once.go (1575B)
1 // Copyright 2019 The Hugo Authors. All rights reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 // http://www.apache.org/licenses/LICENSE-2.0
7 //
8 // Unless required by applicable law or agreed to in writing, software
9 // distributed under the License is distributed on an "AS IS" BASIS,
10 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11 // See the License for the specific language governing permissions and
12 // limitations under the License.
13
14 package lazy
15
16 import (
17 "sync"
18 "sync/atomic"
19 )
20
21 // onceMore is similar to sync.Once.
22 //
23 // Additional features are:
24 // * it can be reset, so the action can be repeated if needed
25 // * it has methods to check if it's done or in progress
26 //
27 type onceMore struct {
28 mu sync.Mutex
29 lock uint32
30 done uint32
31 }
32
33 func (t *onceMore) Do(f func()) {
34 if atomic.LoadUint32(&t.done) == 1 {
35 return
36 }
37
38 // f may call this Do and we would get a deadlock.
39 locked := atomic.CompareAndSwapUint32(&t.lock, 0, 1)
40 if !locked {
41 return
42 }
43 defer atomic.StoreUint32(&t.lock, 0)
44
45 t.mu.Lock()
46 defer t.mu.Unlock()
47
48 // Double check
49 if t.done == 1 {
50 return
51 }
52 defer atomic.StoreUint32(&t.done, 1)
53 f()
54 }
55
56 func (t *onceMore) InProgress() bool {
57 return atomic.LoadUint32(&t.lock) == 1
58 }
59
60 func (t *onceMore) Done() bool {
61 return atomic.LoadUint32(&t.done) == 1
62 }
63
64 func (t *onceMore) ResetWithLock() *sync.Mutex {
65 t.mu.Lock()
66 defer atomic.StoreUint32(&t.done, 0)
67 return &t.mu
68 }