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 // Adapts a function that produces a result via a return value to
  19 // one that returns via an output parameter.
  20 template <typename ReturnType>
  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>
  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_.message_loop_proxy(),
  51 //     FROM_HERE,
  52 //     Bind(&DoWorkAndReturn),
  53 //     Bind(&Callback));
  54 template <typename TaskReturnType, typename ReplyArgType>
  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_