1 : // Copyright (c) 2006-2008 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_WAITABLE_EVENT_WATCHER_H_
6 : #define BASE_WAITABLE_EVENT_WATCHER_H_
7 :
8 : #include "build/build_config.h"
9 :
10 : #if defined(OS_WIN)
11 : #include "base/object_watcher.h"
12 : #else
13 : #include "base/message_loop.h"
14 : #include "base/waitable_event.h"
15 : #endif
16 :
17 : namespace base {
18 :
19 : class Flag;
20 : class AsyncWaiter;
21 : class AsyncCallbackTask;
22 : class WaitableEvent;
23 :
24 : // -----------------------------------------------------------------------------
25 : // This class provides a way to wait on a WaitableEvent asynchronously.
26 : //
27 : // Each instance of this object can be waiting on a single WaitableEvent. When
28 : // the waitable event is signaled, a callback is made in the thread of a given
29 : // MessageLoop. This callback can be deleted by deleting the waiter.
30 : //
31 : // Typical usage:
32 : //
33 : // class MyClass : public base::WaitableEventWatcher::Delegate {
34 : // public:
35 : // void DoStuffWhenSignaled(WaitableEvent *waitable_event) {
36 : // watcher_.StartWatching(waitable_event, this);
37 : // }
38 : // virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) {
39 : // // OK, time to do stuff!
40 : // }
41 : // private:
42 : // base::WaitableEventWatcher watcher_;
43 : // };
44 : //
45 : // In the above example, MyClass wants to "do stuff" when waitable_event
46 : // becomes signaled. WaitableEventWatcher makes this task easy. When MyClass
47 : // goes out of scope, the watcher_ will be destroyed, and there is no need to
48 : // worry about OnWaitableEventSignaled being called on a deleted MyClass
49 : // pointer.
50 : //
51 : // BEWARE: With automatically reset WaitableEvents, a signal may be lost if it
52 : // occurs just before a WaitableEventWatcher is deleted. There is currently no
53 : // safe way to stop watching an automatic reset WaitableEvent without possibly
54 : // missing a signal.
55 : //
56 : // NOTE: you /are/ allowed to delete the WaitableEvent while still waiting on
57 : // it with a Watcher. It will act as if the event was never signaled.
58 : // -----------------------------------------------------------------------------
59 :
60 : class WaitableEventWatcher
61 : #if defined(OS_POSIX)
62 : : public MessageLoop::DestructionObserver
63 : #endif
64 : {
65 : public:
66 :
67 : WaitableEventWatcher();
68 : ~WaitableEventWatcher();
69 :
70 1 : class Delegate {
71 : public:
72 0 : virtual ~Delegate() { }
73 :
74 : // -------------------------------------------------------------------------
75 : // This is called on the MessageLoop thread when WaitableEvent has been
76 : // signaled.
77 : //
78 : // Note: the event may not be signaled by the time that this function is
79 : // called. This indicates only that it has been signaled at some point in
80 : // the past.
81 : // -------------------------------------------------------------------------
82 : virtual void OnWaitableEventSignaled(WaitableEvent* waitable_event) = 0;
83 : };
84 :
85 : // ---------------------------------------------------------------------------
86 : // When @event is signaled, the given delegate is called on the thread of the
87 : // current message loop when StartWatching is called. The delegate is not
88 : // deleted.
89 : // ---------------------------------------------------------------------------
90 : bool StartWatching(WaitableEvent* event, Delegate* delegate);
91 :
92 : // ---------------------------------------------------------------------------
93 : // Cancel the current watch. Must be called from the same thread which
94 : // started the watch.
95 : //
96 : // Does nothing if no event is being watched, nor if the watch has completed.
97 : // The delegate will *not* be called for the current watch after this
98 : // function returns. Since the delegate runs on the same thread as this
99 : // function, it cannot be called during this function either.
100 : // ---------------------------------------------------------------------------
101 : void StopWatching();
102 :
103 : // ---------------------------------------------------------------------------
104 : // Return the currently watched event, or NULL if no object is currently being
105 : // watched.
106 : // ---------------------------------------------------------------------------
107 : WaitableEvent* GetWatchedEvent();
108 :
109 : private:
110 : WaitableEvent* event_;
111 :
112 : #if defined(OS_WIN)
113 : // ---------------------------------------------------------------------------
114 : // The helper class exists because, if WaitableEventWatcher were to inherit
115 : // from ObjectWatcher::Delegate, then it couldn't also have an inner class
116 : // called Delegate (at least on Windows). Thus this object exists to proxy
117 : // the callback function
118 : // ---------------------------------------------------------------------------
119 : class ObjectWatcherHelper : public ObjectWatcher::Delegate {
120 : public:
121 : ObjectWatcherHelper(WaitableEventWatcher* watcher);
122 :
123 : // -------------------------------------------------------------------------
124 : // Implementation of ObjectWatcher::Delegate
125 : // -------------------------------------------------------------------------
126 : void OnObjectSignaled(HANDLE h);
127 :
128 : private:
129 : WaitableEventWatcher *const watcher_;
130 : };
131 :
132 : void OnObjectSignaled();
133 :
134 : Delegate* delegate_;
135 : ObjectWatcherHelper helper_;
136 : ObjectWatcher watcher_;
137 : #else
138 : // ---------------------------------------------------------------------------
139 : // Implementation of MessageLoop::DestructionObserver
140 : // ---------------------------------------------------------------------------
141 : void WillDestroyCurrentMessageLoop();
142 :
143 : MessageLoop* message_loop_;
144 : scoped_refptr<Flag> cancel_flag_;
145 : AsyncWaiter* waiter_;
146 : AsyncCallbackTask* callback_task_;
147 : scoped_refptr<WaitableEvent::WaitableEventKernel> kernel_;
148 : #endif
149 : };
150 :
151 : } // namespace base
152 :
153 : #endif // BASE_WAITABLE_EVENT_WATCHER_H_
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