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
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
|
// Copyright 2011 The Go 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 sync_test
import (
"internal/race"
"runtime"
. "sync"
"sync/atomic"
"testing"
)
func testWaitGroup(t *testing.T, wg1 *WaitGroup, wg2 *WaitGroup) {
n := 16
wg1.Add(n)
wg2.Add(n)
exited := make(chan bool, n)
for i := 0; i != n; i++ {
go func(i int) {
wg1.Done()
wg2.Wait()
exited <- true
}(i)
}
wg1.Wait()
for i := 0; i != n; i++ {
select {
case <-exited:
t.Fatal("WaitGroup released group too soon")
default:
}
wg2.Done()
}
for i := 0; i != n; i++ {
<-exited // Will block if barrier fails to unlock someone.
}
}
func TestWaitGroup(t *testing.T) {
wg1 := &WaitGroup{}
wg2 := &WaitGroup{}
// Run the same test a few times to ensure barrier is in a proper state.
for i := 0; i != 8; i++ {
testWaitGroup(t, wg1, wg2)
}
}
func knownRacy(t *testing.T) {
if race.Enabled {
t.Skip("skipping known-racy test under the race detector")
}
}
func TestWaitGroupMisuse(t *testing.T) {
defer func() {
err := recover()
if err != "sync: negative WaitGroup counter" {
t.Fatalf("Unexpected panic: %#v", err)
}
}()
wg := &WaitGroup{}
wg.Add(1)
wg.Done()
wg.Done()
t.Fatal("Should panic")
}
func TestWaitGroupMisuse2(t *testing.T) {
knownRacy(t)
if testing.Short() {
t.Skip("skipping flaky test in short mode; see issue 11443")
}
if runtime.NumCPU() <= 2 {
t.Skip("NumCPU<=2, skipping: this test requires parallelism")
}
defer func() {
err := recover()
if err != "sync: negative WaitGroup counter" &&
err != "sync: WaitGroup misuse: Add called concurrently with Wait" &&
err != "sync: WaitGroup is reused before previous Wait has returned" {
t.Fatalf("Unexpected panic: %#v", err)
}
}()
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
done := make(chan interface{}, 2)
// The detection is opportunistically, so we want it to panic
// at least in one run out of a million.
for i := 0; i < 1e6; i++ {
var wg WaitGroup
wg.Add(1)
go func() {
defer func() {
done <- recover()
}()
wg.Wait()
}()
go func() {
defer func() {
done <- recover()
}()
wg.Add(1) // This is the bad guy.
wg.Done()
}()
wg.Done()
for j := 0; j < 2; j++ {
if err := <-done; err != nil {
panic(err)
}
}
}
t.Fatal("Should panic")
}
func TestWaitGroupMisuse3(t *testing.T) {
knownRacy(t)
if runtime.NumCPU() <= 1 {
t.Skip("NumCPU==1, skipping: this test requires parallelism")
}
defer func() {
err := recover()
if err != "sync: negative WaitGroup counter" &&
err != "sync: WaitGroup misuse: Add called concurrently with Wait" &&
err != "sync: WaitGroup is reused before previous Wait has returned" {
t.Fatalf("Unexpected panic: %#v", err)
}
}()
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
done := make(chan interface{}, 2)
// The detection is opportunistically, so we want it to panic
// at least in one run out of a million.
for i := 0; i < 1e6; i++ {
var wg WaitGroup
wg.Add(1)
go func() {
defer func() {
done <- recover()
}()
wg.Done()
}()
go func() {
defer func() {
done <- recover()
}()
wg.Wait()
// Start reusing the wg before waiting for the Wait below to return.
wg.Add(1)
go func() {
wg.Done()
}()
wg.Wait()
}()
wg.Wait()
for j := 0; j < 2; j++ {
if err := <-done; err != nil {
panic(err)
}
}
}
t.Fatal("Should panic")
}
func TestWaitGroupRace(t *testing.T) {
// Run this test for about 1ms.
for i := 0; i < 1000; i++ {
wg := &WaitGroup{}
n := new(int32)
// spawn goroutine 1
wg.Add(1)
go func() {
atomic.AddInt32(n, 1)
wg.Done()
}()
// spawn goroutine 2
wg.Add(1)
go func() {
atomic.AddInt32(n, 1)
wg.Done()
}()
// Wait for goroutine 1 and 2
wg.Wait()
if atomic.LoadInt32(n) != 2 {
t.Fatal("Spurious wakeup from Wait")
}
}
}
func TestWaitGroupAlign(t *testing.T) {
type X struct {
x byte
wg WaitGroup
}
var x X
x.wg.Add(1)
go func(x *X) {
x.wg.Done()
}(&x)
x.wg.Wait()
}
func BenchmarkWaitGroupUncontended(b *testing.B) {
type PaddedWaitGroup struct {
WaitGroup
pad [128]uint8
}
b.RunParallel(func(pb *testing.PB) {
var wg PaddedWaitGroup
for pb.Next() {
wg.Add(1)
wg.Done()
wg.Wait()
}
})
}
func benchmarkWaitGroupAddDone(b *testing.B, localWork int) {
var wg WaitGroup
b.RunParallel(func(pb *testing.PB) {
foo := 0
for pb.Next() {
wg.Add(1)
for i := 0; i < localWork; i++ {
foo *= 2
foo /= 2
}
wg.Done()
}
_ = foo
})
}
func BenchmarkWaitGroupAddDone(b *testing.B) {
benchmarkWaitGroupAddDone(b, 0)
}
func BenchmarkWaitGroupAddDoneWork(b *testing.B) {
benchmarkWaitGroupAddDone(b, 100)
}
func benchmarkWaitGroupWait(b *testing.B, localWork int) {
var wg WaitGroup
b.RunParallel(func(pb *testing.PB) {
foo := 0
for pb.Next() {
wg.Wait()
for i := 0; i < localWork; i++ {
foo *= 2
foo /= 2
}
}
_ = foo
})
}
func BenchmarkWaitGroupWait(b *testing.B) {
benchmarkWaitGroupWait(b, 0)
}
func BenchmarkWaitGroupWaitWork(b *testing.B) {
benchmarkWaitGroupWait(b, 100)
}
func BenchmarkWaitGroupActuallyWait(b *testing.B) {
b.ReportAllocs()
b.RunParallel(func(pb *testing.PB) {
for pb.Next() {
var wg WaitGroup
wg.Add(1)
go func() {
wg.Done()
}()
wg.Wait()
}
})
}
|
