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 14namespace tracked_objects { 15class Location; 16} 17 18namespace base { 19 20namespace subtle { 21template <class T, class R> class DeleteHelperInternal; 22template <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. 33template <class T> 34class 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 45template <class T> 46class 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 57namespace 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. 76template <class T, class ReturnType> 77class 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 92template <class T, class ReturnType> 93class 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_SEQUENCED_TASK_RUNNER_HELPERS_H_ 113