/
latch.go
62 lines (53 loc) · 1.64 KB
/
latch.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
// Copyright 2021 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package scheduler
import (
"sync"
"github.com/pingcap/errors"
)
// latches provides a simple way to block concurrent accessing to one resource, if caller tries to acquire latch before
// accessing resources.
type latches struct {
mu sync.Mutex
inUse map[string]struct{}
// TODO: use map[string]semaphore to implement a blocking acquire
}
// ReleaseFunc wraps on releasing a latch.
// It is safe to call multiple times. Also compiler can warn you of not used ReleaseFunc variables.
type ReleaseFunc func()
func newLatches() *latches {
return &latches{
inUse: map[string]struct{}{},
}
}
func (l *latches) tryAcquire(name string) (ReleaseFunc, error) {
l.mu.Lock()
defer l.mu.Unlock()
if _, ok := l.inUse[name]; ok {
return nil, errors.Errorf("latch %s is in use by other client", name)
}
l.inUse[name] = struct{}{}
var once sync.Once
return func() {
once.Do(func() {
l.release(name)
})
}, nil
}
// release should not be called directly, it's recommended to wrap it with ReleaseFunc to avoid release a latch that not
// belongs to caller.
func (l *latches) release(name string) {
l.mu.Lock()
delete(l.inUse, name)
l.mu.Unlock()
}