base/task_runner_util.h

   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 // Helper class for TaskRunner::PostTaskAndReplyWithResult.
  19 template <typename ReturnType>
  20 void ReturnAsParamAdapter(const Callback<ReturnType(void)>& func,
  21                           ReturnType* result) {
  22   if (!func.is_null())
  23     *result = func.Run();
  24 }
  25
  26 // Helper class for TaskRunner::PostTaskAndReplyWithResult.
  27 template <typename ReturnType>
  28 Closure ReturnAsParam(const Callback<ReturnType(void)>& func,
  29                       ReturnType* result) {
  30   DCHECK(result);
  31   return Bind(&ReturnAsParamAdapter<ReturnType>, func, result);
  32 }
  33
  34 // Helper class for TaskRunner::PostTaskAndReplyWithResult.
  35 template <typename ReturnType>
  36 void ReplyAdapter(const Callback<void(ReturnType)>& callback,
  37                   ReturnType* result) {
  38   DCHECK(result);
  39   if(!callback.is_null())
  40     callback.Run(CallbackForward(*result));
  41 }
  42
  43 // Helper class for TaskRunner::PostTaskAndReplyWithResult.
  44 template <typename ReturnType, typename OwnedType>
  45 Closure ReplyHelper(const Callback<void(ReturnType)>& callback,
  46                     OwnedType result) {
  47   return Bind(&ReplyAdapter<ReturnType>, callback, result);
  48 }
  49
  50 }  // namespace internal
  51
  52 // When you have these methods
  53 //
  54 //   R DoWorkAndReturn();
  55 //   void Callback(const R& result);
  56 //
  57 // and want to call them in a PostTaskAndReply kind of fashion where the
  58 // result of DoWorkAndReturn is passed to the Callback, you can use
  59 // PostTaskAndReplyWithResult as in this example:
  60 //
  61 // PostTaskAndReplyWithResult(
  62 //     target_thread_.message_loop_proxy(),
  63 //     FROM_HERE,
  64 //     Bind(&DoWorkAndReturn),
  65 //     Bind(&Callback));
  66 template <typename ReturnType>
  67 bool PostTaskAndReplyWithResult(
  68     TaskRunner* task_runner,
  69     const tracked_objects::Location& from_here,
  70     const Callback<ReturnType(void)>& task,
  71     const Callback<void(ReturnType)>& reply) {
  72   ReturnType* result = new ReturnType;
  73   return task_runner->PostTaskAndReply(
  74       from_here,
  75       internal::ReturnAsParam<ReturnType>(task, result),
  76       internal::ReplyHelper(reply, Owned(result)));
  77 }
  78
  79 }  // namespace base
  80
  81 #endif  // BASE_TASK_RUNNER_UTIL_H_