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
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
|
/**
* Copyright (C) 2016 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#include <boost/optional.hpp>
#include "mongo/db/operation_context.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/duration.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* Allows waiting for a result returned from an asynchronous operation.
*/
template <class T>
class Notification {
public:
Notification() = default;
/**
* Creates a notification object, which has already been set. Calls to any of the getters will
* return immediately.
*/
explicit Notification(T value) : _value(value) {}
/**
* Returns true if the notification has been set (i.e., the call to get/waitFor would not
* block).
*/
explicit operator bool() const {
stdx::unique_lock<stdx::mutex> lock(_mutex);
return !!_value;
}
/**
* If the notification has been set, returns immediately. Otherwise blocks until it becomes set.
* If the wait is interrupted, throws an exception.
*/
T& get(OperationContext* opCtx) {
stdx::unique_lock<stdx::mutex> lock(_mutex);
opCtx->waitForConditionOrInterrupt(_condVar, lock, [this]() -> bool { return !!_value; });
return _value.get();
}
/**
* If the notification has been set, returns immediately. Otherwise blocks until it becomes set.
* This variant of get cannot be interrupted.
*/
T& get() {
stdx::unique_lock<stdx::mutex> lock(_mutex);
while (!_value) {
_condVar.wait(lock);
}
return _value.get();
}
/**
* Sets the notification result and wakes up any threads, which might be blocked in the wait
* call. Must only be called once for the lifetime of the notification.
*/
void set(T value) {
stdx::lock_guard<stdx::mutex> lock(_mutex);
invariant(!_value);
_value = std::move(value);
_condVar.notify_all();
}
/**
* If the notification is set, returns immediately. Otherwise, blocks until it either becomes
* set or the waitTimeout expires, whichever comes first. Returns true if the notification is
* set (in which case a subsequent call to get is guaranteed to not block) or false otherwise.
* If the wait is interrupted, throws an exception.
*/
bool waitFor(OperationContext* opCtx, Milliseconds waitTimeout) {
stdx::unique_lock<stdx::mutex> lock(_mutex);
return opCtx->waitForConditionOrInterruptFor(
_condVar, lock, waitTimeout, [&]() { return !!_value; });
}
private:
mutable stdx::mutex _mutex;
stdx::condition_variable _condVar;
// Protected by mutex and only moves from not-set to set once
boost::optional<T> _value{boost::none};
};
template <>
class Notification<void> {
public:
explicit operator bool() const {
return _notification.operator bool();
}
void get(OperationContext* opCtx) {
_notification.get(opCtx);
}
void get() {
_notification.get();
}
void set() {
_notification.set(true);
}
bool waitFor(OperationContext* opCtx, Milliseconds waitTimeout) {
return _notification.waitFor(opCtx, waitTimeout);
}
private:
Notification<bool> _notification;
};
} // namespace mongo
|