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1 // Copyright (c) 2012 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_TASK_SEQUENCED_TASK_RUNNER_HELPERS_H_ | |
6 #define BASE_TASK_SEQUENCED_TASK_RUNNER_HELPERS_H_ | |
7 | |
8 #include "base/basictypes.h" | |
9 | |
10 // TODO(akalin): Investigate whether it's possible to just have | |
11 // SequencedTaskRunner use these helpers (instead of MessageLoop). | |
12 // Then we can just move these to sequenced_task_runner.h. | |
13 | |
14 namespace tracked_objects { | |
15 class Location; | |
16 } | |
17 | |
18 namespace base { | |
19 | |
20 namespace subtle { | |
21 template <class T, class R> class DeleteHelperInternal; | |
22 template <class T, class R> class ReleaseHelperInternal; | |
23 } | |
24 | |
25 // Template helpers which use function indirection to erase T from the | |
26 // function signature while still remembering it so we can call the | |
27 // correct destructor/release function. | |
28 // | |
29 // We use this trick so we don't need to include bind.h in a header | |
30 // file like sequenced_task_runner.h. We also wrap the helpers in a | |
31 // templated class to make it easier for users of DeleteSoon to | |
32 // declare the helper as a friend. | |
33 template <class T> | |
34 class DeleteHelper { | |
35 private: | |
36 template <class T2, class R> friend class subtle::DeleteHelperInternal; | |
37 | |
38 static void DoDelete(const void* object) { | |
39 delete reinterpret_cast<const T*>(object); | |
40 } | |
41 | |
42 DISALLOW_COPY_AND_ASSIGN(DeleteHelper); | |
43 }; | |
44 | |
45 template <class T> | |
46 class ReleaseHelper { | |
47 private: | |
48 template <class T2, class R> friend class subtle::ReleaseHelperInternal; | |
49 | |
50 static void DoRelease(const void* object) { | |
51 reinterpret_cast<const T*>(object)->Release(); | |
52 } | |
53 | |
54 DISALLOW_COPY_AND_ASSIGN(ReleaseHelper); | |
55 }; | |
56 | |
57 namespace subtle { | |
58 | |
59 // An internal SequencedTaskRunner-like class helper for DeleteHelper | |
60 // and ReleaseHelper. We don't want to expose the Do*() functions | |
61 // directly directly since the void* argument makes it possible to | |
62 // pass/ an object of the wrong type to delete. Instead, we force | |
63 // callers to go through these internal helpers for type | |
64 // safety. SequencedTaskRunner-like classes which expose DeleteSoon or | |
65 // ReleaseSoon methods should friend the appropriate helper and | |
66 // implement a corresponding *Internal method with the following | |
67 // signature: | |
68 // | |
69 // bool(const tracked_objects::Location&, | |
70 // void(*function)(const void*), | |
71 // void* object) | |
72 // | |
73 // An implementation of this function should simply create a | |
74 // base::Closure from (function, object) and return the result of | |
75 // posting the task. | |
76 template <class T, class ReturnType> | |
77 class DeleteHelperInternal { | |
78 public: | |
79 template <class SequencedTaskRunnerType> | |
80 static ReturnType DeleteViaSequencedTaskRunner( | |
81 SequencedTaskRunnerType* sequenced_task_runner, | |
82 const tracked_objects::Location& from_here, | |
83 const T* object) { | |
84 return sequenced_task_runner->DeleteSoonInternal( | |
85 from_here, &DeleteHelper<T>::DoDelete, object); | |
86 } | |
87 | |
88 private: | |
89 DISALLOW_COPY_AND_ASSIGN(DeleteHelperInternal); | |
90 }; | |
91 | |
92 template <class T, class ReturnType> | |
93 class ReleaseHelperInternal { | |
94 public: | |
95 template <class SequencedTaskRunnerType> | |
96 static ReturnType ReleaseViaSequencedTaskRunner( | |
97 SequencedTaskRunnerType* sequenced_task_runner, | |
98 const tracked_objects::Location& from_here, | |
99 const T* object) { | |
100 return sequenced_task_runner->ReleaseSoonInternal( | |
101 from_here, &ReleaseHelper<T>::DoRelease, object); | |
102 } | |
103 | |
104 private: | |
105 DISALLOW_COPY_AND_ASSIGN(ReleaseHelperInternal); | |
106 }; | |
107 | |
108 } // namespace subtle | |
109 | |
110 } // namespace base | |
111 | |
112 #endif // BASE_TASK_SEQUENCED_TASK_RUNNER_HELPERS_H_ | |
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