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#include "base/debug/alias.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
15namespace tracked_objects {
16class Location;
17}
18
19namespace base {
20
21namespace subtle {
22template <class T, class R> class DeleteHelperInternal;
23template <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.
34template <class T>
35class 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
46template <class T>
47class 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
58namespace 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.
77template <class T, class ReturnType>
78class 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
93template <class T, class ReturnType>
94class 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