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/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 DoDelete(const void * object)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 DoRelease(const void * object)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> DeleteViaSequencedTaskRunner(SequencedTaskRunnerType * sequenced_task_runner,const tracked_objects::Location & from_here,const T * object)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> ReleaseViaSequencedTaskRunner(SequencedTaskRunnerType * sequenced_task_runner,const tracked_objects::Location & from_here,const T * object)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_SEQUENCED_TASK_RUNNER_HELPERS_H_ 113