blob: 391f0b791020dfdf109d1b5d676b3965d6d5cff3 (
plain)
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
|
package ctxwatch
import (
"context"
)
// ContextWatcher watches a context and performs an action when the context is canceled. It can watch one context at a
// time.
type ContextWatcher struct {
onCancel func()
onUnwatchAfterCancel func()
unwatchChan chan struct{}
watchInProgress bool
onCancelWasCalled bool
}
// NewContextWatcher returns a ContextWatcher. onCancel will be called when a watched context is canceled.
// OnUnwatchAfterCancel will be called when Unwatch is called and the watched context had already been canceled and
// onCancel called.
func NewContextWatcher(onCancel func(), onUnwatchAfterCancel func()) *ContextWatcher {
cw := &ContextWatcher{
onCancel: onCancel,
onUnwatchAfterCancel: onUnwatchAfterCancel,
unwatchChan: make(chan struct{}),
}
return cw
}
// Watch starts watching ctx. If ctx is canceled then the onCancel function passed to NewContextWatcher will be called.
func (cw *ContextWatcher) Watch(ctx context.Context) {
if cw.watchInProgress {
panic("Watch already in progress")
}
cw.onCancelWasCalled = false
if ctx.Done() != nil {
cw.watchInProgress = true
go func() {
select {
case <-ctx.Done():
cw.onCancel()
cw.onCancelWasCalled = true
<-cw.unwatchChan
case <-cw.unwatchChan:
}
}()
} else {
cw.watchInProgress = false
}
}
// Unwatch stops watching the previously watched context. If the onCancel function passed to NewContextWatcher was
// called then onUnwatchAfterCancel will also be called.
func (cw *ContextWatcher) Unwatch() {
if cw.watchInProgress {
cw.unwatchChan <- struct{}{}
if cw.onCancelWasCalled {
cw.onUnwatchAfterCancel()
}
cw.watchInProgress = false
}
}
|
