89590681f8
This is needed to allow the callback system to perform implicit conversions from the task result to the argument's call. Otherwise, the template resolution will force exact equality between the return type of the task and the reply's argument type which is too strict. For example, you wouldn't be able to take a const int & when returning an int. Also remove some DCHECKs that can't happen. BUG=159114 Review URL: https://chromiumcodereview.appspot.com/11369061 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169825 0039d316-1c4b-4281-b951-d872f2087c98
72 lines
2.3 KiB
C++
72 lines
2.3 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_TASK_RUNNER_UTIL_H_
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#define BASE_TASK_RUNNER_UTIL_H_
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#include "base/bind.h"
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#include "base/bind_helpers.h"
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#include "base/callback_internal.h"
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#include "base/logging.h"
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#include "base/task_runner.h"
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namespace base {
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namespace internal {
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// Adapts a function that produces a result via a return value to
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// one that returns via an output parameter.
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template <typename ReturnType>
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void ReturnAsParamAdapter(const Callback<ReturnType(void)>& func,
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ReturnType* result) {
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*result = func.Run();
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}
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// Adapts a T* result to a callblack that expects a T.
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template <typename TaskReturnType, typename ReplyArgType>
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void ReplyAdapter(const Callback<void(ReplyArgType)>& callback,
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TaskReturnType* result) {
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// TODO(ajwong): Remove this conditional and add a DCHECK to enforce that
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// |reply| must be non-null in PostTaskAndReplyWithResult() below after
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// current code that relies on this API softness has been removed.
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// http://crbug.com/162712
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if (!callback.is_null())
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callback.Run(CallbackForward(*result));
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}
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} // namespace internal
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// When you have these methods
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//
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// R DoWorkAndReturn();
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// void Callback(const R& result);
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//
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// and want to call them in a PostTaskAndReply kind of fashion where the
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// result of DoWorkAndReturn is passed to the Callback, you can use
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// PostTaskAndReplyWithResult as in this example:
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//
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// PostTaskAndReplyWithResult(
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// target_thread_.message_loop_proxy(),
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// FROM_HERE,
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// Bind(&DoWorkAndReturn),
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// Bind(&Callback));
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template <typename TaskReturnType, typename ReplyArgType>
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bool PostTaskAndReplyWithResult(
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TaskRunner* task_runner,
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const tracked_objects::Location& from_here,
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const Callback<TaskReturnType(void)>& task,
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const Callback<void(ReplyArgType)>& reply) {
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TaskReturnType* result = new TaskReturnType();
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return task_runner->PostTaskAndReply(
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from_here,
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base::Bind(&internal::ReturnAsParamAdapter<TaskReturnType>, task,
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result),
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base::Bind(&internal::ReplyAdapter<TaskReturnType, ReplyArgType>, reply,
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base::Owned(result)));
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}
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} // namespace base
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#endif // BASE_TASK_RUNNER_UTIL_H_
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