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
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kReplication
#include "mongo/db/repl/topology_version_observer.h"
#include "mongo/base/status_with.h"
#include "mongo/db/client.h"
#include "mongo/db/operation_context.h"
#include "mongo/logv2/log.h"
#include "mongo/util/assert_util.h"
namespace mongo {
namespace repl {
void TopologyVersionObserver::init(ReplicationCoordinator* replCoordinator) noexcept {
invariant(replCoordinator);
stdx::lock_guard<Mutex> lk(_mutex);
invariant(_state.load() == State::kUninitialized);
LOGV2_INFO(40440,
"Starting {topologyVersionObserverName}",
"topologyVersionObserverName"_attr = toString());
_replCoordinator = replCoordinator;
invariant(!_thread);
_thread = stdx::thread([&]() { this->_workerThreadBody(); });
// Wait for the observer thread to update the status.
while (_state.load() != State::kRunning) {
}
}
void TopologyVersionObserver::shutdown() noexcept {
stdx::unique_lock<Mutex> lk(_mutex);
if (_state.load() == State::kUninitialized) {
return;
}
// Check if another `shutdown()` has already completed.
if (!_thread) {
return;
}
LOGV2_INFO(40441,
"Stopping {topologyVersionObserverName}",
"topologyVersionObserverName"_attr = toString());
auto state = _state.load();
invariant(state == State::kRunning || state == State::kShutdown);
// Wait for the observer client to exit from its main loop.
// Observer thread must update the state before attempting to acquire the mutex.
while (_state.load() == State::kRunning) {
invariant(_observerClient);
_observerClient->lock();
auto opCtx = _observerClient->getOperationContext();
if (opCtx) {
opCtx->markKilled(ErrorCodes::ShutdownInProgress);
}
_observerClient->unlock();
}
invariant(_state.load() == State::kShutdown);
auto thread = std::exchange(_thread, boost::none);
lk.unlock();
invariant(thread);
thread->join();
}
std::shared_ptr<const IsMasterResponse> TopologyVersionObserver::getCached() noexcept {
// Acquires the lock to avoid potential races with `_workerThreadBody()`.
// Atomics cannot be used here as `shared_ptr` cannot be atomically updated.
stdx::lock_guard<Mutex> lk(_mutex);
return _cache;
}
std::string TopologyVersionObserver::toString() const {
return str::stream() << kTopologyVersionObserverName;
}
std::shared_ptr<const IsMasterResponse> TopologyVersionObserver::_getIsMasterResponse(
boost::optional<TopologyVersion> topologyVersion, bool* shouldShutdown) try {
invariant(*shouldShutdown == false);
ServiceContext::UniqueOperationContext opCtx;
try {
opCtx = Client::getCurrent()->makeOperationContext();
} catch (...) {
// Failure to create an operation context could cause deadlocks.
*shouldShutdown = true;
LOGV2_WARNING(40442, "Observer was unable to create a new OperationContext.");
return nullptr;
}
invariant(opCtx);
auto future = _replCoordinator->getIsMasterResponseFuture({}, topologyVersion);
auto response = future.get(opCtx.get());
if (!response->isConfigSet()) {
return nullptr;
}
return response;
} catch (const ExceptionForCat<ErrorCategory::ShutdownError>& e) {
LOGV2_WARNING(
40443, "Observer was interrupted by {exception}", "exception"_attr = e.toString());
*shouldShutdown = true;
return nullptr;
} catch (DBException& e) {
LOGV2_WARNING(40444,
"Observer could not retrieve isMasterResponse: {exception}",
"exception"_attr = e.toString());
return nullptr;
}
void TopologyVersionObserver::_workerThreadBody() noexcept {
invariant(_state.load() == State::kUninitialized);
// Creates a new client and makes `_observerClient` to point to it, which allows `shutdown()`
// to access the client object.
Client::initThread(kTopologyVersionObserverName);
_observerClient = Client::getCurrent();
// `init()` must hold the mutex until the observer updates the state.
invariant(!_mutex.try_lock());
// The following notifies `init()` that `_observerClient` is set and ready to use.
_state.store(State::kRunning);
auto getTopologyVersion = [&]() -> boost::optional<TopologyVersion> {
// Only the observer thread updates `_cache`, thus there is no need to hold the lock before
// accessing `_cache` here.
if (_cache) {
return _cache->getTopologyVersion();
}
return boost::none;
};
ON_BLOCK_EXIT([&] {
// Once the observer detects a shutdown, it must update the state first before attempting
// to acquire the lock. This is necessary to avoid deadlocks.
invariant(_state.load() == State::kRunning);
_state.store(State::kShutdown);
stdx::unique_lock lock(_mutex);
// Invalidate the cache as it is no longer updated
_cache.reset();
// Client object is local to this thread, and is no longer be available.
_observerClient = nullptr;
LOGV2_INFO(40447,
"Stopped {topologyVersionObserverName}",
"topologyVersionObserverName"_attr = toString());
});
bool shouldShutdown = false;
LOGV2_INFO(40445,
"Started {topologyVersionObserverName}",
"topologyVersionObserverName"_attr = toString());
while (!shouldShutdown) {
auto response = _getIsMasterResponse(getTopologyVersion(), &shouldShutdown);
// Only update if the version is more recent than the cached version, or `_cache` is null.
if (!shouldShutdown && response != _cache) {
stdx::lock_guard lock(_mutex);
_cache = response;
}
}
}
} // namespace repl
} // namespace mongo
|
