post_task_and_reply_impl.cc | Explore in Territory

// 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.

#include "base/threading/post_task_and_reply_impl.h"

#include <utility>

#include "base/check_op.h"
#include "base/debug/leak_annotations.h"
#include "base/task/sequenced_task_runner.h"
#include "base/task/thread_pool/thread_pool_instance.h"

namespace base::internal {

PostTaskAndReplyRelay::PostTaskAndReplyRelay(
    const Location& from_here,
    OnceClosure task,
    OnceClosure reply,
    scoped_refptr<SequencedTaskRunner> reply_task_runner)
    : … { … }

PostTaskAndReplyRelay::PostTaskAndReplyRelay(PostTaskAndReplyRelay&&) = default;

// It is important that `reply_` always be deleted on the origin sequence
// (`reply_task_runner_`) since its destructor can be affine to it. More
// sutbly, it is also important that `task_` be destroyed on the origin
// sequence when it fails to run. This is because `task_` can own state which
// is affine to `reply_task_runner_` and was intended to be handed to
// `reply_`, e.g. https://crbug.com/829122. Since `task_` already needs to
// support deletion on the origin sequence (since the initial PostTask can
// always fail), it's safer to delete it there when PostTask succeeds but
// `task_` is later prevented from running.
//
// PostTaskAndReplyRelay's move semantics along with logic in this destructor
// enforce the above semantics in all the following cases :
//  1) Posting `task_` fails right away on the origin sequence:
//    a) `reply_task_runner_` is null (i.e. during late shutdown);
//    b) `reply_task_runner_` is set.
//  2) ~PostTaskAndReplyRelay() runs on the destination sequence:
//    a) RunTaskAndPostReply() is cancelled before running;
//    b) RunTaskAndPostReply() is skipped on shutdown;
//    c) Posting RunReply() fails.
//  3) ~PostTaskAndReplyRelay() runs on the origin sequence:
//    a) RunReply() is cancelled before running;
//    b) RunReply() is skipped on shutdown;
//    c) The DeleteSoon() posted by (2) runs.
//  4) ~PostTaskAndReplyRelay() should no-op:
//    a) This relay was moved to another relay instance;
//    b) RunReply() ran and completed this relay's mandate.
PostTaskAndReplyRelay::~PostTaskAndReplyRelay() { … }

}  // namespace base::internal
chromium/base/threading/post_task_and_reply_impl.cc
