CEF关闭流程

原文链接：https://github.com/fanfeilong/cefutil/blob/master/doc/CEF_Close.md

我来说windows下CEF3.2171的关闭流程，里面会引用一部分官方库的文档和个人的伪代码，为了辅助理解—— 以下是截取自cef_life_span_handler.h的头文件文档，所以一部分文档他还是写在头文件里的，根据他的流程，能很快的去梳理相关逻辑

  // The CefLifeSpanHandler::OnBeforeClose() method will be called immediately  // before the browser object is destroyed. The application should only exit  // after OnBeforeClose() has been called for all existing browsers.  //  // If the browser represents a modal window and a custom modal loop  // implementation was provided in CefLifeSpanHandler::RunModal() this callback  // should be used to restore the opener window to a usable state.  //  // By way of example consider what should happen during window close when the  // browser is parented to an application-provided top-level OS window.  // 1.  User clicks the window close button which sends an OS close  //     notification (e.g. WM_CLOSE on Windows, performClose: on OS-X and  //     "delete_event" on Linux).  // 2.  Application's top-level window receives the close notification and:  //     A. Calls CefBrowserHost::CloseBrowser(false).  //     B. Cancels the window close.  // 3.  JavaScript 'onbeforeunload' handler executes and shows the close  //     confirmation dialog (which can be overridden via  //     CefJSDialogHandler::OnBeforeUnloadDialog()).  // 4.  User approves the close.  // 5.  JavaScript 'onunload' handler executes.  // 6.  Application's DoClose() handler is called. Application will:  //     A. Set a flag to indicate that the next close attempt will be allowed.  //     B. Return false.  // 7.  CEF sends an OS close notification.  // 8.  Application's top-level window receives the OS close notification and  //     allows the window to close based on the flag from #6B.  // 9.  Browser OS window is destroyed.  // 10. Application's CefLifeSpanHandler::OnBeforeClose() handler is called and  //     the browser object is destroyed.  // 11. Application exits by calling CefQuitMessageLoop() if no other browsers  //     exist.

pre1. 如果你要管理CefBrowser的生命周期，意味者你必须实现相关 CefLifeSpanHandler接口，在OnAfterCreated里管理和获取CefBrowser的每一个browser，在DoClose和OnBeforeClose里管理关闭 pre2. 这里要注意整个流程对应开发者来说不是线性代码，都是基于消息、事件投递、接口切面的一种编程习惯，大家要对异步接口的开发有心理准备，你实现的一个接口都是等待框架或者别人调用。

1. 用户发起了一个系统级别的关闭操作，比如CLOSE，window下会被WM_CLOSE和相关封装触发
2. 系统的顶层窗口消息处理会获取到CLOSE消息   A. 调用 CefBrowserHost::CloseBrowser(false), 通知HOST开始关闭流程，参数force_close=false，我们不需要交互式关闭。   B. 取消系统级关闭，比如以下代码我"return 0; "拒接了系统窗口的关闭流程，进入了个人和CEF的流程

     case WM_CLOSE:      if (client && !client->IsClosing()) {        CefRefPtr<CefBrowser> browser = client->GetBrowser();        if (browser.get()) {          // Notify the browser window that we would like to close it. This          // will result in a call to ClientHandler::DoClose() if the          // JavaScript 'onbeforeunload' event handler allows it.          browser->GetHost()->CloseBrowser(false);          // Cancel the close.          return 0;        }      }      // Allow the close.      break;

这是单browser关闭

browser->GetHost()->CloseBrowser(false);

同样可以替换成多browser关闭

void ClientHandler::CloseAllBrowsers(bool force_close) {  if (!CefCurrentlyOn(TID_UI)) {    // Execute on the UI thread.    CefPostTask(TID_UI,        base::Bind(&ClientHandler::CloseAllBrowsers, this, force_close));    return;  }  if (!popup_browsers_.empty()) {    // Request that any popup browsers close.    BrowserList::const_iterator it = popup_browsers_.begin();    for (; it != popup_browsers_.end(); ++it)      (*it)->GetHost()->CloseBrowser(force_close);  }  if (browser_.get()) {    // Request that the main browser close.    browser_->GetHost()->CloseBrowser(force_close);  }}

intermittent. 最终会触发一个或多个CloseBrowser => CefBrowserHostImpl::CloseBrowser => CefBrowserHostImpl::CloseContents

void CefBrowserHostImpl::CloseBrowser(bool force_close) {  if (CEF_CURRENTLY_ON_UIT()) {    // Exit early if a close attempt is already pending and this method is    // called again from somewhere other than WindowDestroyed().    if (destruction_state_ >= DESTRUCTION_STATE_PENDING &&        (IsWindowless() || !window_destroyed_)) {      if (force_close && destruction_state_ == DESTRUCTION_STATE_PENDING) {        // Upgrade the destruction state.        destruction_state_ = DESTRUCTION_STATE_ACCEPTED;      }      return;    }    if (destruction_state_ < DESTRUCTION_STATE_ACCEPTED) {      destruction_state_ = (force_close ? DESTRUCTION_STATE_ACCEPTED :                                          DESTRUCTION_STATE_PENDING);    }    content::WebContents* contents = web_contents();    if (contents && contents->NeedToFireBeforeUnload()) {      // Will result in a call to BeforeUnloadFired() and, if the close isn't      // canceled, CloseContents().      contents->DispatchBeforeUnload(false);    } else {      CloseContents(contents);    }  } else {    CEF_POST_TASK(CEF_UIT,        base::Bind(&CefBrowserHostImpl::CloseBrowser, this, force_close));  }}

我们跳过其他细节（ 我也没关注:) ），和相关CEF_POST_TASK把函数投递到UI线程上去处理的线程类型,最后会进入 CloseContents

void CefBrowserHostImpl::CloseContents(content::WebContents* source) {  if (destruction_state_ == DESTRUCTION_STATE_COMPLETED)    return;  bool close_browser = true;  // If this method is called in response to something other than  // WindowDestroyed() ask the user if the browser should close.  if (client_.get() && (IsWindowless() || !window_destroyed_)) {    CefRefPtr<CefLifeSpanHandler> handler =        client_->GetLifeSpanHandler();    if (handler.get()) {      close_browser = !handler->DoClose(this);   // CefLifeSpanHandler::DoClose    }  }  if (close_browser) {    if (destruction_state_ != DESTRUCTION_STATE_ACCEPTED)      destruction_state_ = DESTRUCTION_STATE_ACCEPTED;    if (!IsWindowless() && !window_destroyed_) {      // A window exists so try to close it using the platform method. Will      // result in a call to WindowDestroyed() if/when the window is destroyed      // via the platform window destruction mechanism.      PlatformCloseWindow();    } else {      // Keep a reference to the browser while it's in the process of being      // destroyed.      CefRefPtr<CefBrowserHostImpl> browser(this);      // No window exists. Destroy the browser immediately.      DestroyBrowser();       // CefLifeSpanHandler::OnBeforeClose      if (!IsWindowless()) {        // Release the reference added in PlatformCreateWindow().        Release();      }    }  } else if (destruction_state_ != DESTRUCTION_STATE_NONE) {    destruction_state_ = DESTRUCTION_STATE_NONE;  }}

在CloseContents里发现了我们的DoClose接口，其实这个函数里还有我们要处理的OnBeforeClose接口，DestroyBrowser包含了他

void CefBrowserHostImpl::DestroyBrowser() {  CEF_REQUIRE_UIT();  destruction_state_ = DESTRUCTION_STATE_COMPLETED;  if (client_.get()) {    CefRefPtr<CefLifeSpanHandler> handler = client_->GetLifeSpanHandler();    if (handler.get()) {      // Notify the handler that the window is about to be closed.      handler->OnBeforeClose(this);        //`CefLifeSpanHandler::OnBeforeClose    }  }  // 省略}

到这里我们要有这样的调用栈初步概念（之后会修改..)

=> 表示同步调用 ->异步调用[os]window close =>    [个人]browser(s) close =>        [cef]CefBrowserHostImpl::CloseBrowser =>            [cef]CefBrowserHostImpl::CloseContents =>                [实现cef接口]CefLifeSpanHandler::DoClose =>                [cef]CefLifeSpanHandler::DestroyBrowser =>                    [实现cef接口]CefLifeSpanHandler::OnBeforeClose =>[os]阻止window close

3-5. js和交互级的操作，略，其中有一点js onunload让你有机会在js层面去通知关闭，比如通知后台的native 线程去做自我清理动作，特别是cefQuery持久化以后的和JS交互的native线程 6.DoClose接口被调用   A. 允许设置一些状态表示browser正在关闭   B. "return false;" 我们不需要紧急关闭（好像是预留接口，或者其他平台用) 7.cef 发送一个系统级别的关闭动作发现之前的调用栈已经需要修改了，因为这里异步操作) CloseContents => PlatformCloseWindow => CefBrowserHostImpl::PlatformCloseWindow =>PostMessage WM_CLOSE

void CefBrowserHostImpl::PlatformCloseWindow() {  if (window_info_.window != NULL) {    HWND frameWnd = GetAncestor(window_info_.window, GA_ROOT);    PostMessage(frameWnd, WM_CLOSE, 0, 0);  }}

PS: host公共代码在这个文件browser_host_impl.cc里，平台特殊接口在browser_host_impl_xxx.cc里 PlatformCloseWindow在browser_host_impl_win.cc里

允许关闭"if (client && !client->IsClosing()) " 之前我代码里IsClosing已经允许（

 case WM_CLOSE:      if (client && !client->IsClosing()) {// 这次不会进入IF分支

8.系统窗口已销毁

LRESULT CALLBACK CefBrowserHostImpl::WndProc(HWND hwnd, UINT message,                                             WPARAM wParam, LPARAM lParam) {// 略  case WM_DESTROY:    if (browser) {      // Clear the user data pointer.      gfx::SetWindowUserData(hwnd, NULL);      // Force the browser to be destroyed and release the reference added in      // PlatformCreateWindow().      browser->WindowDestroyed();    }    return 0;// 略  }

cef竟然在等系统群发销毁消息然后处理的代码，看到这里才发现CefBrowserHostImpl这个类是CefBrowser和系统整合的桥梁，不同平台对 CefBrowserHostImpl 的实现也不一样

9.框架发起销毁操作 10. 调用OnBeforeClose WM_DESTROY => CefBrowserHostImpl::WindowDestroyed => ClientHandler::OnBeforeClose

void ClientHandler::OnBeforeClose(CefRefPtr<CefBrowser> browser) {  CEF_REQUIRE_UI_THREAD();  message_router_->OnBeforeClose(browser);  if (GetBrowserId() == browser->GetIdentifier()) {    {      base::AutoLock lock_scope(lock_);      // Free the browser pointer so that the browser can be destroyed      browser_ = NULL;    }    if (osr_handler_.get()) {      osr_handler_->OnBeforeClose(browser);      osr_handler_ = NULL;    }  } else if (browser->IsPopup()) {    // Remove from the browser popup list.    BrowserList::iterator bit = popup_browsers_.begin();    for (; bit != popup_browsers_.end(); ++bit) {      if ((*bit)->IsSame(browser)) {        popup_browsers_.erase(bit);        break;      }    }  }  if (--browser_count_ == 0) {    // All browser windows have closed.    // Remove and delete message router handlers.    MessageHandlerSet::const_iterator it = message_handler_set_.begin();    for (; it != message_handler_set_.end(); ++it) {      message_router_->RemoveHandler(*(it));      delete *(it);    }    message_handler_set_.clear();    message_router_ = NULL;    // Quit the application message loop.    //AppQuitMessageLoop();  XCefAppManage::Instance()->QuitMessageLoop();  }}

我判断到 "--browser_count_ == 0" , 开始发起真实关闭。

11. 发起的真实关闭逻辑 个人在OnBeforeClose里销毁所有browser和相关操作cefquery组件销毁以后，发起了总的关闭流程（关闭是异步的）

void            XCefAppManage::QuitMessageLoop() {  if (GetCefSettings().multi_threaded_message_loop)  {    // Running in multi-threaded message loop mode. Need to execute    // PostQuitMessage on the main application thread.    if (NULL == message_wnd__)    {      message_wnd__ = ::FindWindow(XWinUtil::GetMessageWindowClassName(XWinUtil::GetParentProcessID()), NULL);    }    DCHECK(message_wnd__);    PostMessage(message_wnd__, WM_COMMAND, ID_QUIT, 0);  }  else {    CefQuitMessageLoop();  }}

如果CefRunMessageLoop创建的消息循环对应CefQuitMessageLoop去终结，其他方式的处理就千奇百怪了，我根据cefclient的例子用一个隐藏窗口来结束系统的消息循环

PostMessage(message_wnd__, WM_COMMAND, ID_QUIT, 0);

处理非常简单，调用了原生API PostQuitMessage退出循环

    case ID_QUIT:      PostQuitMessage(0);      return 0;

PS: 如果需要把CEF混入其他框架的话，不同框架的处理都需要适配，切记。 12. CefShutDown() 销毁Cef资源，如果有资源没关闭，比如browser的计数不为0，debug下会check assert。 最后我再来修改一下之前的调用栈

=> 表示同步调用 ->异步调用[os]on window close WM_CLOSE =>    [个人]browser(s) close =>        [cef]CefBrowserHostImpl::CloseBrowser =>            [cef]CefBrowserHostImpl::CloseContents =>                [实现cef接口]CefLifeSpanHandler::DoClose =>                [cef]CefBrowserHostImpl::PlatformCloseWindow =>                    [os] post window close -> WM_CLOSE[os]阻止window closepost被接收[os] 第二次on window close WM_CLOSE =>     [个人] 允许 window close ->WM_DESTROY[os] 系统群发WM_DESTROY    [cef] CefBrowserHostImpl::WndProc =>        [cef & os] 每个browser proc内的 WM_CLOSE 处理        [cef]CefLifeSpanHandler::DestroyBrowser =>            [实现cef接口]CefLifeSpanHandler::OnBeforeClose =>                发起总关闭(个人使用XCefAppManage::QuitMessageLoop)->退出消息循环CefShutDown