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