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
|
// Copyright 2016 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 errgroup provides synchronization, error propagation, and Context
// cancelation for groups of goroutines working on subtasks of a common task.
//
// [errgroup.Group] is related to [sync.WaitGroup] but adds handling of tasks
// returning errors.
package errgroup
import (
"context"
"fmt"
"sync"
)
type token struct{}
// A Group is a collection of goroutines working on subtasks that are part of
// the same overall task. A Group should not be reused for different tasks.
//
// A zero Group is valid, has no limit on the number of active goroutines,
// and does not cancel on error.
type Group struct {
cancel func(error)
wg sync.WaitGroup
sem chan token
errOnce sync.Once
err error
}
func (g *Group) done() {
if g.sem != nil {
<-g.sem
}
g.wg.Done()
}
// WithContext returns a new Group and an associated Context derived from ctx.
//
// The derived Context is canceled the first time a function passed to Go
// returns a non-nil error or the first time Wait returns, whichever occurs
// first.
func WithContext(ctx context.Context) (*Group, context.Context) {
ctx, cancel := context.WithCancelCause(ctx)
return &Group{cancel: cancel}, ctx
}
// Wait blocks until all function calls from the Go method have returned, then
// returns the first non-nil error (if any) from them.
func (g *Group) Wait() error {
g.wg.Wait()
if g.cancel != nil {
g.cancel(g.err)
}
return g.err
}
// Go calls the given function in a new goroutine.
//
// The first call to Go must happen before a Wait.
// It blocks until the new goroutine can be added without the number of
// goroutines in the group exceeding the configured limit.
//
// The first goroutine in the group that returns a non-nil error will
// cancel the associated Context, if any. The error will be returned
// by Wait.
func (g *Group) Go(f func() error) {
if g.sem != nil {
g.sem <- token{}
}
g.wg.Add(1)
go func() {
defer g.done()
// It is tempting to propagate panics from f()
// up to the goroutine that calls Wait, but
// it creates more problems than it solves:
// - it delays panics arbitrarily,
// making bugs harder to detect;
// - it turns f's panic stack into a mere value,
// hiding it from crash-monitoring tools;
// - it risks deadlocks that hide the panic entirely,
// if f's panic leaves the program in a state
// that prevents the Wait call from being reached.
// See #53757, #74275, #74304, #74306.
if err := f(); err != nil {
g.errOnce.Do(func() {
g.err = err
if g.cancel != nil {
g.cancel(g.err)
}
})
}
}()
}
// TryGo calls the given function in a new goroutine only if the number of
// active goroutines in the group is currently below the configured limit.
//
// The return value reports whether the goroutine was started.
func (g *Group) TryGo(f func() error) bool {
if g.sem != nil {
select {
case g.sem <- token{}:
// Note: this allows barging iff channels in general allow barging.
default:
return false
}
}
g.wg.Add(1)
go func() {
defer g.done()
if err := f(); err != nil {
g.errOnce.Do(func() {
g.err = err
if g.cancel != nil {
g.cancel(g.err)
}
})
}
}()
return true
}
// SetLimit limits the number of active goroutines in this group to at most n.
// A negative value indicates no limit.
// A limit of zero will prevent any new goroutines from being added.
//
// Any subsequent call to the Go method will block until it can add an active
// goroutine without exceeding the configured limit.
//
// The limit must not be modified while any goroutines in the group are active.
func (g *Group) SetLimit(n int) {
if n < 0 {
g.sem = nil
return
}
if len(g.sem) != 0 {
panic(fmt.Errorf("errgroup: modify limit while %v goroutines in the group are still active", len(g.sem)))
}
g.sem = make(chan token, n)
}
|
