The Tor Browser / file revision

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 #ifndef BASE_WAITABLE_EVENT_WATCHER_H_

 #define BASE_WAITABLE_EVENT_WATCHER_H_

 #include "build/build_config.h"

 #if defined(OS_WIN)

 #include "base/object_watcher.h"

 #else

 #include "base/message_loop.h"

 #include "base/waitable_event.h"

 #endif

 namespace base {

 class Flag;

 class AsyncWaiter;

 class AsyncCallbackTask;

 class WaitableEvent;

 // -----------------------------------------------------------------------------

 // This class provides a way to wait on a WaitableEvent asynchronously.

 //

 // Each instance of this object can be waiting on a single WaitableEvent. When

 // the waitable event is signaled, a callback is made in the thread of a given

 // MessageLoop. This callback can be deleted by deleting the waiter.

 //

 // Typical usage:

 //

 //   class MyClass : public base::WaitableEventWatcher::Delegate {

 //    public:

 //     void DoStuffWhenSignaled(WaitableEvent *waitable_event) {

 //       watcher_.StartWatching(waitable_event, this);

 //     }

 //     virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) {

 //       // OK, time to do stuff!

 //     }

 //    private:

 //     base::WaitableEventWatcher watcher_;

 //   };

 //

 // In the above example, MyClass wants to "do stuff" when waitable_event

 // becomes signaled. WaitableEventWatcher makes this task easy. When MyClass

 // goes out of scope, the watcher_ will be destroyed, and there is no need to

 // worry about OnWaitableEventSignaled being called on a deleted MyClass

 // pointer.

 //

 // BEWARE: With automatically reset WaitableEvents, a signal may be lost if it

 // occurs just before a WaitableEventWatcher is deleted. There is currently no

 // safe way to stop watching an automatic reset WaitableEvent without possibly

 // missing a signal.

 //

 // NOTE: you /are/ allowed to delete the WaitableEvent while still waiting on

 // it with a Watcher. It will act as if the event was never signaled.

 // -----------------------------------------------------------------------------

 class WaitableEventWatcher

 #if defined(OS_POSIX)

     : public MessageLoop::DestructionObserver

 #endif

 {

  public:

   WaitableEventWatcher();

   ~WaitableEventWatcher();

   class Delegate {

    public:

     virtual ~Delegate() { }

     // -------------------------------------------------------------------------

     // This is called on the MessageLoop thread when WaitableEvent has been

     // signaled.

     //

     // Note: the event may not be signaled by the time that this function is

     // called. This indicates only that it has been signaled at some point in

     // the past.

     // -------------------------------------------------------------------------

     virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) = 0;

   };

   // ---------------------------------------------------------------------------

   // When @event is signaled, the given delegate is called on the thread of the

   // current message loop when StartWatching is called. The delegate is not

   // deleted.

   // ---------------------------------------------------------------------------

   bool StartWatching(WaitableEvent* event, Delegate* delegate);

   // ---------------------------------------------------------------------------

   // Cancel the current watch. Must be called from the same thread which

   // started the watch.

   //

   // Does nothing if no event is being watched, nor if the watch has completed.

   // The delegate will *not* be called for the current watch after this

   // function returns. Since the delegate runs on the same thread as this

   // function, it cannot be called during this function either.

   // ---------------------------------------------------------------------------

   void StopWatching();

   // ---------------------------------------------------------------------------

   // Return the currently watched event, or NULL if no object is currently being

   // watched.

   // ---------------------------------------------------------------------------

   WaitableEvent* GetWatchedEvent();

  private:

   WaitableEvent* event_;

 #if defined(OS_WIN)

   // ---------------------------------------------------------------------------

   // The helper class exists because, if WaitableEventWatcher were to inherit

   // from ObjectWatcher::Delegate, then it couldn't also have an inner class

   // called Delegate (at least on Windows). Thus this object exists to proxy

   // the callback function

   // ---------------------------------------------------------------------------

   class ObjectWatcherHelper : public ObjectWatcher::Delegate {

    public:

     ObjectWatcherHelper(WaitableEventWatcher* watcher);

     // -------------------------------------------------------------------------

     // Implementation of ObjectWatcher::Delegate

     // -------------------------------------------------------------------------

     void OnObjectSignaled(HANDLE h);

    private:

     WaitableEventWatcher *const watcher_;

   };

   void OnObjectSignaled();

   Delegate* delegate_;

   ObjectWatcherHelper helper_;

   ObjectWatcher watcher_;

 #else

   // ---------------------------------------------------------------------------

   // Implementation of MessageLoop::DestructionObserver

   // ---------------------------------------------------------------------------

   void WillDestroyCurrentMessageLoop();

   MessageLoop* message_loop_;

   scoped_refptr<Flag> cancel_flag_;

   AsyncWaiter* waiter_;

   AsyncCallbackTask* callback_task_;

   scoped_refptr<WaitableEvent::WaitableEventKernel> kernel_;

 #endif

 };

 }  // namespace base

 #endif  // BASE_WAITABLE_EVENT_WATCHER_H_