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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_SEQUENCED_TASK_RUNNER_HELPERS_H_ |
| 6 #define BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_ |
| 7 #pragma once |
| 8 |
| 9 #include "base/basictypes.h" |
| 10 |
| 11 // TODO(akalin): Investigate whether it's possible to just have |
| 12 // SequencedTaskRunner use these helpers (instead of MessageLoop). |
| 13 // Then we can just move these to sequenced_task_runner.h. |
| 14 |
| 15 namespace tracked_objects { |
| 16 class Location; |
| 17 } |
| 18 |
| 19 namespace base { |
| 20 |
| 21 namespace subtle { |
| 22 template <class T, class R> class DeleteHelperInternal; |
| 23 template <class T, class R> class ReleaseHelperInternal; |
| 24 } |
| 25 |
| 26 // Template helpers which use function indirection to erase T from the |
| 27 // function signature while still remembering it so we can call the |
| 28 // correct destructor/release function. |
| 29 // |
| 30 // We use this trick so we don't need to include bind.h in a header |
| 31 // file like sequenced_task_runner.h. We also wrap the helpers in a |
| 32 // templated class to make it easier for users of DeleteSoon to |
| 33 // declare the helper as a friend. |
| 34 template <class T> |
| 35 class DeleteHelper { |
| 36 private: |
| 37 template <class T2, class R> friend class subtle::DeleteHelperInternal; |
| 38 |
| 39 static void DoDelete(const void* object) { |
| 40 delete reinterpret_cast<const T*>(object); |
| 41 } |
| 42 |
| 43 DISALLOW_COPY_AND_ASSIGN(DeleteHelper); |
| 44 }; |
| 45 |
| 46 template <class T> |
| 47 class ReleaseHelper { |
| 48 private: |
| 49 template <class T2, class R> friend class subtle::ReleaseHelperInternal; |
| 50 |
| 51 static void DoRelease(const void* object) { |
| 52 reinterpret_cast<const T*>(object)->Release(); |
| 53 } |
| 54 |
| 55 DISALLOW_COPY_AND_ASSIGN(ReleaseHelper); |
| 56 }; |
| 57 |
| 58 namespace subtle { |
| 59 |
| 60 // An internal SequencedTaskRunner-like class helper for DeleteHelper |
| 61 // and ReleaseHelper. We don't want to expose the Do*() functions |
| 62 // directly directly since the void* argument makes it possible to |
| 63 // pass/ an object of the wrong type to delete. Instead, we force |
| 64 // callers to go through these internal helpers for type |
| 65 // safety. SequencedTaskRunner-like classes which expose DeleteSoon or |
| 66 // ReleaseSoon methods should friend the appropriate helper and |
| 67 // implement a corresponding *Internal method with the following |
| 68 // signature: |
| 69 // |
| 70 // bool(const tracked_objects::Location&, |
| 71 // void(*function)(const void*), |
| 72 // void* object) |
| 73 // |
| 74 // An implementation of this function should simply create a |
| 75 // base::Closure from (function, object) and return the result of |
| 76 // posting the task. |
| 77 template <class T, class ReturnType> |
| 78 class DeleteHelperInternal { |
| 79 public: |
| 80 template <class SequencedTaskRunnerType> |
| 81 static ReturnType DeleteViaSequencedTaskRunner( |
| 82 SequencedTaskRunnerType* sequenced_task_runner, |
| 83 const tracked_objects::Location& from_here, |
| 84 const T* object) { |
| 85 return sequenced_task_runner->DeleteSoonInternal( |
| 86 from_here, &DeleteHelper<T>::DoDelete, object); |
| 87 } |
| 88 |
| 89 private: |
| 90 DISALLOW_COPY_AND_ASSIGN(DeleteHelperInternal); |
| 91 }; |
| 92 |
| 93 template <class T, class ReturnType> |
| 94 class ReleaseHelperInternal { |
| 95 public: |
| 96 template <class SequencedTaskRunnerType> |
| 97 static ReturnType ReleaseViaSequencedTaskRunner( |
| 98 SequencedTaskRunnerType* sequenced_task_runner, |
| 99 const tracked_objects::Location& from_here, |
| 100 const T* object) { |
| 101 return sequenced_task_runner->ReleaseSoonInternal( |
| 102 from_here, &ReleaseHelper<T>::DoRelease, object); |
| 103 } |
| 104 |
| 105 private: |
| 106 DISALLOW_COPY_AND_ASSIGN(ReleaseHelperInternal); |
| 107 }; |
| 108 |
| 109 } // namespace subtle |
| 110 |
| 111 } // namespace base |
| 112 |
| 113 #endif // BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_ |
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