cef源碼分析之cefsimple

下面是cefsimple的入口代碼，主要分成兩個部分

// 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;
}

進程判斷

首先是初始化進程的代碼，cef的進程結構和chromium類似，都是多進程共用代碼。所以cef提供了一些函數來檢測主進程（即browser進程）的流程和子進程的流程，以分別執行適合當前執行進程的邏輯。這段代碼如下所示。

// 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用於獲取當前進程的命令行參數，因為在chromium中，進程的區分就是靠命令行參數中的--type，如果是browser進程，則沒有--type參數，其他進程該參數的值為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
}

只有當非browser進程時才會執行ContentMain函數，這也符合chromium的邏輯。ContentMain函數是其他子進程的入口點。
而browser進程則會返回執行CefInitialize和CefRunMessageLoop進入browser進程的主循環。當進程需要退出時，CefRunMessageLoop主循環退出，執行CefShutdown進程結束。

cef的browser進程啟動

第二個部分就是browser進程的主流程，下面是拆分出來的代碼。

  // 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初始化函數，其中app.get()即CefApp對象指針的參數尤為重要，在文件libcef/browser/context.cc中，提供了不少類似CefInitialize的cef控制函數，初始化，關閉，開啟和退出消息循環等

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);
}

為的是創建一個全局的CefContext對象，只有當CefContext對象被創建完成后，才能進行CreateBrowser操作，在下面的代碼中

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

Initialize的主要作用是根據content api開始做瀏覽器進程啟動准備。因為content api要涉及chromium代碼，這里就不繼續往下追溯，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的引用會一直傳遞到這里，當初始化的流程結束的時候（OnContextInitialized），就到了CefApp發揮作用的時候了。

其中main_delegate_作為一個代理，主要代理總體管理的相關功能，包括資源初始化，瀏覽器關閉等。那么CefApp對它有什么用呢？主要是為了創建一個全局的CefContentClient對象。

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

然后當CefContext初始化完成后，就會從這個全局的CefContentClient對象中獲取CefApp的引用。而獲得引用之后是為了獲得handler，以完成對應的回調。

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();
  }
}

此處主要獲取的是browser process handler，這個handler的主要目的是監控並觸發browser進程生命周期內各個關鍵時機的回調。

如果多少用過cef，會知道browser進程中很重要的一個函數就是CreateBrowser，cefsimple這個demo中，使用在了OnContextInitialized函數中，這說明，當cef上下文初始化完成之后就可以創建瀏覽功能了。

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);
  }
}

而對應的ShutdownBrowser則是在CefContext::Shutdown()中被調用。並不需要開發者過多操作。