1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
|
// 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_
|
