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1 // Copyright 2013 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 SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_SIGNAL_H_ | |
6 #define SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_SIGNAL_H_ | |
7 | |
8 #include "base/synchronization/lock.h" | |
9 #include "sync/base/sync_export.h" | |
10 | |
11 namespace syncer { | |
12 | |
13 class CancelationObserver; | |
14 | |
15 // This class is used to allow one thread to request that another abort and | |
16 // return early. | |
17 // | |
18 // The signalling thread owns this class and my call Signal() at any time. | |
19 // After that call, this class' IsSignalled() will always return true. The | |
20 // intended use case is that the task intending to support early exit will | |
21 // periodically check the value of IsSignalled() to see if it should return | |
22 // early. | |
23 // | |
24 // The receiving task may also choose to register an CancelationObserver whose | |
25 // OnSignalReceived() method will be executed on the signaller's thread when | |
26 // Signal() is called. This may be used for sending an early Signal() to a | |
27 // WaitableEvent. The registration of the handler is necessarily racy. If | |
28 // Signal() is executes before TryRegisterHandler(), TryRegisterHandler() will | |
29 // not perform any registration and return false. That function's caller must | |
30 // handle this case. | |
31 // | |
32 // This class supports only one handler, though it could easily support multiple | |
33 // observers if we found a use case for such a feature. | |
34 class SYNC_EXPORT CancelationSignal { | |
35 public: | |
36 CancelationSignal(); | |
37 ~CancelationSignal(); | |
38 | |
39 // Tries to register a handler to be invoked when Signal() is called. | |
40 // | |
41 // If Signal() has already been called, returns false without registering | |
42 // the handler. Returns true when the registration is successful. | |
43 // | |
44 // If the registration was successful, the handler must be unregistered with | |
45 // UnregisterHandler before this CancelationSignal is destroyed. | |
46 bool TryRegisterHandler(CancelationObserver* handler); | |
47 | |
48 // Unregisters the abort handler. | |
49 void UnregisterHandler(CancelationObserver* handler); | |
50 | |
51 // Returns true if Signal() has been called. | |
52 bool IsSignalled(); | |
53 | |
54 // Sets the stop_requested_ flag and calls the OnSignalReceived() method of | |
55 // the registered handler, if there is one registered at the time. | |
56 // SignalReceived() will be called with the |signal_lock_| held. | |
57 void Signal(); | |
58 | |
59 private: | |
60 // Protects all members of this class. | |
61 base::Lock signal_lock_; | |
62 | |
63 // True if Signal() has been invoked. | |
64 bool signalled_; | |
65 | |
66 // The registered abort handler. May be NULL. | |
67 CancelationObserver* handler_; | |
68 }; | |
69 | |
70 } // namespace syncer | |
71 | |
72 #endif // SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_SIGNAL_H_ | |
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