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
14 namespace base {
15
16 namespace internal {
17
18 // Adapts a function that produces a result via a return value to
19 // one that returns via an output parameter.
20 template <typename ReturnType>
ReturnAsParamAdapter(const Callback<ReturnType (void)> & func,ReturnType * result)21 void 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.
27 template <typename TaskReturnType, typename ReplyArgType>
ReplyAdapter(const Callback<void (ReplyArgType)> & callback,TaskReturnType * result)28 void 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));
54 template <typename TaskReturnType, typename ReplyArgType>
PostTaskAndReplyWithResult(TaskRunner * task_runner,const tracked_objects::Location & from_here,const Callback<TaskReturnType (void)> & task,const Callback<void (ReplyArgType)> & reply)55 bool 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