第8讲 cameraserver进程启动之enumerateProviders概述

Charles · 2024 年8 月 26 日 00:04

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：

资源	描述
在线课程	极客笔记在线课程
知识星球	星球名称：深入浅出Android Camera 星球ID: 17296815
Wechat	极客笔记圈

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

创建CameraProviderManager，并调用initialize完成初始化
初始化 VendorTags
初始化Flashlight并完成枚举动作
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&lt;std::string&gt; deviceIds;
{
    Mutex::Autolock l(mServiceLock);

    if (nullptr == mCameraProviderManager.get()) {
        mCameraProviderManager = new CameraProviderManager();
        res = mCameraProviderManager-&gt;initialize(this);
        if (res != OK) {
            ALOGE(&quot;%s: Unable to initialize camera provider manager: %s (%d)&quot;,
                    __FUNCTION__, strerror(-res), res);
            logServiceError(String8::format(&quot;Unable to initialize camera provider manager&quot;),
            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-&gt;setUpVendorTags();

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

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

    deviceIds = mCameraProviderManager-&gt;getCameraDeviceIds();
}

for (auto&amp; 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;

}