| // Copyright 2011 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // This file defines a common helper encapsulating the tricky bits of |
| // implementing PostTaskAndReply(). These tricky bits are specifically around |
| // handling of the reply callback and ensuring it is deleted on the correct |
| // sequence. |
| |
| #ifndef BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_ |
| #define BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_ |
| |
| #include <utility> |
| |
| #include "base/base_export.h" |
| #include "base/check_op.h" |
| #include "base/functional/bind.h" |
| #include "base/functional/callback.h" |
| #include "base/location.h" |
| #include "base/memory/scoped_refptr.h" |
| #include "base/task/sequenced_task_runner.h" |
| |
| namespace base::internal { |
| |
| class BASE_EXPORT PostTaskAndReplyRelay { |
| public: |
| PostTaskAndReplyRelay(const Location& from_here, |
| OnceClosure task, |
| OnceClosure reply, |
| scoped_refptr<SequencedTaskRunner> reply_task_runner); |
| |
| PostTaskAndReplyRelay(PostTaskAndReplyRelay&&); |
| // No assignment operator because of const member. |
| PostTaskAndReplyRelay& operator=(PostTaskAndReplyRelay&&) = delete; |
| |
| PostTaskAndReplyRelay(const PostTaskAndReplyRelay&) = delete; |
| PostTaskAndReplyRelay& operator=(const PostTaskAndReplyRelay&) = delete; |
| |
| ~PostTaskAndReplyRelay(); |
| |
| // Static function is used because it is not possible to bind a method call to |
| // a non-pointer type. |
| static void RunTaskAndPostReply(PostTaskAndReplyRelay relay) { |
| DCHECK(relay.task_); |
| std::move(relay.task_).Run(); |
| |
| // Keep a pointer to the reply TaskRunner for the PostTask() call before |
| // |relay| is moved into a callback. |
| SequencedTaskRunner* reply_task_runner_raw = relay.reply_task_runner_.get(); |
| |
| const Location from_here = relay.from_here_; |
| reply_task_runner_raw->PostTask( |
| from_here, |
| BindOnce(&PostTaskAndReplyRelay::RunReply, std::move(relay))); |
| } |
| |
| private: |
| // Static function is used because it is not possible to bind a method call to |
| // a non-pointer type. |
| static void RunReply(PostTaskAndReplyRelay relay) { |
| DCHECK(!relay.task_); |
| DCHECK(relay.reply_); |
| std::move(relay.reply_).Run(); |
| } |
| |
| const Location from_here_; |
| OnceClosure task_; |
| OnceClosure reply_; |
| // Not const to allow moving. |
| scoped_refptr<SequencedTaskRunner> reply_task_runner_; |
| }; |
| |
| // Precondition: `SequencedTaskRunner::HasCurrentDefault()` must be true. |
| // |
| // Posts `task` by calling `task_poster`. On completion, posts `reply` to the |
| // origin sequence. Each callback is deleted synchronously after running, or |
| // scheduled for asynchronous deletion on the origin sequence if it can't run |
| // (e.g. if a TaskRunner skips it on shutdown). In this case, the callback may |
| // leak: see `SequencedTaskRunner::DeleteSoon()` for details about when objects |
| // scheduled for asynchronous deletion can be leaked. |
| // |
| // Note: All //base task posting APIs require callbacks to support deletion on |
| // the posting sequence if they can't be scheduled. |
| template <typename TaskPoster> |
| bool PostTaskAndReplyImpl(TaskPoster task_poster, |
| const Location& from_here, |
| OnceClosure task, |
| OnceClosure reply) { |
| DCHECK(task) << from_here.ToString(); |
| DCHECK(reply) << from_here.ToString(); |
| |
| const bool has_sequenced_context = SequencedTaskRunner::HasCurrentDefault(); |
| |
| const bool post_task_success = task_poster( |
| from_here, BindOnce(&PostTaskAndReplyRelay::RunTaskAndPostReply, |
| PostTaskAndReplyRelay( |
| from_here, std::move(task), std::move(reply), |
| has_sequenced_context |
| ? SequencedTaskRunner::GetCurrentDefault() |
| : nullptr))); |
| |
| // PostTaskAndReply() requires a SequencedTaskRunner::CurrentDefaultHandle to |
| // post the reply. Having no SequencedTaskRunner::CurrentDefaultHandle is |
| // allowed when posting the task fails, to simplify calls during shutdown |
| // (https://crbug.com/922938). |
| CHECK(has_sequenced_context || !post_task_success); |
| |
| return post_task_success; |
| } |
| |
| } // namespace base::internal |
| |
| #endif // BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_ |