-%d-JpegProc",
           mCameraId);
   mJpegProcessor->run(threadName.string());
...
mCallbackProcessor = new CallbackProcessor(this);//回调处理
   threadName = String8::format("C2-%d-CallbkProc",
           mCameraId);
   mCallbackProcessor->run(threadName.string());

依次分别创建了：

StreamingProcessor并启动一个他所属的thread，该模块主要负责处理previews与record两种视频流的处理，用于从hal层获取原始的视频数据

FrameProcessor并启动一个thread，该模块专门用于处理回调回来的每一帧的3A等信息，即每一帧视频除去原始视频数据外，还应该有其他附加的数据信息，如3A值。

CaptureSequencer并启动一个thread，该模块需要和其他模块配合使用，主要用于向APP层告知capture到的picture。
JpegProcessor并启动一个thread，该模块和streamprocessor类似，他启动一个拍照流，一般用于从HAL层获取jpeg编码后的图像照片数据。

此外ZslProcessor模块称之为0秒快拍，其本质是直接从原始的Preview流中获取预存着的最近的几帧，直接编码后返回给APP，而不需要再经过take picture去请求获取jpeg数据。0秒快拍技术得意于当下处理器CSI2 MIPI性能的提升以及Sensor支持全像素高帧率的实时输出。一般手机拍照在按下快门后都会有一定的延时，是因为需要切换底层Camera以及ISP等的工作模式，并重新设置参数以及重新对焦等等，都需要花一定时间后才抓取一帧用于编码为jpeg图像。

以上5个模块整合在一起基本上实现了Camera应用开发所需的基本业务功能。

3. 预览Preview下的控制流

研读Camera具体的业务处理功能，一般从视频实时预览Preview入手。一般熟悉Camera架构的人，可以从一个app端的一个api一直连续打通到底层hal的一个控制命令。大致可以如下图所示：

对于preview部分到CameraService的控制流可以参考博文Android4.2.2的preview的数据流和控制流以及最终的预览显示，本文将直接从Camera2Client::startPreview() 作为入口来分析整个Framework层中Preview相关的数据流。

status_t Camera2Client::startPreview() {
    ATRACE_CALL();
    ALOGV("%s: E", __FUNCTION__);
    Mutex::Autolock icl(mBinderSerializationLock);
    status_t res;
    if ( (res = checkPid(__FUNCTION__) ) != OK) return res;
    SharedParameters::Lock l(mParameters);
    return startPreviewL(l.mParameters, false);
}

startPreview通过startPreviewL提取参数后真正的开始执行Preview相关的控制流。该函数看上去内容虽然较多，但基本采用了同一种处理方式：

status_t Camera2Client::startPreviewL(Parameters ¶ms, bool restart) {//restart == false
    ATRACE_CALL();
    status_t res;
......
   int lastPreviewStreamId = mStreamingProcessor->getPreviewStreamId();//获取上一层Preview stream id

   res = mStreamingProcessor->updatePreviewStream(params);//创建camera3device stream， Camera3OutputStream
.....
   int lastJpegStreamId = mJpegProcessor->getStreamId();
   res = updateProcessorStream(mJpegProcessor, params);//预览启动时就建立一个jpeg的outstream
.....
        res = mCallbackProcessor->updateStream(params);//回调处理建立一个Camera3outputstream
        if (res != OK) {
            ALOGE("%s: Camera %d: Unable to update callback stream: %s (%d)",
                    __FUNCTION__, mCameraId, strerror(-res), res);
            return res;
        }
        outputStreams.push(getCallbackStreamId());
......
    outputStreams.push(getPreviewStreamId());//预览stream
......
   if (!params.recordingHint) {
        if (!restart) {
            res = mStreamingProcessor->updatePreviewRequest(params);//request处理,更新了mPreviewrequest
            if (res != OK) {
                ALOGE("%s: Camera %d: Can't set up preview request: "
                        "%s (%d)", __FUNCTION__, mCameraId,
                        strerror(-res), res);
                return res;
            }
        }
        res = mStreamingProcessor->startStream(StreamingProcessor::PREVIEW,
                outputStreams);//启动stream，传入outputStreams即stream 的id
    } else {
        if (!restart) {
            res = mStreamingProcessor->updateRecordingRequest(params);
            if (res != OK) {
                ALOGE("%s: Camera %d: Can't set up preview request with "
                        "record hint: %s (%d)", __FUNCTION__, mCameraId,
                        strerror(-res), res);
                return res;
            }
        }
        res = mStreamingProcessor->startStream(StreamingProcessor::RECORD,
                outputStreams);
    }
......
}

(1). mStreamingProcessor->updatePreviewStream()

由预览与录像处理模块更新一个预览流，其实现过程如下：

status_t StreamingProcessor::updatePreviewStream(const Parameters ¶ms) {
    ATRACE_CALL();
    Mutex::Autolock m(mMutex);

    status_t res;
    sp device = mDevice.promote();//Camera3Device
    if (device == 0) {
        ALOGE("%s: Camera %d: Device does not exist", __FUNCTION__, mId);
        return INVALID_OPERATION;
    }

    if (mPreviewStreamId != NO_STREAM) {
        // Check if stream parameters have to change
        uint32_t currentWidth, currentHeight;
        res = device->getStreamInfo(mPreviewStreamId,
                ¤tWidth, ¤tHeight, 0);
        if (res != OK) {
            ALOGE("%s: Camera %d: Error querying preview stream info: "
                    "%s (%d)", __FUNCTION__, mId, strerror(-res), res);
            return res;
        }
        if (currentWidth != (uint32_t)params.previewWidth ||
                currentHeight != (uint32_t)params.previewHeight) {
            ALOGV("%s: Camera %d: Preview size switch: %d x %d -> %d x %d",
                    __FUNCTION__, mId, currentWidth, currentHeight,
                    params.previewWidth, params.previewHeight);
            res = device->waitUntilDrained();
            if (res != OK) {
                ALOGE("%s: Camera %d: Error waiting for preview to drain: "
                        "%s (%d)", __FUNCTION__, mId, strerror(-res), res);
                return res;
            }
            res = device->deleteStream(mPreviewStreamId);
            if (res != OK) {
                ALOGE("%s: Camera %d: Unable to delete old output stream "
                        "for preview: %s (%d)", __FUNCTION__, mId,
                        strerror(-res), res);
                return res;
            }
            mPreviewStreamId = NO_STREAM;
        }
    }

    if (mPreviewStreamId == NO_STREAM) {//首次create stream
        res = device->createStream(mPreviewWindow,
                params.previewWidth, params.previewHeight,
                CAMERA2_HAL_PIXEL_FORMAT_OPAQUE, &mPreviewStreamId);//创建一个Camera3OutputStream
        if (res != OK) {
            ALOGE("%s: Camera %d: Unable to create preview stream: %s (%d)",
                    __FUNCTION__, mId, strerror(-res), res);
            return res;
        }
    }

    res = device->setStreamTransform(mPreviewStreamId,
            params.previewTransform);
    if (res != OK) {
        ALOGE("%s: Camera %d: Unable to set preview stream transform: "
                "%s (%d)", __FUNCTION__, mId, strerror(-res), res);
        return res;
    }

    return OK;
}

该函数首先是查看当前 StreamingProcessor模块下是否存在Stream，没有的话，则交由Camera3Device创建一个stream。显然，一个StreamingProcessor只能拥有一个PreviewStream，而一个Camera3Device显然控制着所有的Stream。

注意：在Camera2Client中，Stream大行其道，5大模块的数据交互均以stream作为基础。

下面我们来重点关注Camera3Device的接口createStream，他是5个模块创建stream的基础：

status_t Camera3Device::createStream(sp consumer,
        uint32_t width, uint32_t height, int format, int *id) {
    ATRACE_CALL();
    Mutex::Autolock il(mInterfaceLock);
    Mutex::Autolock l(mLock);
    ALOGV("Camera %d: Creating new stream %d: %d x %d, format %d",
            mId, mNextStreamId, width, height, format);

    status_t res;
    bool wasActive = false;

    switch (mStatus) {
        case STATUS_ERROR:
            CLOGE("Device has encountered a serious error");
            return INVALID_OPERATION;
        case STATUS_UNINITIALIZED:
            CLOGE("Device not initialized");
            return INVALID_OPERATION;
        case STATUS_UNCONFIGURED:
        case STATUS_CONFIGURED:
            // OK
            break;
        case STATUS_ACTIVE:
            ALOGV("%s: Stopping activity to reconfigure streams", __FUNCTION__);
            res = internalPauseAndWaitLocked();
            if (res != OK) {
                SET_ERR_L("Can't pause captures to reconfigure streams!");
                return res;
            }
            wasActive = true;
            break;
        default:
            SET_ERR_L("Unexpected status: %d", mStatus);
            return INVALID_OPERATION;
    }
    assert(mStatus != STATUS_ACTIVE);

    sp newStream;
    if (format == HAL_PIXEL_FORMAT_BLOB) {//图片
        ssize_t jpegBufferSize = getJpegBufferSize(width, height);
        if (jpegBufferSize <= 0) {
            SET_ERR_L("Invalid jpeg buffer size %zd", jpegBufferSize);
            return BAD_VALUE;
        }

        newStream = new Camera3OutputStream(mNextStreamId, consumer,
                width, height, jpegBufferSize, format);//jpeg 缓存的大小
    } else {
        newStream = new Camera3OutputStream(mNextStreamId, consumer,
                width, height, format);//Camera3OutputStream
    }
    newStream->setStatusTracker(mStatusTracker);

    res = mOutputStreams.add(mNextStreamId, newStream);//一个streamid与Camera3OutputStream绑定
    if (res < 0) {
        SET_ERR_L("Can't add new stream to set: %s (%d)", strerror(-res), res);
        return res;
    }

    *id = mNextStreamId++;//至少一个previewstream 一般还有CallbackStream
    mNeedConfig = true;

    // Continue captures if active at start
    if (wasActive) {
        ALOGV("%s: Restarting activity to reconfigure streams", __FUNCTION__);
        res = configureStreamsLocked();
        if (res != OK) {
            CLOGE("Can't reconfigure device for new stream %d: %s (%d)",
                    mNextStreamId, strerror(-res), res);
            return res;
        }
        internalResumeLocked();
    }
    ALOGV("Camera %d: Created new stream", mId);
    return OK;
}

该函数重点是关注一个new Camera3OutputStream，在Camera3Device主要存在 Camera3OutputStream和Camera3InputStream
两种stream，前者主要作为HAL的输出，是请求HAL填充数据的OutPutStream，后者是由Framework将Stream进行填充。无论是Preview、record还是capture均是从HAL层获取数据，故都会以OutPutStream的形式存在，是我们关注的重点，后面在描述Preview的数据流时还会进一步的阐述。

每当创建一个OutPutStream后，相关的stream信息被push维护在一个mOutputStreams的KeyedVector >表中，分别是该stream在Camera3Device中创建时的ID以及Camera3OutputStream的sp值。同时对mNextStreamId记录下一个Stream的ID号。

上述过程完成StreamingProcessor模块中一个PreviewStream的创建，其中Camera3OutputStream创建时的ID值被返回记录作为mPreviewStreamId的值，此外每个Stream都会有一个对应的ANativeWindow，这里称之为Consumer。

（2）mCallbackProcessor->updateStream(params)

对比StreamingProcessor模块创建previewstream的过程，很容易定位到Callback模块是需要建立一个callback流，同样需要创建一个Camera3OutputStream来接收HAL返回的每一帧帧数据，是否需要callback可以通过callbackenable来控制。一般但预览阶段可能不需要回调每一帧的数据到APP，但涉及到相应的其他业务如视频处理时，就需要进行callback的enable。

status_t CallbackProcessor::updateStream(const Parameters ¶ms) {
    ATRACE_CALL();
    status_t res;

    Mutex::Autolock l(mInputMutex);

    sp device = mDevice.promote();
    if (device == 0) {
        ALOGE("%s: Camera %d: Device does not exist", __FUNCTION__, mId);
        return INVALID_OPERATION;
    }

    // If possible, use the flexible YUV format
    int32_t callbackFormat = params.previewFormat;
    if (mCallbackToApp) {
        // TODO: etalvala: This should use the flexible YUV format as well, but
        // need to reconcile HAL2/HAL3 requirements.
        callbackFormat = HAL_PIXEL_FORMAT_YV12;
    } else if(params.fastInfo.useFlexibleYuv &&
            (params.previewFormat == HAL_PIXEL_FORMAT_YCrCb_420_SP ||
             params.previewFormat == HAL_PIXEL_FORMAT_YV12) ) {
        callbackFormat = HAL_PIXEL_FORMAT_YCbCr_420_888;
    }

    if (!mCallbackToApp && mCallbackConsumer == 0) {
        // Create CPU buffer queue endpoint, since app hasn't given us one
        // Make it async to avoid disconnect deadlocks
        sp producer;
        sp consumer;
        BufferQueue::createBufferQueue(&producer, &consumer);//BufferQueueProducer与BufferQueueConsumer
        mCallbackConsumer = new CpuConsumer(consumer, kCallbackHeapCount);
        mCallbackConsumer->setFrameAvailableListener(this);//当前CallbackProcessor继承于CpuConsumer::FrameAvailableListener
        mCallbackConsumer->setName(String8("Camera2Client::CallbackConsumer"));
        mCallbackWindow = new Surface(producer);//用于queue操作，这里直接进行本地的buffer操作
    }

    if (mCallbackStreamId != NO_STREAM) {
        // Check if stream parameters have to change
        uint32_t currentWidth, currentHeight, currentFormat;
        res = device->getStreamInfo(mCallbackStreamId,
                ¤tWidth, ¤tHeight, ¤tFormat);
        if (res != OK) {
            ALOGE("%s: Camera %d: Error querying callback output stream info: "
                    "%s (%d)", __FUNCTION__, mId,
                    strerror(-res), res);
            return res;
        }
        if (currentWidth != (uint32_t)params.previewWidth ||
                currentHeight != (uint32_t)params.previewHeight ||
                currentFormat != (uint32_t)callbackFormat) {
            // Since size should only change while preview is not running,
            // assuming that all existing use of old callback stream is
            // completed.
            ALOGV("%s: Camera %d: Deleting stream %d since the buffer "
                    "parameters changed", __FUNCTION__, mId, mCallbackStreamId);
            res = device->deleteStream(mCallbackStreamId);
            if (res != OK) {
                ALOGE("%s: Camera %d: Unable to delete old output stream "
                        "for callbacks: %s (%d)", __FUNCTION__,
                        mId, strerror(-res), res);
                return res;
            }
            mCallbackStreamId = NO_STREAM;
        }
    }

    if (mCallbackStreamId == NO_STREAM) {
        ALOGV("Creating callback stream: %d x %d, format 0x%x, API format 0x%x",
                params.previewWidth, params.previewHeight,
                callbackFormat, params.previewFormat);
        res = device->createStream(mCallbackWindow,
                params.previewWidth, params.previewHeight,
                callbackFormat, &mCallbackStreamId);//Creating callback stream
        if (res != OK) {
            ALOGE("%s: Camera %d: Can't create output stream for callbacks: "
                    "%s (%d)", __FUNCTION__, mId,
                    strerror(-res), res);
            return res;
        }
    }

    return OK;
}

对比updatePreviewStream可以发现，该函数自助创建了一套surface/BufferQueue/CpuConsumer的机制，这套类似SurfaceFlinger的buffer管理机制可参看一文Android5.1中 surface生产者和消费者间的处理框架简述。此外通过createStream请求Camera3Device建立一个Stream，其中Stream的ID值保存在mCallBackStreamId当中，并将一个CallbackWindow和当前的Stream绑定。

通过这个对比，也需要重点关注到，对于每个Camera3OutPutStream来说，每一个stream都被一个Consumer，而在此处都是Surface(ANativeWindow)所拥有，这个Consumer和HAL相匹配来说是消费者，但对于真正的处理Buffer的Consumer来说如CPUConsumer，Surface却又是以一个Product的角色存在的。

（3）updateProcessorStream(mJpegProcessor, params)

status_t Camera2Client::updateProcessorStream(sp processor,
                                              camera2::Parameters params) {
    // No default template arguments until C++11, so we need this overload
    return updateProcessorStream(
            processor, params);
}
template <typename ProcessorT,
          status_t (ProcessorT::*updateStreamF)(const Parameters &)>
status_t Camera2Client::updateProcessorStream(sp processor,
                                              Parameters params) {
    status_t res;

    // Get raw pointer since sp doesn't have operator->*
    ProcessorT *processorPtr = processor.get();
    res = (processorPtr->*updateStreamF)(params);
.......
}

该模板函数处理过程最终通过非显示实例到显示实例调用JpegProcessor::updateStream，该函数处理的逻辑基本和Callback模块处理一致，创建的一个OutPutStream和CaptureWindow相互绑定，同时Stream的ID保存在mCaptureStreamId中。

此外需要说明一点：

在preview模式下，就去创建一个jpeg处理的stream，目的在于启动takepicture时，可以更快的进行capture操作。是通过牺牲内存空间来提升效率。

（4）整合startPreviewL中所有的stream 到Vector outputStreams

outputStreams.push(getPreviewStreamId());//预览stream

outputStreams.push(getCallbackStreamId())//Callback stream

目前一次Preview构建的stream数目至少为两个。

（5）mStreamingProcessor->updatePreviewRequest()

在创建好多路stream后，由StreamingProcessor模块来将所有的stream信息交由Camera3Device去打包成Request请求。

注意：

Camera HAL2/3的特点是：将所有stream的请求都转化为几个典型的Request请求，而这些Request需要由HAL去解析，进而处理所需的业务。这也是Camera3数据处理复杂化的原因所在。

status_t StreamingProcessor::updatePreviewRequest(const Parameters ¶ms) {
    ATRACE_CALL();
    status_t res;
    sp device = mDevice.promote();
    if (device == 0) {
        ALOGE("%s: Camera %d: Device does not exist", __FUNCTION__, mId);
        return INVALID_OPERATION;
    }

    Mutex::Autolock m(mMutex);
    if (mPreviewRequest.entryCount() == 0) {
        sp client = mClient.promote();
        if (client == 0) {
            ALOGE("%s: Camera %d: Client does not exist", __FUNCTION__, mId);
            return INVALID_OPERATION;
        }

        // Use CAMERA3_TEMPLATE_ZERO_SHUTTER_LAG for ZSL streaming case.
        if (client->getCameraDeviceVersion() >= CAMERA_DEVICE_API_VERSION_3_0) {
            if (params.zslMode && !params.recordingHint) {
                res = device->createDefaultRequest(CAMERA3_TEMPLATE_ZERO_SHUTTER_LAG,
                        &mPreviewRequest);
            } else {
                res = device->createDefaultRequest(CAMERA3_TEMPLATE_PREVIEW,
                        &mPreviewRequest);
            }
        } else {
            res = device->createDefaultRequest(CAMERA2_TEMPLATE_PREVIEW,
                    &mPreviewRequest);//创建一个Preview相关的request，由底层的hal来完成default创建
        }

        if (res != OK) {
            ALOGE("%s: Camera %d: Unable to create default preview request: "
                    "%s (%d)", __FUNCTION__, mId, strerror(-res), res);
            return res;
        }
    }

    res = params.updateRequest(&mPreviewRequest);//根据参数来更新CameraMetadata request
    if (res != OK) {
        ALOGE("%s: Camera %d: Unable to update common entries of preview "
                "request: %s (%d)", __FUNCTION__, mId,
                strerror(-res), res);
        return res;
    }

    res = mPreviewRequest.update(ANDROID_REQUEST_ID,
            &mPreviewRequestId, 1);//mPreviewRequest的ANDROID_REQUEST_ID
    if (res != OK) {
        ALOGE("%s: Camera %d: Unable to update request id for preview: %s (%d)",
                __FUNCTION__, mId, strerror(-res), res);
        return res;
    }

    return OK;
}"color:#ff0000;">

该函数的处理过程是一个构建并初始化 mPreviewRequest的过程，分以下几个流程来分析：

a mPreviewRequest是一个CameraMetadata类型数据，用于封装当前previewRequest。

b device->createDefaultRequest(CAMERA3_TEMPLATE_PREVIEW, &mPreviewRequest)

const camera_metadata_t *rawRequest;
 ATRACE_BEGIN("camera3->construct_default_request_settings");
 rawRequest = mHal3Device->ops->construct_default_request_settings(
     mHal3Device, templateId);
 ATRACE_END();
 if (rawRequest == NULL) {
     SET_ERR_L("HAL is unable to construct default settings for template %d",
             templateId);
     return DEAD_OBJECT;
 }
 *request = rawRequest;
 mRequestTemplateCache[templateId] = rawRequest;

最终是由hal来实现构建一个rawrequest,即对于Preview，而言是构建了一个 CAMERA3_TEMPLATE_PREVIEW类型的Request。其实对HAL而言，rawrequest本质是用于操作一个camera_metadata_t类型的数据：

struct camera_metadata {
    metadata_size_t          size;
    uint32_t                 version;
    uint32_t                 flags;
    metadata_size_t          entry_count;
    metadata_size_t          entry_capacity;
    metadata_uptrdiff_t      entries_start; // Offset from camera_metadata
    metadata_size_t          data_count;
    metadata_size_t          data_capacity;
    metadata_uptrdiff_t      data_start; // Offset from camera_metadata
    uint8_t                  reserved[];
};

该数据结构可以存储多种数据，且可以根据entry tag的不同类型来存储数据，同时数据量的大小也可以自动调整。

c mPreviewRequest.update(ANDROID_REQUEST_ID,&mPreviewRequestId, 1)

将当前的PreviewRequest相应的ID保存到camera metadata。

（6）mStreamingProcessor->startStream启动整个预览的stream流

该函数的处理过程较为复杂，可以说是整个Preview正常工作的核心控制

status_t StreamingProcessor::startStream(StreamType type,
        const Vector &outputStreams) {
.....
CameraMetadata &request = (type == PREVIEW) ?
            mPreviewRequest : mRecordingRequest;//取preview的CameraMetadata request
....res = request.update(
    ANDROID_REQUEST_OUTPUT_STREAMS,
        outputStreams);//CameraMetadata中添加outputStreams
 res = device->setStreamingRequest(request);//向hal发送request
.....
}

该函数首先是根据当前工作模式来确定StreamingProcessor需要处理的Request，该模块负责Preview和Record两个Request。

以PreviewRequest就是之前createDefaultRequest构建的，这里先是将这个Request所需要操作的Outputstream打包到一个tag叫ANDROID_REQUEST_OUTPUT_STREAMS的entry当中。

a:setStreamingRequest

真正的请求Camera3Device去处理这个带有多路stream的PreviewRequest。

status_t Camera3Device::setStreamingRequest(const CameraMetadata &request,
                                            int64_t* /*lastFrameNumber*/) {
    ATRACE_CALL();

    List<const CameraMetadata> requests;
    requests.push_back(request);
    return setStreamingRequestList(requests, /*lastFrameNumber*/NULL);
}

该函数将mPreviewRequest push到一个list，调用setStreamingRequestList

status_t Camera3Device::setStreamingRequestList(const List<const CameraMetadata> &requests,
                                                int64_t *lastFrameNumber) {
    ATRACE_CALL();

    return submitRequestsHelper(requests, /*repeating*/true, lastFrameNumber);
}

status_t Camera3Device::submitRequestsHelper(
        const List<const CameraMetadata> &requests, bool repeating,
        /*out*/
        int64_t *lastFrameNumber) {//repeating = 1;lastFrameNumber = NULL
    ATRACE_CALL();
    Mutex::Autolock il(mInterfaceLock);
    Mutex::Autolock l(mLock);

    status_t res = checkStatusOkToCaptureLocked();
    if (res != OK) {
        // error logged by previous call
        return res;
    }

    RequestList requestList;

    res = convertMetadataListToRequestListLocked(requests, /*out*/&requestList);//返回的是CaptureRequest RequestList
    if (res != OK) {
        // error logged by previous call
        return res;
    }

    if (repeating) {
        res = mRequestThread->setRepeatingRequests(requestList, lastFrameNumber);//重复的request存入到RequestThread
    } else {
        res = mRequestThread->queueRequestList(requestList, lastFrameNumber);//capture模式，拍照单词
    }

    if (res == OK) {
        waitUntilStateThenRelock(/*active*/true, kActiveTimeout);
        if (res != OK) {
            SET_ERR_L("Can't transition to active in %f seconds!",
                    kActiveTimeout/1e9);
        }
        ALOGV("Camera %d: Capture request %" PRId32 " enqueued", mId,
              (*(requestList.begin()))->mResultExtras.requestId);
    } else {
        CLOGE("Cannot queue request. Impossible.");
        return BAD_VALUE;
    }

    return res;
}

b convertMetadataListToRequestListLocked

这个函数是需要将Requestlist中保存的CameraMetadata数据转换为List >

status_t Camera3Device::convertMetadataListToRequestListLocked(
        const List<const CameraMetadata> &metadataList, RequestList *requestList) {
    if (requestList == NULL) {
        CLOGE("requestList cannot be NULL.");
        return BAD_VALUE;
    }

    int32_t burstId = 0;
    for (List<const CameraMetadata>::const_iterator it = metadataList.begin();//CameraMetadata, mPreviewRequest
            it != metadataList.end(); ++it) {
        sp newRequest = setUpRequestLocked(*it);//新建CaptureRequest由CameraMetadata转化而来
        if (newRequest == 0) {
            CLOGE("Can't create capture request");
            return BAD_VALUE;
        }

        // Setup burst Id and request Id
        newRequest->mResultExtras.burstId = burstId++;
        if (it->exists(ANDROID_REQUEST_ID)) {
            if (it->find(ANDROID_REQUEST_ID).count == 0) {
                CLOGE("RequestID entry exists; but must not be empty in metadata");
                return BAD_VALUE;
            }
            newRequest->mResultExtras.requestId = it->find(ANDROID_REQUEST_ID).data.i32[0];//设置该request对应的id
        } else {
            CLOGE("RequestID does not exist in metadata");
            return BAD_VALUE;
        }

        requestList->push_back(newRequest);

        ALOGV("%s: requestId = %" PRId32, __FUNCTION__, newRequest->mResultExtras.requestId);
    }
    return OK;
}

这里是对List进行迭代解析处理，如当前模式下仅存在PreviewRequest这一个CameraMetadata，通过setUpRequestLocked将其转换为一个CaptureRequest。

c 重点来关注setUpRequestLocked复杂的处理过程

sp Camera3Device::setUpRequestLocked(
        const CameraMetadata &request) {//mPreviewRequest
    status_t res;

    if (mStatus == STATUS_UNCONFIGURED || mNeedConfig) {
        res = configureStreamsLocked();
      ......
    sp newRequest = createCaptureRequest(request);//CameraMetadata转为CaptureRequest，包含mOutputStreams
    return newRequest;
}

configureStreamsLocked函数主要是将Camera3Device侧建立的所有Stream包括Output与InPut格式的交由HAL3层的Device去实现处理的核心接口是configure_streams与register_stream_buffer。该部分内容会涉及到更多的数据流，详细的处理过程会放在下一博文中进行分析。

createCaptureRequest函数是将一个CameraMetadata格式的数据如PreviewRequest转换为一个CaptureRequest：

sp Camera3Device::createCaptureRequest(
        const CameraMetadata &request) {//mPreviewRequest
    ATRACE_CALL();
    status_t res;

    sp newRequest = new CaptureRequest;
    newRequest->mSettings = request;//CameraMetadata

    camera_metadata_entry_t inputStreams =
            newRequest->mSettings.find(ANDROID_REQUEST_INPUT_STREAMS);
    if (inputStreams.count > 0) {
        if (mInputStream == NULL ||
                mInputStream->getId() != inputStreams.data.i32[0]) {
            CLOGE("Request references unknown input stream %d",
                    inputStreams.data.u8[0]);
            return NULL;
        }
        // Lazy completion of stream configuration (allocation/registration)
        // on first use
        if (mInputStream->isConfiguring()) {
            res = mInputStream->finishConfiguration(mHal3Device);
            if (res != OK) {
                SET_ERR_L("Unable to finish configuring input stream %d:"
                        " %s (%d)",
                        mInputStream->getId(), strerror(-res), res);
                return NULL;
            }
        }

        newRequest->mInputStream = mInputStream;
        newRequest->mSettings.erase(ANDROID_REQUEST_INPUT_STREAMS);
    }

    camera_metadata_entry_t streams =
            newRequest->mSettings.find(ANDROID_REQUEST_OUTPUT_STREAMS);//读取存储在CameraMetadata的stream id信息
    if (streams.count == 0) {
        CLOGE("Zero output streams specified!");
        return NULL;
    }

    for (size_t i = 0; i < streams.count; i++) {
        int idx = mOutputStreams.indexOfKey(streams.data.i32[i]);//Camera3OutputStream的id在mOutputStreams中
        if (idx == NAME_NOT_FOUND) {
            CLOGE("Request references unknown stream %d",
                    streams.data.u8[i]);
            return NULL;
        }
        sp stream =
                mOutputStreams.editValueAt(idx);//返回的是Camera3OutputStream，preview/callback等stream

        // Lazy completion of stream configuration (allocation/registration)
        // on first use
        if (stream->isConfiguring()) {//STATE_IN_CONFIG或者STATE_IN_RECONFIG
            res = stream->finishConfiguration(mHal3Device);//register_stream_buffer， STATE_CONFIGURED
            if (res != OK) {
                SET_ERR_L("Unable to finish configuring stream %d: %s (%d)",
                        stream->getId(), strerror(-res), res);
                return NULL;
            }
        }

        newRequest->mOutputStreams.push(stream);//Camera3OutputStream添加到CaptureRequest的mOutputStreams
    }
    newRequest->mSettings.erase(ANDROID_REQUEST_OUTPUT_STREAMS);

    return newRequest;
}

该函数主要处理指定的这个CameraMetadata mPreviewRequest下对应所拥有的Output与Input Stream，对于Preview而言，至少存在OutPutStream包括一路StreamProcessor与一路可选的CallbackProcessor。

在构建这个PreviewRequest时，已经将ANDROID_REQUEST_OUTPUT_STREAMS这个Tag进行了初始化，相应的内容为Vector &outputStreams，包含着属于PreviewRequest这个Request所需要的输出stream的ID值，通过这个ID index值，可以遍历到Camera3Device下所createstream创造的Camera3OutputStream，即说明不同类型的Request在Camera3Device端存在多个Stream，而每次不同业务下所需要Request的对应的Stream又仅是其中的个别而已。

idx =  mOutputStreams.indexOfKey(streams.data.i32[i])是通过属于PreviewRequest中包含的一个stream的ID值来查找到mOutputStreams这个KeyedVector中对应的标定值index。注意：两个索引值不一定是一致的。

mOutputStreams.editValueAt(idx)是获取一个与该ID值(如Previewstream ID、Callback Stream ID等等)相对应的Camera3OutputStream。

在找到了当前Request中所有的Camera3OutputStream后，将其维护在CaptureRequest中

class CaptureRequest : public LightRefBase {
      public:
        CameraMetadata                      mSettings;
        sp          mInputStream;
        Vector >
                                            mOutputStreams;
        CaptureResultExtras                 mResultExtras;
    };

mSettings是保存CameraMetadata PreviewRequest，vector mOutPutStreams保存着当前Request提取出来的 Camera3OutputStream，至此构建了一个CaptureRequest。

返回到convertMetadataListToRequestListLocked中，现在已经完成了一个CameraMetadata Request的处理，生产的是一个CaptureRequest。我们将这个ANDROID_REQUEST_ID的ID值，保留在

newRequest->mResultExtras.requestId = it->find(ANDROID_REQUEST_ID).data.i32[0]。

这个值在整个Camera3的架构中，仅存在3大种Request类型，说明了整个和HAL层交互的Request类型是不多的：

预览Request mPreviewRequest：        mPreviewRequestId(Camera2Client::kPreviewRequestIdStart),

拍照Request mCaptureRequest：mCaptureId(Camera2Client::kCaptureRequestIdStart),

录像Request mRecordingRequest：        mRecordingRequestId(Camera2Client::kRecordingRequestIdStart),

static const int32_t kPreviewRequestIdStart = 10000000;
static const int32_t kPreviewRequestIdEnd   = 20000000;
static const int32_t kRecordingRequestIdStart  = 20000000;
static const int32_t kRecordingRequestIdEnd    = 30000000;
static const int32_t kCaptureRequestIdStart = 30000000;
static const int32_t kCaptureRequestIdEnd   = 40000000;

至此执行requestList->push_back(newRequest)后生成了一个 requestList，本质上可以先认为这次仅是含有PreviewRequest相关的内容。

d mRequestThread->setRepeatingRequests(requestList)

对于Preview来说，一次Preview后底层硬件就该可以连续的工作，而不需要进行过多的切换，故Framework每次向HAL发送的Request均是一种repeat的操作模式，故调用了一个重复的RequestQueue来循环处理每次的Request。

status_t Camera3Device::RequestThread::setRepeatingRequests(
        const RequestList &requests,
        /*out*/
        int64_t *lastFrameNumber) {
    Mutex::Autolock l(mRequestLock);
    if (lastFrameNumber != NULL) {//第一次进来为null
        *lastFrameNumber = mRepeatingLastFrameNumber;
    }
    mRepeatingRequests.clear();
    mRepeatingRequests.insert(mRepeatingRequests.begin(),
            requests.begin(), requests.end());

    unpauseForNewRequests();//signal request_thread in waitfornextrequest

    mRepeatingLastFrameNumber = NO_IN_FLIGHT_REPEATING_FRAMES;
    return OK;
}

将Preview线程提交的Request加入到mRepeatingRequests中后，唤醒RequestThread线程去处理当前新的Request。

(7) RequestThread 请求处理线程

RequestThread::threadLoop()函数主要用于响应并处理新加入到Request队列中的请求。

bool Camera3Device::RequestThread::threadLoop() {
....
    sp nextRequest = waitForNextRequest();//返回的是mRepeatingRequests，mPreviewRequest
    if (nextRequest == NULL) {
        return true;
    }
    // Create request to HAL
    camera3_capture_request_t request = camera3_capture_request_t();//CaptureRequest转为给HAL3.0的camera3_capture_request_t
    request.frame_number = nextRequest->mResultExtras.frameNumber;//当前帧号
    Vector outputBuffers;
    // Get the request ID, if any
    int requestId;
    camera_metadata_entry_t requestIdEntry =
            nextRequest->mSettings.find(ANDROID_REQUEST_ID);
    if (requestIdEntry.count > 0) {
        requestId = requestIdEntry.data.i32[0];//获取requestid,这里是mPreviewRequest的id
    } else {
        ALOGW("%s: Did not have android.request.id set in the request",
                __FUNCTION__);
        requestId = NAME_NOT_FOUND;
    }
 .....
    camera3_stream_buffer_t inputBuffer;
    uint32_t totalNumBuffers = 0;
.....
    // Submit request and block until ready for next one
    ATRACE_ASYNC_BEGIN("frame capture", request.frame_number);
    ATRACE_BEGIN("camera3->process_capture_request");
    res = mHal3Device->ops->process_capture_request(mHal3Device, &request);//调用底层的process_capture_request
    ATRACE_END();

   .......
}

函数主体内容较为复杂，分以下几个部分来说明他的响应逻辑：

(7.1) waitForNextRequest()

    Camera3Device::RequestThread::waitForNextRequest() {
status_t res;
sp nextRequest;

// Optimized a bit for the simple steady-state case (single repeating
// request), to avoid putting that request in the queue temporarily.
Mutex::Autolock l(mRequestLock);

while (mRequestQueue.empty()) {
    if (!mRepeatingRequests.empty()) {
        // Always atomically enqueue all requests in a repeating request
        // list. Guarantees a complete in-sequence set of captures to
        // application.
        const RequestList &requests = mRepeatingRequests;
        RequestList::const_iterator firstRequest =
                requests.begin();
        nextRequest = *firstRequest;//取
        mRequestQueue.insert(mRequestQueue.end(),
                ++firstRequest,
                requests.end());//把当前的mRepeatingRequests插入到mRequestQueue
        // No need to wait any longer

        mRepeatingLastFrameNumber = mFrameNumber + requests.size() - 1;

        break;
    }

    res = mRequestSignal.waitRelative(mRequestLock, kRequestTimeout);//等待下一个request

    if ((mRequestQueue.empty() && mRepeatingRequests.empty()) ||
            exitPending()) {
        Mutex::Autolock pl(mPauseLock);
        if (mPaused == false) {
            ALOGV("%s: RequestThread: Going idle", __FUNCTION__);
            mPaused = true;
            // Let the tracker know
            sp statusTracker = mStatusTracker.promote();
            if (statusTracker != 0) {
                statusTracker->markComponentIdle(mStatusId, Fence::NO_FENCE);
            }
        }
        // Stop waiting for now and let thread management happen
        return NULL;
    }
}

if (nextRequest == NULL) {
    // Don't have a repeating request already in hand, so queue
    // must have an entry now.
    RequestList::iterator firstRequest =
            mRequestQueue.begin();
    nextRequest = *firstRequest;
    mRequestQueue.erase(firstRequest);//取一根mRequestQueue中的CaptureRequest，来自于mRepeatingRequests的next
}

// In case we've been unpaused by setPaused clearing mDoPause, need to
// update internal pause state (capture/setRepeatingRequest unpause
// directly).
Mutex::Autolock pl(mPauseLock);
if (mPaused) {
    ALOGV("%s: RequestThread: Unpaused", __FUNCTION__);
    sp statusTracker = mStatusTracker.promote();
    if (statusTracker != 0) {
        statusTracker->markComponentActive(mStatusId);
    }
}
mPaused = false;

// Check if we've reconfigured since last time, and reset the preview
// request if so. Can't use 'NULL request == repeat' across configure calls.
if (mReconfigured) {
    mPrevRequest.clear();
    mReconfigured = false;
}

if (nextRequest != NULL) {
    nextRequest->mResultExtras.frameNumber = mFrameNumber++;//对每一个非空的request需要帧号++
    nextRequest->mResultExtras.afTriggerId = mCurrentAfTriggerId;
    nextRequest->mResultExtras.precaptureTriggerId = mCurrentPreCaptureTriggerId;
}
return nextRequest;

该函数是响应RequestList的核心，通过不断的轮训休眠等待一旦mRepeatingRequests有Request可处理时，就将他内部所有的 CaptureRequest加入到 mRequestQueue 中去，理论来说每一个CaptureRequest对应着一帧的请求处理，每次响应时可能会出现mRequestQueue包含了多个CaptureRequest。

通过nextRequest->mResultExtras.frameNumber = mFrameNumber++表示当前CaptureRequest在处理的一帧图像号。

对于mRepeatingRequests而言，只有其非空，在执行完一次queue操作后，在循环进入执行时，会自动对mRequestQueue进行erase操作，是的mRequestQueue变为empty后再次重新加载mRepeatingRequests中的内容，从而形成一个队repeatRequest的重复响应过程。

(7.2)   camera_metadata_entry_t requestIdEntry = nextRequest->mSettings.find(ANDROID_REQUEST_ID);提取该CaptureRequest对应的Request 类型值

(7.3) getBuffer操作

涉及到比较复杂的数据流操作过程的内容见下一博文

(7.4) mHal3Device->ops->process_capture_request(mHal3Device, &request)

这里的request是已经由一个CaptureRequest转换为和HAL3.0交互的camera3_capture_request_t结构。

8 小结

至此已经完成了一次向HAL3.0 Device发送一次完整的Request的请求。从最初Preview启动建立多个OutPutStream，再是将这些Stream打包成一个mPreviewRequest来启动stream，随后将这个Request又转变为一个CaptureRequest，直到转为Capture list后交由RequestThread来处理这些请求。每一次的Request简单可以说是Camera3Device向HAL3.0请求一帧数据，当然每一次Request也可以包含各种控制操作，如AutoFocus等内容，会在后续补充。

到这里从StartPreview的入口开始，直到相应的Request下发到HAL3.0，基本描述了一次完成的控制流的处理。对于较为复杂的数据流本质也是一并合并在这个控制操作中的，但作为Buffer视频缓存流的管理维护将在下一博文进行描述与总结。