转：ffos:Firefox OS启动过程分析－b2g进程启动

https://blog.csdn.net/zembers/article/details/48495627

b2g启动时，运行”/system/b2g/b2g”，入口在”gecko/b2g/app/B2GLoader.cpp”中，如下：

int main(int argc, const char* argv[]) { /** * Reserve file descriptors before loading static data. */ FdArray reservedFds; ReserveFileDescriptors(reservedFds); /* * Before fork(), libxul and static data of Gecko are loaded for * sharing. */ bool ok = LoadStaticData(argc, argv); if (!ok) { return 255; } return RunProcesses(argc, argv, reservedFds);

代码执行流程如下所示：

main() (b2g/app/B2GLoader.cpp) | |-ReserveFileDescriptors | |-LoadStaticData | |-RunProcesses | |-fork | |-XRE_ProcLoaderServiceRun (child(nuwa) process) | |-b2g_main (parent(b2g) process) (b2g/app/nsBrowserApp.cpp) | |-android::ProcessState::self()->startThreadPool(); | |-(void)setsid(); | |-do_main | |-mozilla::StartBootAnimation(); | |-XRE_main | |-XREMain::XRE_main | |-new ScopedAppData(aAppData); | |-XREMain::XRE_mainInit | |-XREMain::XRE_mainStartup | |-mScopedXPCOM = MakeUnique<ScopedXPCOMStartup>(); | |-mScopedXPCOM->Initialize(); (toolkit/xre/nsAppRunner.cpp) | | | |-NS_InitXPCOM2 (xpcom/build/XPCOMInit.cpp) | | | |-sMessageLoop = new MessageLoopForUI(MessageLoop::TYPE_MOZILLA_UI); | | | |-ioThread = MakeUnique<BrowserProcessSubThread>(BrowserProcessSubThread::IO); | |-ioThread->StartWithOptions | | | |-nsThreadManager::get()->Init(); | | | |-nsTimerImpl::Startup(); | | | |-nsComponentManagerImpl::gComponentManager = new nsComponentManagerImpl(); | | | |-nsCycleCollector_init | | | |-nsCycleCollector_startup | | | |-JS_Init | | | |-nsComponentManagerImpl::gComponentManager->Init();(xpcom/components/nsComponentManager.cpp) | | | | | |-nsComponentManagerImpl::InitializeStaticModules() | | | | | |-RegisterModule(...) | | | | | |-greOmnijar = mozilla::Omnijar::GetReader(mozilla::Omnijar::GRE); | | | | | |-cl->location.Init(greOmnijar, "chrome.manifest"); | | | | | |-nsComponentManagerImpl::RereadChromeManifests | | | | | |-nsComponentManagerImpl::RegisterManifest | | | | | |-DoRegisterManifest | | | | | |-ParseManifest | | | | | |-... | | | | | |-nsComponentManagerImpl::ManifestContract | | | |-XPTInterfaceInfoManager::GetSingleton(); | | | |-nsDirectoryService::gService->RegisterCategoryProviders(); | | | |-SharedThreadPool::InitStatics(); | | | |-AbstractThread::InitStatics(); | | | |-mozilla::scache::StartupCache::GetSingleton(); | | | |-mozilla::AvailableMemoryTracker::Activate(); | | | |-NS_CreateServicesFromCategory(...) | | | |-mozilla::HangMonitor::Startup(); | | | |-mozilla::BackgroundHangMonitor::Startup(); | | | |-sMainHangMonitor = new mozilla::BackgroundHangMonitor | |-XREMain::XRE_mainRun() | |-mozilla::ipc::ProcLoaderClientGeckoInit(); | |-mScopedXPCOM->SetWindowCreator(mNativeApp); | |-startupNotifier->Observe(nullptr, APPSTARTUP_TOPIC, nullptr); | |-mDirProvider.DoStartup(); | |-cmdLine->Init(...) | |-obsService->NotifyObservers(cmdLine, "command-line-startup", nullptr); | |-appStartup->CreateHiddenWindow(); | |-obsService->NotifyObservers(nullptr, "final-ui-startup", nullptr); | |-cmdLine->Run(); (toolkit/components/commandlines/nsCommandLine.cpp) | | | |- nsCommandLine::EnumerateValidators | | | |-nsCommandLine::EnumerateHandlers | | | |-EnumRun | | | |-nsICommandLineHandler->Handle (first page will be loaded in here) | |-mNativeApp->Enable(); | |-appStartup->Run(); (toolkit/components/startup/nsAppStartup.cpp) | |-mAppShell->Run(); (widget/gonk/nsAppShell.cpp->widget/nsBaseAppShell.cpp) | |-MessageLoop::current()->Run(); // run forever~~~~~

b2g进程启动中，会做以下几件事： 1. 在加载库文件之前保留5个文件描述符（从STDERR_FILENO+1开始）

FdArray reservedFds; ReserveFileDescriptors(reservedFds);

2.加载进程间能共享的各种数据（主要加载libxul等各种共享库，从Omnijar文件中加载各种模块的xpt信息），这样可以节约些内存。

bool ok = LoadStaticData(argc, argv); 1

3.开始fork进程。父亲就是b2g进程，儿子就是nuwa进程（后续再讲）。其中b2g进程具有系统root权限，负责处理系统的io，显示，操作底层硬件等。 在b2g进程中运行后，需要初始化xpcom，即调用：

rv = NS_InitXPCOM2(&mServiceManager,gDirServiceProvider->GetAppDir(), gDirServiceProvider); 1

最后，b2g进程会进入一个message loop中，等待处理各种请求：

appStartup->Run(); 1

---

Firefox OS中进程可以分为三类：b2g进程，nuwa进程，以及content进程。其中content进程都是由nuwa进程生成的（当然在nuwa进程未ready，但又需要fork进程的时候，有可能会由b2g进程直接生成）。

nuwa进程是如何创建新进程？b2g是如何加载第一个程序(system)的？后续文章中进行讲解。