Repository navigation
Expand file tree
/
Copy pathlrwmutex.go
More file actions
189 lines (160 loc) · 4.61 KB
/
Copy pathlrwmutex.go
File metadata and controls
189 lines (160 loc) · 4.61 KB
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
/*
* Minio Cloud Storage, (C) 2017 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package lsync
import (
"context"
"math"
"math/rand"
"sync"
"time"
)
// A LRWMutex is a mutual exclusion lock with timeouts.
type LRWMutex struct {
id string
source string
isWriteLock bool
ref int
m sync.Mutex // Mutex to prevent multiple simultaneous locks
}
// NewLRWMutex - initializes a new lsync RW mutex.
func NewLRWMutex() *LRWMutex {
return &LRWMutex{}
}
// Lock holds a write lock on lm.
//
// If the lock is already in use, the calling go routine
// blocks until the mutex is available.
func (lm *LRWMutex) Lock() {
const isWriteLock = true
lm.lockLoop(context.Background(), lm.id, lm.source, math.MaxInt64, isWriteLock)
}
// GetLock tries to get a write lock on lm before the timeout occurs.
func (lm *LRWMutex) GetLock(ctx context.Context, id string, source string, timeout time.Duration) (locked bool) {
const isWriteLock = true
return lm.lockLoop(ctx, id, source, timeout, isWriteLock)
}
// RLock holds a read lock on lm.
//
// If one or more read lock are already in use, it will grant another lock.
// Otherwise the calling go routine blocks until the mutex is available.
func (lm *LRWMutex) RLock() {
const isWriteLock = false
lm.lockLoop(context.Background(), lm.id, lm.source, 1<<63-1, isWriteLock)
}
// GetRLock tries to get a read lock on lm before the timeout occurs.
func (lm *LRWMutex) GetRLock(ctx context.Context, id string, source string, timeout time.Duration) (locked bool) {
const isWriteLock = false
return lm.lockLoop(ctx, id, source, timeout, isWriteLock)
}
func (lm *LRWMutex) lock(id, source string, isWriteLock bool) (locked bool) {
lm.m.Lock()
lm.id = id
lm.source = source
if isWriteLock {
if lm.ref == 0 && !lm.isWriteLock {
lm.ref = 1
lm.isWriteLock = true
locked = true
}
} else {
if !lm.isWriteLock {
lm.ref++
locked = true
}
}
lm.m.Unlock()
return locked
}
const (
lockRetryInterval = 50 * time.Millisecond
)
// lockLoop will acquire either a read or a write lock
//
// The call will block until the lock is granted using a built-in
// timing randomized back-off algorithm to try again until successful
func (lm *LRWMutex) lockLoop(ctx context.Context, id, source string, timeout time.Duration, isWriteLock bool) (locked bool) {
r := rand.New(rand.NewSource(time.Now().UnixNano()))
retryCtx, cancel := context.WithTimeout(ctx, timeout)
defer cancel()
for {
select {
case <-retryCtx.Done():
// Caller context canceled or we timedout,
// return false anyways for both situations.
return false
default:
if lm.lock(id, source, isWriteLock) {
return true
}
time.Sleep(time.Duration(r.Float64() * float64(lockRetryInterval)))
}
}
}
// Unlock unlocks the write lock.
//
// It is a run-time error if lm is not locked on entry to Unlock.
func (lm *LRWMutex) Unlock() {
isWriteLock := true
success := lm.unlock(isWriteLock)
if !success {
panic("Trying to Unlock() while no Lock() is active")
}
}
// RUnlock releases a read lock held on lm.
//
// It is a run-time error if lm is not locked on entry to RUnlock.
func (lm *LRWMutex) RUnlock() {
isWriteLock := false
success := lm.unlock(isWriteLock)
if !success {
panic("Trying to RUnlock() while no RLock() is active")
}
}
func (lm *LRWMutex) unlock(isWriteLock bool) (unlocked bool) {
lm.m.Lock()
// Try to release lock.
if isWriteLock {
if lm.isWriteLock && lm.ref == 1 {
lm.ref = 0
lm.isWriteLock = false
unlocked = true
}
} else {
if !lm.isWriteLock {
if lm.ref > 0 {
lm.ref--
unlocked = true
}
}
}
lm.m.Unlock()
return unlocked
}
// ForceUnlock will forcefully clear a write or read lock.
func (lm *LRWMutex) ForceUnlock() {
lm.m.Lock()
lm.ref = 0
lm.isWriteLock = false
lm.m.Unlock()
}
// DRLocker returns a sync.Locker interface that implements
// the Lock and Unlock methods by calling drw.RLock and drw.RUnlock.
func (lm *LRWMutex) DRLocker() sync.Locker {
return (*drlocker)(lm)
}
type drlocker LRWMutex
func (dr *drlocker) Lock() { (*LRWMutex)(dr).RLock() }
func (dr *drlocker) Unlock() { (*LRWMutex)(dr).RUnlock() }