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
|
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package syncs contains additional sync types and functionality.
package syncs
import (
"context"
"sync/atomic"
)
// ClosedChan returns a channel that's already closed.
func ClosedChan() <-chan struct{} { return closedChan }
var closedChan = initClosedChan()
func initClosedChan() <-chan struct{} {
ch := make(chan struct{})
close(ch)
return ch
}
// WaitGroupChan is like a sync.WaitGroup, but has a chan that closes
// on completion that you can wait on. (This, you can only use the
// value once)
// Also, its zero value is not usable. Use the constructor.
type WaitGroupChan struct {
n int64 // atomic
done chan struct{} // closed on transition to zero
}
// NewWaitGroupChan returns a new single-use WaitGroupChan.
func NewWaitGroupChan() *WaitGroupChan {
return &WaitGroupChan{done: make(chan struct{})}
}
// DoneChan returns a channel that's closed on completion.
func (wg *WaitGroupChan) DoneChan() <-chan struct{} { return wg.done }
// Add adds delta, which may be negative, to the WaitGroupChan
// counter. If the counter becomes zero, all goroutines blocked on
// Wait or the Done chan are released. If the counter goes negative,
// Add panics.
//
// Note that calls with a positive delta that occur when the counter
// is zero must happen before a Wait. Calls with a negative delta, or
// calls with a positive delta that start when the counter is greater
// than zero, may happen at any time. Typically this means the calls
// to Add should execute before the statement creating the goroutine
// or other event to be waited for.
func (wg *WaitGroupChan) Add(delta int) {
n := atomic.AddInt64(&wg.n, int64(delta))
if n == 0 {
close(wg.done)
}
}
// Decr decrements the WaitGroup counter by one.
//
// (It is like sync.WaitGroup's Done method, but we don't use Done in
// this type, because it's ambiguous between Context.Done and
// WaitGroup.Done. So we use DoneChan and Decr instead.)
func (wg *WaitGroupChan) Decr() {
wg.Add(-1)
}
// Wait blocks until the WaitGroupChan counter is zero.
func (wg *WaitGroupChan) Wait() { <-wg.done }
// AtomicBool is an atomic boolean.
type AtomicBool int32
func (b *AtomicBool) Set(v bool) {
var n int32
if v {
n = 1
}
atomic.StoreInt32((*int32)(b), n)
}
// Swap sets b to v and reports whether it changed.
func (b *AtomicBool) Swap(v bool) (changed bool) {
var n int32
if v {
n = 1
}
old := atomic.SwapInt32((*int32)(b), n)
return old != n
}
func (b *AtomicBool) Get() bool {
return atomic.LoadInt32((*int32)(b)) != 0
}
// AtomicUint32 is an atomic uint32.
type AtomicUint32 uint32
func (b *AtomicUint32) Set(v uint32) {
atomic.StoreUint32((*uint32)(b), v)
}
func (b *AtomicUint32) Get() uint32 {
return atomic.LoadUint32((*uint32)(b))
}
// Semaphore is a counting semaphore.
//
// Use NewSemaphore to create one.
type Semaphore struct {
c chan struct{}
}
// NewSemaphore returns a semaphore with resource count n.
func NewSemaphore(n int) Semaphore {
return Semaphore{c: make(chan struct{}, n)}
}
// Acquire blocks until a resource is acquired.
func (s Semaphore) Acquire() {
s.c <- struct{}{}
}
// AcquireContext reports whether the resource was acquired before the ctx was done.
func (s Semaphore) AcquireContext(ctx context.Context) bool {
select {
case s.c <- struct{}{}:
return true
case <-ctx.Done():
return false
}
}
// TryAcquire reports, without blocking, whether the resource was acquired.
func (s Semaphore) TryAcquire() bool {
select {
case s.c <- struct{}{}:
return true
default:
return false
}
}
// Release releases a resource.
func (s Semaphore) Release() {
<-s.c
}
|
