Chrome代碼筆記 1 -- Chrome的啓動 II

Chrome.exe通過MainDllLoader加載chrome.dll，然後獲取chrome.dll中的ChromeMain函數指針開始運行chrome.dll中的代碼：

DLLEXPORT int __cdecl ChromeMain(HINSTANCE instance,
                                 sandbox::SandboxInterfaceInfo* sandbox_info) {
  ChromeMainDelegate chrome_main_delegate;
  return content::ContentMain(instance, sandbox_info, &chrome_main_delegate);
}

ChromeMain這個函數在chrome\app\chrome_main.cc中。

這裏，它直接調用了content.dll中的content::ContentMain函數（見content\app\content_main.cc）：

int ContentMain(HINSTANCE instance,
                sandbox::SandboxInterfaceInfo* sandbox_info,
                ContentMainDelegate* delegate) {

scoped_ptr<ContentMainRunner> main_runner(ContentMainRunner::Create());

int exit_code;

exit_code = main_runner->Initialize(instance, sandbox_info, delegate);

  if (exit_code >= 0)
    return exit_code;

  exit_code = main_runner->Run();

  main_runner->Shutdown();

  return exit_code;
}

從這個函數中可以看到，所有的工作都是由ContentMainRunner來驅動的，這個類的定義在content\public\app\content_main_runner.h：

// This class is responsible for content initialization, running and shutdown.
class ContentMainRunner {
public:
  virtual ~ContentMainRunner() {}

  // Create a new ContentMainRunner object.
  static ContentMainRunner* Create();

  // Initialize all necessary content state.
  // The |sandbox_info| and |delegate| objects must outlive this class.
  // |sandbox_info| should be initialized using InitializeSandboxInfo from
  // content_main_win.h.
  virtual int Initialize(HINSTANCE instance,
                         sandbox::SandboxInterfaceInfo* sandbox_info,
                         ContentMainDelegate* delegate) = 0;

  // Perform the default run logic.
  virtual int Run() = 0;

  // Shut down the content state.
  virtual void Shutdown() = 0;
};

ContentMainRunner有以下特點：

1. 它是用來初始化、運行並關閉content的；

2. 它是抽象類；

3. 只能通過Create這個靜態成員函數來獲得一個ContentMainRunner類型的對象；

4. Initialize的註釋中提到，sandbox_info和delegate這兩個對象必須要比ContentMainRunner對象活得長，sandbox_info必須用content_main_win.h中的InitializeSandboxInfo初始化。

另外，在content::ContentMain中第五行有這樣一句：

scoped_ptr<ContentMainRunner> main_runner(ContentMainRunner::Create());

scoped_ptr是一個智能指針，main_runner是這個函數的局部變量，它裏面保存了ContentMainRunner的指針，當這個scope結束的時候，main_runner會被銷燬，同時指針所指向的內容也會被釋放。

Chrome的啓動就先寫到這裏，下次的文章會先介紹ContentMainRunner。