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_TASK_RUNNER_UTIL_H_
6#define BASE_TASK_RUNNER_UTIL_H_
7
8#include "base/bind.h"
9#include "base/bind_helpers.h"
10#include "base/callback_internal.h"
11#include "base/logging.h"
12#include "base/task_runner.h"
13
14namespace base {
15
16namespace internal {
17
18// Adapts a function that produces a result via a return value to
19// one that returns via an output parameter.
20template <typename ReturnType>
21void ReturnAsParamAdapter(const Callback<ReturnType(void)>& func,
22                          ReturnType* result) {
23  *result = func.Run();
24}
25
26// Adapts a T* result to a callblack that expects a T.
27template <typename TaskReturnType, typename ReplyArgType>
28void ReplyAdapter(const Callback<void(ReplyArgType)>& callback,
29                  TaskReturnType* result) {
30  // TODO(ajwong): Remove this conditional and add a DCHECK to enforce that
31  // |reply| must be non-null in PostTaskAndReplyWithResult() below after
32  // current code that relies on this API softness has been removed.
33  // http://crbug.com/162712
34  if (!callback.is_null())
35    callback.Run(CallbackForward(*result));
36}
37
38}  // namespace internal
39
40// When you have these methods
41//
42//   R DoWorkAndReturn();
43//   void Callback(const R& result);
44//
45// and want to call them in a PostTaskAndReply kind of fashion where the
46// result of DoWorkAndReturn is passed to the Callback, you can use
47// PostTaskAndReplyWithResult as in this example:
48//
49// PostTaskAndReplyWithResult(
50//     target_thread_.task_runner(),
51//     FROM_HERE,
52//     Bind(&DoWorkAndReturn),
53//     Bind(&Callback));
54template <typename TaskReturnType, typename ReplyArgType>
55bool PostTaskAndReplyWithResult(
56    TaskRunner* task_runner,
57    const tracked_objects::Location& from_here,
58    const Callback<TaskReturnType(void)>& task,
59    const Callback<void(ReplyArgType)>& reply) {
60  TaskReturnType* result = new TaskReturnType();
61  return task_runner->PostTaskAndReply(
62      from_here,
63      base::Bind(&internal::ReturnAsParamAdapter<TaskReturnType>, task,
64                 result),
65      base::Bind(&internal::ReplyAdapter<TaskReturnType, ReplyArgType>, reply,
66                 base::Owned(result)));
67}
68
69}  // namespace base
70
71#endif  // BASE_TASK_RUNNER_UTIL_H_
72