-
Notifications
You must be signed in to change notification settings - Fork 777
/
fswatch.go
81 lines (71 loc) · 2.5 KB
/
fswatch.go
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
// Copyright 2022 Google LLC All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package fswatch provies Watch(), a utility function to watch a filesystem path.
package fswatch
import (
"time"
"github.com/sirupsen/logrus"
"gopkg.in/fsnotify.v1"
)
// Watch watches the filesystem path `path`. When anything changes, changes are
// batched for the period `batchFor`, then `processEvent` is called.
//
// Returns a cancel() function to terminate the watch.
func Watch(logger *logrus.Entry, path string, batchFor time.Duration, processEvent func()) (func(), error) {
logger = logger.WithField("path", path)
watcher, err := fsnotify.NewWatcher()
if err != nil {
return nil, err
}
cancelChan := make(chan struct{})
cancel := func() {
close(cancelChan)
_ = watcher.Close()
}
if err := watcher.Add(path); err != nil {
cancel()
return nil, err
}
go batchWatch(batchFor, watcher.Events, watcher.Errors, cancelChan, processEvent, func(error) {
logger.WithError(err).Errorf("error watching path")
})
return cancel, nil
}
// batchWatch: watch for events; when an event occurs, keep draining events for duration `batchFor`, then call processEvent().
// Intended for batching of rapid-fire events where we want to process the batch once, like filesystem update notifications.
func batchWatch(batchFor time.Duration, events chan fsnotify.Event, errors chan error, cancelChan chan struct{}, processEvent func(), onError func(error)) {
// Pattern shamelessly stolen from https://blog.gopheracademy.com/advent-2013/day-24-channel-buffering-patterns/
timer := time.NewTimer(0)
var timerCh <-chan time.Time
for {
select {
// start a timer when an event occurs, otherwise ignore event
case <-events:
if timerCh == nil {
timer.Reset(batchFor)
timerCh = timer.C
}
// on timer, run the batch; nil channels are silently ignored
case <-timerCh:
processEvent()
timerCh = nil
// handle errors
case err := <-errors:
onError(err)
// on cancel, abort
case <-cancelChan:
return
}
}
}