chromium之MessagePump.h

上代码，注释已经写得很详细了。

粗看一下，这是个纯虚类，用于跨平台的通用接口。

MessagePump，Pump的意思是泵，，MessagePump也就是消息泵，输送消息

namespace base {

class Time;

class MessagePump : public RefCountedThreadSafe<MessagePump> {

 public:

  // Please see the comments above the Run method for an illustration of how

  // these delegate methods are used.

  class Delegate {

   public:

    virtual ~Delegate() {}

    // Called from within Run in response to ScheduleWork or when the message

    // pump would otherwise call DoDelayedWork.  Returns true to indicate that

    // work was done.  DoDelayedWork will not be called if DoWork returns true.

    virtual bool DoWork() = ;

    // Called from within Run in response to ScheduleDelayedWork or when the

    // message pump would otherwise sleep waiting for more work.  Returns true

    // to indicate that delayed work was done.  DoIdleWork will not be called

    // if DoDelayedWork returns true.  Upon return |next_delayed_work_time|

    // indicates the time when DoDelayedWork should be called again.  If

    // |next_delayed_work_time| is null (per Time::is_null), then the queue of

    // future delayed work (timer events) is currently empty, and no additional

    // calls to this function need to be scheduled.

    virtual bool DoDelayedWork(Time* next_delayed_work_time) = ;

    // Called from within Run just before the message pump goes to sleep.

    // Returns true to indicate that idle work was done.

    virtual bool DoIdleWork() = ;

  };

  virtual ~MessagePump() {}

  // The Run method is called to enter the message pump's run loop.

  //

  // Within the method, the message pump is responsible for processing native

  // messages as well as for giving cycles to the delegate periodically.  The

  // message pump should take care to mix delegate callbacks with native

  // message processing so neither type of event starves the other of cycles.

  //

  // The anatomy of a typical run loop:

  //

  //   for (;;) {

  //     bool did_work = DoInternalWork();

  //     if (should_quit_)

  //       break;

  //

  //     did_work |= delegate_->DoWork();

  //     if (should_quit_)

  //       break;

  //

  //     did_work |= delegate_->DoDelayedWork();

  //     if (should_quit_)

  //       break;

  //

  //     if (did_work)

  //       continue;

  //

  //     did_work = delegate_->DoIdleWork();

  //     if (should_quit_)

  //       break;

  //

  //     if (did_work)

  //       continue;

  //

  //     WaitForWork();

  //   }

  //

  // Here, DoInternalWork is some private method of the message pump that is

  // responsible for dispatching the next UI message or notifying the next IO

  // completion (for example).  WaitForWork is a private method that simply

  // blocks until there is more work of any type to do.

  //

  // Notice that the run loop cycles between calling DoInternalWork, DoWork,

  // and DoDelayedWork methods.  This helps ensure that neither work queue

  // starves the other.  This is important for message pumps that are used to

  // drive animations, for example.

  //

  // Notice also that after each callout to foreign code, the run loop checks

  // to see if it should quit.  The Quit method is responsible for setting this

  // flag.  No further work is done once the quit flag is set.

  //

  // NOTE: Care must be taken to handle Run being called again from within any

  // of the callouts to foreign code.  Native message pumps may also need to

  // deal with other native message pumps being run outside their control

  // (e.g., the MessageBox API on Windows pumps UI messages!).  To be specific,

  // the callouts (DoWork and DoDelayedWork) MUST still be provided even in

  // nested sub-loops that are "seemingly" outside the control of this message

  // pump.  DoWork in particular must never be starved for time slices unless

  // it returns false (meaning it has run out of things to do).

  //

  virtual void Run(Delegate* delegate) = ;

  // Quit immediately from the most recently entered run loop.  This method may

  // only be used on the thread that called Run.

  virtual void Quit() = ;

  // Schedule a DoWork callback to happen reasonably soon.  Does nothing if a

  // DoWork callback is already scheduled.  This method may be called from any

  // thread.  Once this call is made, DoWork should not be "starved" at least

  // until it returns a value of false.

  virtual void ScheduleWork() = ;

  // Schedule a DoDelayedWork callback to happen at the specified time,

  // cancelling any pending DoDelayedWork callback.  This method may only be

  // used on the thread that called Run.

  virtual void ScheduleDelayedWork(const Time& delayed_work_time) = ;

};

}  // namespace base