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
|
// Copyright (c) 2011 - Gustavo Niemeyer <gustavo@niemeyer.net>
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// * Neither the name of the copyright holder nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// The tomb package handles clean goroutine tracking and termination.
//
// The zero value of a Tomb is ready to handle the creation of a tracked
// goroutine via its Go method, and then any tracked goroutine may call
// the Go method again to create additional tracked goroutines at
// any point.
//
// If any of the tracked goroutines returns a non-nil error, or the
// Kill or Killf method is called by any goroutine in the system (tracked
// or not), the tomb Err is set, Alive is set to false, and the Dying
// channel is closed to flag that all tracked goroutines are supposed
// to willingly terminate as soon as possible.
//
// Once all tracked goroutines terminate, the Dead channel is closed,
// and Wait unblocks and returns the first non-nil error presented
// to the tomb via a result or an explicit Kill or Killf method call,
// or nil if there were no errors.
//
// It is okay to create further goroutines via the Go method while
// the tomb is in a dying state. The final dead state is only reached
// once all tracked goroutines terminate, at which point calling
// the Go method again will cause a runtime panic.
//
// Tracked functions and methods that are still running while the tomb
// is in dying state may choose to return ErrDying as their error value.
// This preserves the well established non-nil error convention, but is
// understood by the tomb as a clean termination. The Err and Wait
// methods will still return nil if all observed errors were either
// nil or ErrDying.
//
// For background and a detailed example, see the following blog post:
//
// http://blog.labix.org/2011/10/09/death-of-goroutines-under-control
//
package tomb
import (
"errors"
"fmt"
"sync"
)
// A Tomb tracks the lifecycle of one or more goroutines as alive,
// dying or dead, and the reason for their death.
//
// See the package documentation for details.
type Tomb struct {
m sync.Mutex
alive int
dying chan struct{}
dead chan struct{}
reason error
}
var (
ErrStillAlive = errors.New("tomb: still alive")
ErrDying = errors.New("tomb: dying")
)
func (t *Tomb) init() {
t.m.Lock()
if t.dead == nil {
t.dead = make(chan struct{})
t.dying = make(chan struct{})
t.reason = ErrStillAlive
}
t.m.Unlock()
}
// Dead returns the channel that can be used to wait until
// all goroutines have finished running.
func (t *Tomb) Dead() <-chan struct{} {
t.init()
return t.dead
}
// Dying returns the channel that can be used to wait until
// t.Kill is called.
func (t *Tomb) Dying() <-chan struct{} {
t.init()
return t.dying
}
// Wait blocks until all goroutines have finished running, and
// then returns the reason for their death.
func (t *Tomb) Wait() error {
t.init()
<-t.dead
t.m.Lock()
reason := t.reason
t.m.Unlock()
return reason
}
// Go runs f in a new goroutine and tracks its termination.
//
// If f returns a non-nil error, t.Kill is called with that
// error as the death reason parameter.
//
// It is f's responsibility to monitor the tomb and return
// appropriately once it is in a dying state.
//
// It is safe for the f function to call the Go method again
// to create additional tracked goroutines. Once all tracked
// goroutines return, the Dead channel is closed and the
// Wait method unblocks and returns the death reason.
//
// Calling the Go method after all tracked goroutines return
// causes a runtime panic. For that reason, calling the Go
// method a second time out of a tracked goroutine is unsafe.
func (t *Tomb) Go(f func() error) {
t.init()
t.m.Lock()
defer t.m.Unlock()
select {
case <-t.dead:
panic("tomb.Go called after all goroutines terminated")
default:
}
t.alive++
go t.run(f)
}
func (t *Tomb) run(f func() error) {
err := f()
t.m.Lock()
defer t.m.Unlock()
t.alive--
if t.alive == 0 || err != nil {
t.kill(err)
if t.alive == 0 {
close(t.dead)
}
}
}
// Kill puts the tomb in a dying state for the given reason,
// closes the Dying channel, and sets Alive to false.
//
// Althoguh Kill may be called multiple times, only the first
// non-nil error is recorded as the death reason.
//
// If reason is ErrDying, the previous reason isn't replaced
// even if nil. It's a runtime error to call Kill with ErrDying
// if t is not in a dying state.
func (t *Tomb) Kill(reason error) {
t.init()
t.m.Lock()
defer t.m.Unlock()
t.kill(reason)
}
func (t *Tomb) kill(reason error) {
if reason == ErrStillAlive {
panic("tomb: Kill with ErrStillAlive")
}
if reason == ErrDying {
if t.reason == ErrStillAlive {
panic("tomb: Kill with ErrDying while still alive")
}
return
}
if t.reason == ErrStillAlive {
t.reason = reason
close(t.dying)
return
}
if t.reason == nil {
t.reason = reason
return
}
}
// Killf calls the Kill method with an error built providing the received
// parameters to fmt.Errorf. The generated error is also returned.
func (t *Tomb) Killf(f string, a ...interface{}) error {
err := fmt.Errorf(f, a...)
t.Kill(err)
return err
}
// Err returns the death reason, or ErrStillAlive if the tomb
// is not in a dying or dead state.
func (t *Tomb) Err() (reason error) {
t.init()
t.m.Lock()
reason = t.reason
t.m.Unlock()
return
}
// Alive returns true if the tomb is not in a dying or dead state.
func (t *Tomb) Alive() bool {
return t.Err() == ErrStillAlive
}
|
