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