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 14package lazy 15 16import ( 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// 27type onceMore struct { 28 mu sync.Mutex 29 lock uint32 30 done uint32 31} 32 33func (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 56func (t *onceMore) InProgress() bool { 57 return atomic.LoadUint32(&t.lock) == 1 58} 59 60func (t *onceMore) Done() bool { 61 return atomic.LoadUint32(&t.done) == 1 62} 63 64func (t *onceMore) ResetWithLock() *sync.Mutex { 65 t.mu.Lock() 66 defer atomic.StoreUint32(&t.done, 0) 67 return &t.mu 68} 69