cef源码分析之cefsimple

Posted 2021-03-16 lenomirei

下面是cefsimple的入口代码，主要分成两个部分

// Entry point function for all processes.
int APIENTRY wWinMain(HINSTANCE hInstance,
                      HINSTANCE hPrevInstance,
                      LPTSTR lpCmdLine,
                      int nCmdShow) {
  UNREFERENCED_PARAMETER(hPrevInstance);
  UNREFERENCED_PARAMETER(lpCmdLine);

  // Enable High-DPI support on Windows 7 or newer.
  CefEnableHighDPISupport();

  void* sandbox_info = NULL;

#if defined(CEF_USE_SANDBOX)
  // Manage the life span of the sandbox information object. This is necessary
  // for sandbox support on Windows. See cef_sandbox_win.h for complete details.
  CefScopedSandboxInfo scoped_sandbox;
  sandbox_info = scoped_sandbox.sandbox_info();
#endif

  // Provide CEF with command-line arguments.
  CefMainArgs main_args(hInstance);

  // CEF applications have multiple sub-processes (render, plugin, GPU, etc)
  // that share the same executable. This function checks the command-line and,
  // if this is a sub-process, executes the appropriate logic.
  int exit_code = CefExecuteProcess(main_args, NULL, sandbox_info);
  if (exit_code >= 0) {
    // The sub-process has completed so return here.
    return exit_code;
  }

  // Specify CEF global settings here.
  CefSettings settings;

#if !defined(CEF_USE_SANDBOX)
  settings.no_sandbox = true;
#endif

  // SimpleApp implements application-level callbacks for the browser process.
  // It will create the first browser instance in OnContextInitialized() after
  // CEF has initialized.
  CefRefPtr<SimpleApp> app(new SimpleApp);

  // Initialize CEF.
  CefInitialize(main_args, settings, app.get(), sandbox_info);

  // Run the CEF message loop. This will block until CefQuitMessageLoop() is
  // called.
  CefRunMessageLoop();

  // Shut down CEF.
  CefShutdown();

  return 0;
}

进程判断

首先是初始化进程的代码，cef的进程结构和chromium类似，都是多进程共用代码。所以cef提供了一些函数来检测主进程（即browser进程）的流程和子进程的流程，以分别执行适合当前执行进程的逻辑。这段代码如下所示。

// CEF applications have multiple sub-processes (render, plugin, GPU, etc)
  // that share the same executable. This function checks the command-line and,
  // if this is a sub-process, executes the appropriate logic.
  int exit_code = CefExecuteProcess(main_args, NULL, sandbox_info);
  if (exit_code >= 0) {
    // The sub-process has completed so return here.
    return exit_code;
  }

其中main_args用于获取当前进程的命令行参数，因为在chromium中，进程的区分就是靠命令行参数中的--type，如果是browser进程，则没有--type参数，其他进程该参数的值为renderer,gpu等

int CefExecuteProcess(const CefMainArgs& args,
                      CefRefPtr<CefApp> application,
                      void* windows_sandbox_info) {
#if defined(OS_WIN)
#if defined(ARCH_CPU_X86_64)
  DisableFMA3();
#endif
  InitInstallDetails();
  InitCrashReporter();
#endif

  base::CommandLine command_line(base::CommandLine::NO_PROGRAM);
#if defined(OS_WIN)
  command_line.ParseFromString(::GetCommandLineW());
#else
  command_line.InitFromArgv(args.argc, args.argv);
#endif

  // Wait for the debugger as early in process initialization as possible.
  if (command_line.HasSwitch(switches::kWaitForDebugger))
    base::debug::WaitForDebugger(60, true);

  // If no process type is specified then it represents the browser process and
  // we do nothing.
  std::string process_type =
      command_line.GetSwitchValueASCII(switches::kProcessType);
  if (process_type.empty())
    return -1;

#if defined(OS_MACOSX) || defined(OS_WIN)
  if (process_type == crash_reporter::switches::kCrashpadHandler)
    return RunAsCrashpadHandler(command_line);
#endif

  CefMainDelegate main_delegate(application);

// Execute the secondary process.
#if defined(OS_WIN)
  sandbox::SandboxInterfaceInfo sandbox_info = {0};
  if (windows_sandbox_info == NULL) {
    content::InitializeSandboxInfo(&sandbox_info);
    windows_sandbox_info = &sandbox_info;
  }

  content::ContentMainParams params(&main_delegate);
  params.instance = args.instance;
  params.sandbox_info =
      static_cast<sandbox::SandboxInterfaceInfo*>(windows_sandbox_info);

  return content::ContentMain(params);
#else
  content::ContentMainParams params(&main_delegate);
  params.argc = args.argc;
  params.argv = const_cast<const char**>(args.argv);

  return content::ContentMain(params);
#endif
}

只有当非browser进程时才会执行ContentMain函数，这也符合chromium的逻辑。ContentMain函数是其他子进程的入口点。
而browser进程则会返回执行CefInitialize和CefRunMessageLoop进入browser进程的主循环。当进程需要退出时，CefRunMessageLoop主循环退出，执行CefShutdown进程结束。

cef的browser进程启动

第二个部分就是browser进程的主流程，下面是拆分出来的代码。

  // Initialize CEF.
  CefInitialize(main_args, settings, app.get(), sandbox_info);

  // Run the CEF message loop. This will block until CefQuitMessageLoop() is
  // called.
  CefRunMessageLoop();

  // Shut down CEF.
  CefShutdown();

首先看CefInitialize初始化函数，其中app.get()即CefApp对象指针的参数尤为重要，在文件libcef/browser/context.cc中，提供了不少类似CefInitialize的cef控制函数，初始化，关闭，开启和退出消息循环等

bool CefInitialize(const CefMainArgs& args,
                   const CefSettings& settings,
                   CefRefPtr<CefApp> application,
                   void* windows_sandbox_info) {
#if defined(OS_WIN)
#if defined(ARCH_CPU_X86_64)
  DisableFMA3();
#endif
  InitInstallDetails();
  InitCrashReporter();
#endif

  // Return true if the global context already exists.
  if (g_context)
    return true;

  if (settings.size != sizeof(cef_settings_t)) {
    NOTREACHED() << "invalid CefSettings structure size";
    return false;
  }

  g_browser_process = new ChromeBrowserProcessStub();

  // Create the new global context object.
  g_context = new CefContext();

  // Initialize the global context.
  return g_context->Initialize(args, settings, application,
                               windows_sandbox_info);
}

为的是创建一个全局的Context对象，只有当Context对象被创建完成后，才能进行CreateBrowser操作，在下面的代码中

return g_context->Initialize(args, settings, application,
                               windows_sandbox_info);

Initialize的主要作用是根据content api开始做浏览器进程启动准备。因为content api要涉及chromium代码，这里就不继续往下追溯，主要看cef的流程

bool CefContext::Initialize(const CefMainArgs& args,
                            const CefSettings& settings,
                            CefRefPtr<CefApp> application,
                            void* windows_sandbox_info) {
...
  main_delegate_.reset(new CefMainDelegate(application));
...
  if (CEF_CURRENTLY_ON_UIT()) {
    OnContextInitialized();
  } else {
    // Continue initialization on the UI thread.
    CEF_POST_TASK(CEF_UIT, base::Bind(&CefContext::OnContextInitialized,
                                      base::Unretained(this)));
  }
...

CefApp的引用会一直传递到这里，当初始化的流程结束的时候（OnContextInitialized），就到了CefApp发挥作用的时候了。

其中main_delegate_作为一个代理，主要代理总体管理的相关功能，包括资源初始化，浏览器关闭等。那么CefApp对它有什么用呢？主要是为了创建一个全局的CefContentClient对象。

CefMainDelegate::CefMainDelegate(CefRefPtr<CefApp> application)
    : content_client_(application) {

然后当CefContext初始化完成后，就会从这个全局的CefContentClient对象中获取CefApp的引用。而获得引用之后是为了获得handler，以完成对应的回调。

void CefContext::OnContextInitialized() {
  CEF_REQUIRE_UIT();

  static_cast<ChromeBrowserProcessStub*>(g_browser_process)
      ->OnContextInitialized();

#if BUILDFLAG(ENABLE_WIDEVINE) && BUILDFLAG(ENABLE_LIBRARY_CDMS)
  CefWidevineLoader::GetInstance()->OnContextInitialized();
#endif

  // Notify the handler.
  CefRefPtr<CefApp> app = CefContentClient::Get()->application();
  if (app.get()) {
    CefRefPtr<CefBrowserProcessHandler> handler =
        app->GetBrowserProcessHandler();
    if (handler.get())
      handler->OnContextInitialized();
  }
}

此处主要获取的是browser process handler，这个handler的主要目的是监控并触发browser进程生命周期内各个关键时机的回调。

如果多少用过cef，会知道browser进程中很重要的一个函数就是CreateBrowser，cefsimple这个demo中，使用在了OnContextInitialized函数中，这说明，当cef上下文初始化完成之后就可以创建浏览功能了。

void SimpleApp::OnContextInitialized() {
  CEF_REQUIRE_UI_THREAD();

  CefRefPtr<CefCommandLine> command_line =
      CefCommandLine::GetGlobalCommandLine();

#if defined(OS_WIN) || defined(OS_LINUX)
  // Create the browser using the Views framework if "--use-views" is specified
  // via the command-line. Otherwise, create the browser using the native
  // platform framework. The Views framework is currently only supported on
  // Windows and Linux.
  const bool use_views = command_line->HasSwitch("use-views");
#else
  const bool use_views = false;
#endif

  // SimpleHandler implements browser-level callbacks.
  CefRefPtr<SimpleHandler> handler(new SimpleHandler(use_views));

  // Specify CEF browser settings here.
  CefBrowserSettings browser_settings;

  std::string url;

  // Check if a "--url=" value was provided via the command-line. If so, use
  // that instead of the default URL.
  url = command_line->GetSwitchValue("url");
  if (url.empty())
    url = "http://www.google.com";

  if (use_views) {
    // Create the BrowserView.
    CefRefPtr<CefBrowserView> browser_view = CefBrowserView::CreateBrowserView(
        handler, url, browser_settings, NULL, NULL, NULL);

    // Create the Window. It will show itself after creation.
    CefWindow::CreateTopLevelWindow(new SimpleWindowDelegate(browser_view));
  } else {
    // Information used when creating the native window.
    CefWindowInfo window_info;

#if defined(OS_WIN)
    // On Windows we need to specify certain flags that will be passed to
    // CreateWindowEx().
    window_info.SetAsPopup(NULL, "cefsimple");
#endif

    // Create the first browser window.
    CefBrowserHost::CreateBrowser(window_info, handler, url, browser_settings,
                                  NULL, NULL);
  }
}

而对应的ShutdownBrowser则是在CefContext::Shutdown()中被调用。并不需要开发者过多操作。