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
|
/**
* Copyright (C) 2018-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.
*/
#pragma once
#include "mongo/base/disallow_copying.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/oid.h"
#include "mongo/stdx/chrono.h"
namespace mongo {
using DistLockHandle = OID;
class OperationContext;
class Status;
template <typename T>
class StatusWith;
/**
* Interface for handling distributed locks.
*
* Usage:
*
* auto scopedDistLock = mgr->lock(...);
*
* if (!scopedDistLock.isOK()) {
* // Did not get lock. scopedLockStatus destructor will not call unlock.
* }
*
* // To check if lock is still owned:
* auto status = scopedDistLock.getValue().checkStatus();
*
* if (!status.isOK()) {
* // Someone took over the lock! Unlock will still be called at destructor, but will
* // practically be a no-op since it doesn't own the lock anymore.
* }
*/
class DistLockManager {
public:
// Default timeout which will be used if one is not passed to the lock method.
static const Seconds kDefaultLockTimeout;
// Timeout value, which specifies that if the lock is not available immediately, no attempt
// should be made to wait for it to become free.
static const Milliseconds kSingleLockAttemptTimeout;
/**
* RAII type for distributed lock. Not meant to be shared across multiple threads.
*/
class ScopedDistLock {
MONGO_DISALLOW_COPYING(ScopedDistLock);
public:
ScopedDistLock(OperationContext* opCtx,
DistLockHandle lockHandle,
DistLockManager* lockManager);
~ScopedDistLock();
ScopedDistLock(ScopedDistLock&& other);
ScopedDistLock& operator=(ScopedDistLock&& other);
/**
* Checks whether the lock is still being held by querying the config server.
*/
Status checkStatus();
private:
OperationContext* _opCtx;
DistLockHandle _lockID;
DistLockManager* _lockManager; // Not owned here.
};
virtual ~DistLockManager() = default;
/**
* Performs bootstrapping for the manager. Implementation do not need to guarantee
* thread safety so callers should employ proper synchronization when calling this method.
*/
virtual void startUp() = 0;
/**
* Cleanup the manager's resources. Implementations do not need to guarantee thread safety
* so callers should employ proper synchronization when calling this method.
*/
virtual void shutDown(OperationContext* opCtx) = 0;
/**
* Returns the process ID for this DistLockManager.
*/
virtual std::string getProcessID() = 0;
/**
* Tries multiple times to lock, using the specified lock try interval, until
* a certain amount of time has passed or when any error that is not LockBusy
* occurred.
*
* waitFor = 0 indicates there should only be one attempt to acquire the lock, and
* no waiting.
* waitFor = -1 indicates we should retry indefinitely.
*
* Returns OK if the lock was successfully acquired.
* Returns ErrorCodes::DistributedClockSkewed when a clock skew is detected.
* Returns ErrorCodes::LockBusy if the lock is being held.
*/
StatusWith<ScopedDistLock> lock(OperationContext* opCtx,
StringData name,
StringData whyMessage,
Milliseconds waitFor);
/**
* Same behavior as lock(...) above, except takes a specific lock session ID "lockSessionID"
* instead of randomly generating one internally.
*
* This is useful for a process running on the config primary after a failover. A lock can be
* immediately reacquired if "lockSessionID" matches that of the lock, rather than waiting for
* the inactive lock to expire.
*/
virtual StatusWith<DistLockHandle> lockWithSessionID(OperationContext* opCtx,
StringData name,
StringData whyMessage,
const OID& lockSessionID,
Milliseconds waitFor) = 0;
/**
* Specialized locking method, which only succeeds if the specified lock name is not held by
* anyone. Uses local write concern and does not attempt to overtake the lock or check whether
* the lock lease has expired.
*/
virtual StatusWith<DistLockHandle> tryLockWithLocalWriteConcern(OperationContext* opCtx,
StringData name,
StringData whyMessage,
const OID& lockSessionID) = 0;
/**
* Unlocks the given lockHandle. Will attempt to retry again later if the config
* server is not reachable.
*/
virtual void unlock(OperationContext* opCtx, const DistLockHandle& lockHandle) = 0;
/**
* Unlocks the lock specified by "lockHandle" and "name". Will attempt to retry again later if
* the config server is not reachable.
*/
virtual void unlock(OperationContext* opCtx,
const DistLockHandle& lockHandle,
StringData name) = 0;
/**
* Makes a best-effort attempt to unlock all locks owned by the given processID.
*/
virtual void unlockAll(OperationContext* opCtx, const std::string& processID) = 0;
protected:
/**
* Checks if the lockHandle still exists in the config server.
*/
virtual Status checkStatus(OperationContext* opCtx, const DistLockHandle& lockHandle) = 0;
};
} // namespace mongo
|
