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 8 #include "base/debug/alias.h" 9 #include "base/macros.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_ 114
