1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_WIN_OBJECT_WATCHER_H_ 6 #define BASE_WIN_OBJECT_WATCHER_H_ 7 8 #include <windows.h> 9 10 #include "base/base_export.h" 11 #include "base/callback.h" 12 #include "base/memory/weak_ptr.h" 13 #include "base/message_loop/message_loop.h" 14 15 namespace base { 16 namespace win { 17 18 // A class that provides a means to asynchronously wait for a Windows object to 19 // become signaled. It is an abstraction around RegisterWaitForSingleObject 20 // that provides a notification callback, OnObjectSignaled, that runs back on 21 // the origin thread (i.e., the thread that called StartWatching). 22 // 23 // This class acts like a smart pointer such that when it goes out-of-scope, 24 // UnregisterWaitEx is automatically called, and any in-flight notification is 25 // suppressed. 26 // 27 // Typical usage: 28 // 29 // class MyClass : public base::ObjectWatcher::Delegate { 30 // public: 31 // void DoStuffWhenSignaled(HANDLE object) { 32 // watcher_.StartWatching(object, this); 33 // } 34 // virtual void OnObjectSignaled(HANDLE object) { 35 // // OK, time to do stuff! 36 // } 37 // private: 38 // base::ObjectWatcher watcher_; 39 // }; 40 // 41 // In the above example, MyClass wants to "do stuff" when object becomes 42 // signaled. ObjectWatcher makes this task easy. When MyClass goes out of 43 // scope, the watcher_ will be destroyed, and there is no need to worry about 44 // OnObjectSignaled being called on a deleted MyClass pointer. Easy! 45 // If the object is already signaled before being watched, OnObjectSignaled is 46 // still called after (but not necessarily immediately after) watch is started. 47 // 48 class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver { 49 public: 50 class BASE_EXPORT Delegate { 51 public: 52 virtual ~Delegate() {} 53 // Called from the MessageLoop when a signaled object is detected. To 54 // continue watching the object, StartWatching must be called again. 55 virtual void OnObjectSignaled(HANDLE object) = 0; 56 }; 57 58 ObjectWatcher(); 59 ~ObjectWatcher(); 60 61 // When the object is signaled, the given delegate is notified on the thread 62 // where StartWatching is called. The ObjectWatcher is not responsible for 63 // deleting the delegate. 64 // 65 // Returns true if the watch was started. Otherwise, false is returned. 66 // 67 bool StartWatching(HANDLE object, Delegate* delegate); 68 69 // Stops watching. Does nothing if the watch has already completed. If the 70 // watch is still active, then it is canceled, and the associated delegate is 71 // not notified. 72 // 73 // Returns true if the watch was canceled. Otherwise, false is returned. 74 // 75 bool StopWatching(); 76 77 // Returns the handle of the object being watched, or NULL if the object 78 // watcher is stopped. 79 HANDLE GetWatchedObject(); 80 81 private: 82 // Called on a background thread when done waiting. 83 static void CALLBACK DoneWaiting(void* param, BOOLEAN timed_out); 84 85 void Signal(Delegate* delegate); 86 87 // MessageLoop::DestructionObserver implementation: 88 virtual void WillDestroyCurrentMessageLoop(); 89 90 // Internal state. 91 Closure callback_; 92 HANDLE object_; // The object being watched 93 HANDLE wait_object_; // Returned by RegisterWaitForSingleObject 94 MessageLoop* origin_loop_; // Used to get back to the origin thread 95 96 WeakPtrFactory<ObjectWatcher> weak_factory_; 97 98 DISALLOW_COPY_AND_ASSIGN(ObjectWatcher); 99 }; 100 101 } // namespace win 102 } // namespace base 103 104 #endif // BASE_OBJECT_WATCHER_H_ 105
