// Copyright (c) 2011 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_WIN_OBJECT_WATCHER_H_
#define BASE_WIN_OBJECT_WATCHER_H_
#include <windows.h>
#include "base/base_export.h"
#include "base/callback.h"
#include "base/memory/weak_ptr.h"
#include "base/message_loop/message_loop.h"
namespace base {
namespace win {
// A class that provides a means to asynchronously wait for a Windows object to
// become signaled. It is an abstraction around RegisterWaitForSingleObject
// that provides a notification callback, OnObjectSignaled, that runs back on
// the origin thread (i.e., the thread that called StartWatching).
//
// This class acts like a smart pointer such that when it goes out-of-scope,
// UnregisterWaitEx is automatically called, and any in-flight notification is
// suppressed.
//
// Typical usage:
//
// class MyClass : public base::ObjectWatcher::Delegate {
// public:
// void DoStuffWhenSignaled(HANDLE object) {
// watcher_.StartWatching(object, this);
// }
// virtual void OnObjectSignaled(HANDLE object) {
// // OK, time to do stuff!
// }
// private:
// base::ObjectWatcher watcher_;
// };
//
// In the above example, MyClass wants to "do stuff" when object becomes
// signaled. ObjectWatcher makes this task easy. When MyClass goes out of
// scope, the watcher_ will be destroyed, and there is no need to worry about
// OnObjectSignaled being called on a deleted MyClass pointer. Easy!
// If the object is already signaled before being watched, OnObjectSignaled is
// still called after (but not necessarily immediately after) watch is started.
//
class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver {
public:
class BASE_EXPORT Delegate {
public:
virtual ~Delegate() {}
// Called from the MessageLoop when a signaled object is detected. To
// continue watching the object, StartWatching must be called again.
virtual void OnObjectSignaled(HANDLE object) = 0;
};
ObjectWatcher();
~ObjectWatcher();
// When the object is signaled, the given delegate is notified on the thread
// where StartWatching is called. The ObjectWatcher is not responsible for
// deleting the delegate.
//
// Returns true if the watch was started. Otherwise, false is returned.
//
bool StartWatching(HANDLE object, Delegate* delegate);
// Stops watching. Does nothing if the watch has already completed. If the
// watch is still active, then it is canceled, and the associated delegate is
// not notified.
//
// Returns true if the watch was canceled. Otherwise, false is returned.
//
bool StopWatching();
// Returns the handle of the object being watched, or NULL if the object
// watcher is stopped.
HANDLE GetWatchedObject();
private:
// Called on a background thread when done waiting.
static void CALLBACK DoneWaiting(void* param, BOOLEAN timed_out);
void Signal(Delegate* delegate);
// MessageLoop::DestructionObserver implementation:
virtual void WillDestroyCurrentMessageLoop();
// Internal state.
WeakPtrFactory<ObjectWatcher> weak_factory_;
Closure callback_;
HANDLE object_; // The object being watched
HANDLE wait_object_; // Returned by RegisterWaitForSingleObject
MessageLoop* origin_loop_; // Used to get back to the origin thread
DISALLOW_COPY_AND_ASSIGN(ObjectWatcher);
};
} // namespace win
} // namespace base
#endif // BASE_OBJECT_WATCHER_H_