Chrome源代码分析之single process 模式分析(十七)

如果选择了单进程模式，那么只需要建立一个renderer线程即可，同时为这个线程搭建ipc功能，虽然同一个进程，renderer与browser之间仍然通过ipc通信，这样多进程和单进程的通信方法统一在一起了。各种IPC消息的映射代码不需要做任何改动。

代码如下：

    // Crank up a thread and run the initialization there.  With the way that
    // messages flow between the browser and renderer, this thread is required
    // to prevent a deadlock in single-process mode.  Since the primordial
    // thread in the renderer process runs the WebKit code and can sometimes
    // make blocking calls to the UI thread (i.e. this thread), they need to run
    // on separate threads.
    in_process_renderer_.reset(new RendererMainThread(channel_id));


    base::Thread::Options options;
#if !defined(TOOLKIT_USES_GTK)
    // In-process plugins require this to be a UI message loop.
    options.message_loop_type = MessageLoop::TYPE_UI;
#else
    // We can't have multiple UI loops on GTK, so we don't support
    // in-process plugins.
    options.message_loop_type = MessageLoop::TYPE_DEFAULT;
#endif
    in_process_renderer_->StartWithOptions(options);


    OnProcessLaunched();  // Fake a callback that the process is ready.

这里定义个了一个in_process_renderer_代表整个render，RendererMainThread是Thread的子类，RendererMainThread中也有一个RenderProcessImpl类的对象，RenderProcessImpl跟多进程模式下一样有一个main_thread_和io_thread_对象，main_thread_就是前面定义的RendererMainThread线程，后面即会调用n_process_renderer_->StartWithOptions(options);启动这个线程。

RendererMainThread的nit()函数代码如下：

  virtual void Init() {
#if defined(OS_WIN)
    CoInitialize(NULL);
#endif


    render_process_ = new RenderProcessImpl();
    render_process_->set_main_thread(new RenderThread(channel_id_));
    // It's a little lame to manually set this flag.  But the single process
    // RendererThread will receive the WM_QUIT.  We don't need to assert on
    // this thread, so just force the flag manually.
    // If we want to avoid this, we could create the InProcRendererThread
    // directly with _beginthreadex() rather than using the Thread class.
    base::Thread::SetThreadWasQuitProperly(true);
  }


  virtual void CleanUp() {
    delete render_process_;


#if defined(OS_WIN)
    CoUninitialize();
#endif
  }

这里面会新建RenderProcessImpl的对象，如同多进程模式一样，ipc对象和io线程随后会在RenderThread和RenderProcessImpl的构造函数中被创建和初始化。