michael@0: // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_WAITABLE_EVENT_WATCHER_H_
michael@0: #define BASE_WAITABLE_EVENT_WATCHER_H_
michael@0: 
michael@0: #include "build/build_config.h"
michael@0: 
michael@0: #if defined(OS_WIN)
michael@0: #include "base/object_watcher.h"
michael@0: #else
michael@0: #include "base/message_loop.h"
michael@0: #include "base/waitable_event.h"
michael@0: #endif
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: class Flag;
michael@0: class AsyncWaiter;
michael@0: class AsyncCallbackTask;
michael@0: class WaitableEvent;
michael@0: 
michael@0: // -----------------------------------------------------------------------------
michael@0: // This class provides a way to wait on a WaitableEvent asynchronously.
michael@0: //
michael@0: // Each instance of this object can be waiting on a single WaitableEvent. When
michael@0: // the waitable event is signaled, a callback is made in the thread of a given
michael@0: // MessageLoop. This callback can be deleted by deleting the waiter.
michael@0: //
michael@0: // Typical usage:
michael@0: //
michael@0: //   class MyClass : public base::WaitableEventWatcher::Delegate {
michael@0: //    public:
michael@0: //     void DoStuffWhenSignaled(WaitableEvent *waitable_event) {
michael@0: //       watcher_.StartWatching(waitable_event, this);
michael@0: //     }
michael@0: //     virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) {
michael@0: //       // OK, time to do stuff!
michael@0: //     }
michael@0: //    private:
michael@0: //     base::WaitableEventWatcher watcher_;
michael@0: //   };
michael@0: //
michael@0: // In the above example, MyClass wants to "do stuff" when waitable_event
michael@0: // becomes signaled. WaitableEventWatcher makes this task easy. When MyClass
michael@0: // goes out of scope, the watcher_ will be destroyed, and there is no need to
michael@0: // worry about OnWaitableEventSignaled being called on a deleted MyClass
michael@0: // pointer.
michael@0: //
michael@0: // BEWARE: With automatically reset WaitableEvents, a signal may be lost if it
michael@0: // occurs just before a WaitableEventWatcher is deleted. There is currently no
michael@0: // safe way to stop watching an automatic reset WaitableEvent without possibly
michael@0: // missing a signal.
michael@0: //
michael@0: // NOTE: you /are/ allowed to delete the WaitableEvent while still waiting on
michael@0: // it with a Watcher. It will act as if the event was never signaled.
michael@0: // -----------------------------------------------------------------------------
michael@0: 
michael@0: class WaitableEventWatcher
michael@0: #if defined(OS_POSIX)
michael@0:     : public MessageLoop::DestructionObserver
michael@0: #endif
michael@0: {
michael@0:  public:
michael@0: 
michael@0:   WaitableEventWatcher();
michael@0:   ~WaitableEventWatcher();
michael@0: 
michael@0:   class Delegate {
michael@0:    public:
michael@0:     virtual ~Delegate() { }
michael@0: 
michael@0:     // -------------------------------------------------------------------------
michael@0:     // This is called on the MessageLoop thread when WaitableEvent has been
michael@0:     // signaled.
michael@0:     //
michael@0:     // Note: the event may not be signaled by the time that this function is
michael@0:     // called. This indicates only that it has been signaled at some point in
michael@0:     // the past.
michael@0:     // -------------------------------------------------------------------------
michael@0:     virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) = 0;
michael@0:   };
michael@0: 
michael@0:   // ---------------------------------------------------------------------------
michael@0:   // When @event is signaled, the given delegate is called on the thread of the
michael@0:   // current message loop when StartWatching is called. The delegate is not
michael@0:   // deleted.
michael@0:   // ---------------------------------------------------------------------------
michael@0:   bool StartWatching(WaitableEvent* event, Delegate* delegate);
michael@0: 
michael@0:   // ---------------------------------------------------------------------------
michael@0:   // Cancel the current watch. Must be called from the same thread which
michael@0:   // started the watch.
michael@0:   //
michael@0:   // Does nothing if no event is being watched, nor if the watch has completed.
michael@0:   // The delegate will *not* be called for the current watch after this
michael@0:   // function returns. Since the delegate runs on the same thread as this
michael@0:   // function, it cannot be called during this function either.
michael@0:   // ---------------------------------------------------------------------------
michael@0:   void StopWatching();
michael@0: 
michael@0:   // ---------------------------------------------------------------------------
michael@0:   // Return the currently watched event, or NULL if no object is currently being
michael@0:   // watched.
michael@0:   // ---------------------------------------------------------------------------
michael@0:   WaitableEvent* GetWatchedEvent();
michael@0: 
michael@0:  private:
michael@0:   WaitableEvent* event_;
michael@0: 
michael@0: #if defined(OS_WIN)
michael@0:   // ---------------------------------------------------------------------------
michael@0:   // The helper class exists because, if WaitableEventWatcher were to inherit
michael@0:   // from ObjectWatcher::Delegate, then it couldn't also have an inner class
michael@0:   // called Delegate (at least on Windows). Thus this object exists to proxy
michael@0:   // the callback function
michael@0:   // ---------------------------------------------------------------------------
michael@0:   class ObjectWatcherHelper : public ObjectWatcher::Delegate {
michael@0:    public:
michael@0:     ObjectWatcherHelper(WaitableEventWatcher* watcher);
michael@0: 
michael@0:     // -------------------------------------------------------------------------
michael@0:     // Implementation of ObjectWatcher::Delegate
michael@0:     // -------------------------------------------------------------------------
michael@0:     void OnObjectSignaled(HANDLE h);
michael@0: 
michael@0:    private:
michael@0:     WaitableEventWatcher *const watcher_;
michael@0:   };
michael@0: 
michael@0:   void OnObjectSignaled();
michael@0: 
michael@0:   Delegate* delegate_;
michael@0:   ObjectWatcherHelper helper_;
michael@0:   ObjectWatcher watcher_;
michael@0: #else
michael@0:   // ---------------------------------------------------------------------------
michael@0:   // Implementation of MessageLoop::DestructionObserver
michael@0:   // ---------------------------------------------------------------------------
michael@0:   void WillDestroyCurrentMessageLoop();
michael@0: 
michael@0:   MessageLoop* message_loop_;
michael@0:   scoped_refptr<Flag> cancel_flag_;
michael@0:   AsyncWaiter* waiter_;
michael@0:   AsyncCallbackTask* callback_task_;
michael@0:   scoped_refptr<WaitableEvent::WaitableEventKernel> kernel_;
michael@0: #endif
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_WAITABLE_EVENT_WATCHER_H_