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
|
// Copyright 2018 Google 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 tmutex provides the implementation of a mutex that implements an
// efficient TryLock function in addition to Lock and Unlock.
package tmutex
import (
"sync/atomic"
)
// Mutex is a mutual exclusion primitive that implements TryLock in addition
// to Lock and Unlock.
type Mutex struct {
v int32
ch chan struct{}
}
// Init initializes the mutex.
func (m *Mutex) Init() {
m.v = 1
m.ch = make(chan struct{}, 1)
}
// Lock acquires the mutex. If it is currently held by another goroutine, Lock
// will wait until it has a chance to acquire it.
func (m *Mutex) Lock() {
// Uncontended case.
if atomic.AddInt32(&m.v, -1) == 0 {
return
}
for {
// Try to acquire the mutex again, at the same time making sure
// that m.v is negative, which indicates to the owner of the
// lock that it is contended, which will force it to try to wake
// someone up when it releases the mutex.
if v := atomic.LoadInt32(&m.v); v >= 0 && atomic.SwapInt32(&m.v, -1) == 1 {
return
}
// Wait for the mutex to be released before trying again.
<-m.ch
}
}
// TryLock attempts to acquire the mutex without blocking. If the mutex is
// currently held by another goroutine, it fails to acquire it and returns
// false.
func (m *Mutex) TryLock() bool {
v := atomic.LoadInt32(&m.v)
if v <= 0 {
return false
}
return atomic.CompareAndSwapInt32(&m.v, 1, 0)
}
// Unlock releases the mutex.
func (m *Mutex) Unlock() {
if atomic.SwapInt32(&m.v, 1) == 0 {
// There were no pending waiters.
return
}
// Wake some waiter up.
select {
case m.ch <- struct{}{}:
default:
}
}
|
