第8讲 cameraserver进程启动之enumerateProviders概述 - Android Cam

本讲是Android Camera Native Framework专题的第8讲，我们介绍cameraserver进程启动之enumerateProviders概述

更多资源：

Android Camera HAL接口简介

Android Camera HAL接口分成HIDL和AIDL两种，核心接口如下：

注：接口代码路径：/hardware/interfaces/camera/

解释：

• ICameraProvider管理多个ICameraDevice
• ICameraDevice管理和维护某一颗CameraDevice
• 通过ICameraProvider获取到ICameraDevice
• 通过ICameraDevice获取到ICameraDeviceSession
• 初始化时，ICameraProvider和ICameraDevice的实例就会被创建起来， ICameraDeviceSession要open camera时才创建，close camera时销毁

CameraService与CameraProviderManager的关系

CameraProviderManager

• 负责管理Camera HAL Providers

CameraService

• ICameraService的实现，CameraService与HAL Provider的交互要通过CameraProviderManager

CameraProviderManager中的ProviderInfo

CameraProviderManager抽象出ProviderInfo来屏蔽HIDL和AIDL Provider的差异，将差异部分交给HidlProviderInfo和AidlProviderInfo去处理。

enumerateProviders总体流程介绍

有哪些情况会调用到enumerateProviders

• CameraServer进程启动时（onFirstRef）
• CameraServer进程启动后，有新的Provider注册到ServiceManager时（onNewProviderRegistered）

总体流程代码介绍

1. 创建CameraProviderManager，并调用initialize完成初始化
2. 初始化 VendorTags
3. 初始化Flashlight并完成枚举动作
4. 针对主前/后摄，为SPerfClass过滤CameraCharacteristics
   • 参考CDD：2.2.7. Handheld Media Performance Class

代码基于Android 13:

status_t CameraService::enumerateProviders() {
    status_t res;

    std::vector 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);
                logServiceError(String8::format("Unable to initialize camera provider manager"),
                ERROR_DISCONNECTED);
                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());
        if (getCameraState(id8) == nullptr) {
            onDeviceStatusChanged(id8, CameraDeviceStatus::PRESENT);
        }
    }

    // Derive primary rear/front cameras, and filter their charactierstics.
    // This needs to be done after all cameras are enumerated and camera ids are sorted.
    if (SessionConfigurationUtils::IS_PERF_CLASS) {
        // Assume internal cameras are advertised from the same
        // provider. If multiple providers are registered at different time,
        // and each provider contains multiple internal color cameras, the current
        // logic may filter the characteristics of more than one front/rear color
        // cameras.
        Mutex::Autolock l(mServiceLock);
        filterSPerfClassCharacteristicsLocked();
    }

    return OK;
}

本文链接：http://so.lmcjl.com/news/16752/