代码入口

frameworks/av/camera/cameraserver

里面包含了四个文件

我们先来看看Android.bp的内容

package {// See: http://go/android-license-faq// A large-scale-change added 'default_applicable_licenses' to import// all of the 'license_kinds' from "frameworks_av_camera_license"// to get the below license kinds://   SPDX-license-identifier-Apache-2.0default_applicable_licenses: ["frameworks_av_camera_license"],
}cc_binary {name: "cameraserver",srcs: ["main_cameraserver.cpp"],header_libs: ["libmedia_headers",],shared_libs: ["libcameraservice","liblog","libutils","libui","libgui","libbinder","libhidlbase","android.hardware.camera.common@1.0","android.hardware.camera.provider@2.4","android.hardware.camera.provider@2.5","android.hardware.camera.provider@2.6","android.hardware.camera.provider@2.7","android.hardware.camera.provider-V1-ndk","android.hardware.camera.device@1.0","android.hardware.camera.device@3.2","android.hardware.camera.device@3.4",],compile_multilib: "first",cflags: ["-Wall","-Wextra","-Werror","-Wno-unused-parameter",],init_rc: ["cameraserver.rc"],vintf_fragments: ["manifest_android.frameworks.cameraservice.service@2.2.xml",],
}

 我们注意到

    init_rc: ["cameraserver.rc"],

由此可知系统在编译时会将cameraserver.rc放到system/etc/init目录下，
init进程启动的时候会解析这个目录下的所有.rc文件。 

solid/android13/amdroid13_ntls/out/target/product/hpg2_24/system/etc/init$ ll cameraserver.rc
-rw-rw-r-- 1 wancg wancg 214 3月   7 14:59 cameraserver.rc

 接下来我们来探探cameraserver.rc的庐山真面目：

service cameraserver /system/bin/cameraserverclass mainuser cameraservergroup audio camera input drmrpcioprio rt 4task_profiles CameraServiceCapacity MaxPerformancerlimit rtprio 10 10

开机时/system/bin/cameraserver启动一个名称为cameraserver的服务

再来看看main_cameraserver.cpp 的内容

#define LOG_TAG "cameraserver"
//#define LOG_NDEBUG 0#include "CameraService.h"
#include <hidl/HidlTransportSupport.h>using namespace android;int main(int argc __unused, char** argv __unused)
{signal(SIGPIPE, SIG_IGN);// Set 5 threads for HIDL calls. Now cameraserver will serve HIDL calls in// addition to consuming them from the Camera HAL as well.hardware::configureRpcThreadpool(5, /*willjoin*/ false);sp<ProcessState> proc(ProcessState::self());sp<IServiceManager> sm = defaultServiceManager();ALOGI("ServiceManager: %p", sm.get());CameraService::instantiate();//下面我们就从CameraService继续分析。ALOGI("ServiceManager: %p done instantiate", sm.get());ProcessState::self()->startThreadPool();IPCThreadState::self()->joinThreadPool();
}

 CarmeraServer.cpp

CameraService继承了BinderService.h.这个:instantiate()调用到了BinderService.h里的代码

frameworks/native/libs/binder/include/binder/BinderService.h
class BinderService
{
public:static status_t publish(bool allowIsolated = false,int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {sp<IServiceManager> sm(defaultServiceManager());return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated,dumpFlags);}static void publishAndJoinThreadPool(bool allowIsolated = false,int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {publish(allowIsolated, dumpFlags);joinThreadPool();}static void instantiate() { publish(); }static status_t shutdown() { return NO_ERROR; }private:static void joinThreadPool() {sp<ProcessState> ps(ProcessState::self());ps->startThreadPool();ps->giveThreadPoolName();IPCThreadState::self()->joinThreadPool();}
};

在回过头来看看上面提到的CameraService方法

// frameworks/av/services/camera/libcameraservice/CameraService.h
class CameraService :// 继承BinderService指定泛型类型为CameraServicepublic BinderService<CameraService>,public virtual ::android::hardware::BnCameraService,public virtual IBinder::DeathRecipient,public virtual CameraProviderManager::StatusListener
{...
public:...// 注册的binder服务名称为“media.camera”static char const* getServiceName() { return "media.camera"; }...
}

接下来我们看下frameworks/native/libs/binder/include/binder/BinderService.h 中提到addService方法

// frameworks/native/libs/binder/include/binder/IServiceManager.h
// 第一个参数是字符串media.camera
// 第二个参数是new的CameraService对象
// 这里相当于const sp<IBinder>& service = new CameraService()
virtual status_t addService(const String16& name, const sp<IBinder>& service,bool allowIsolated = false,int dumpsysFlags = DUMP_FLAG_PRIORITY_DEFAULT) = 0;

我们看下class sp的实现

// system/core/libutils/include/utils/StrongPointer.h
// 下面的T就是CameraService*
template <typename T>
sp<T>& sp<T>::operator=(T* other) {T* oldPtr(*const_cast<T* volatile*>(&m_ptr));if (other) {check_not_on_stack(other);// 可以看到如果指针不为空的话// 会调用自身的incStrong方法other->incStrong(this);}if (oldPtr) oldPtr->decStrong(this);if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();m_ptr = other;return *this;
}

 但是我们发现CameraService里并没有incStrong方法，那么一定
是它的父类的方法，由此引出了一个非常重要的类RefBase。
RefBase是Android中所有C++对象的基类。

从这个文件可以看出,instantiate最终还是调用到了IServiceManager里的addService, 将我们的cameraService注册到了系统的服务管理器里去了.

        这里调用到CameraService后, 因为是开机第一次调用,它的引用计数为1,所以会调用到CameraService::onFirstRef()这个函数. 这个函数是从CameraService的父类RefBase里继承过来的.该函数在强引用sp新增引用计数时调用，什么意思？就是当 有sp包装的类初始化的时候调用.我们再看看cameraService::onFirstRef()

frameworks\av\services\camera\libcameraservice\CameraService.cpp
void CameraService::onFirstRef()
{ALOGI("CameraService process starting");BnCameraService::onFirstRef();// Update battery life tracking if service is restartingBatteryNotifier& notifier(BatteryNotifier::getInstance());notifier.noteResetCamera();notifier.noteResetFlashlight();status_t res = INVALID_OPERATION;res = enumerateProviders();if (res == OK) {mInitialized = true;}mUidPolicy = new UidPolicy(this);mUidPolicy->registerSelf();mSensorPrivacyPolicy = new SensorPrivacyPolicy(this);mSensorPrivacyPolicy->registerSelf();mInjectionStatusListener = new InjectionStatusListener(this);mAppOps.setCameraAudioRestriction(mAudioRestriction);sp<HidlCameraService> hcs = HidlCameraService::getInstance(this);if (hcs->registerAsService() != android::OK) {ALOGE("%s: Failed to register default android.frameworks.cameraservice.service@1.0",__FUNCTION__);}// This needs to be last call in this function, so that it's as close to// ServiceManager::addService() as possible.CameraServiceProxyWrapper::pingCameraServiceProxy();ALOGI("CameraService pinged cameraservice proxy");
}

在这个函数里,我们只关注enumerateProviders(),这里就到了列出所有cameraProvider.

status_t CameraService::enumerateProviders() {status_t res;std::vector<std::string> deviceIds;std::unordered_map<std::string, std::set<std::string>> unavailPhysicalIds;{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(&unavailPhysicalIds);}for (auto& cameraId : deviceIds) {String8 id8 = String8(cameraId.c_str());if (getCameraState(id8) == nullptr) {onDeviceStatusChanged(id8, CameraDeviceStatus::PRESENT);}if (unavailPhysicalIds.count(cameraId) > 0) {for (const auto& physicalId : unavailPhysicalIds[cameraId]) {String8 physicalId8 = String8(physicalId.c_str());onDeviceStatusChanged(id8, physicalId8, CameraDeviceStatus::NOT_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;
}

这个函数里,创建了一个CameraProviderManager对象,并调进行了初始化.具体如下：