1 // Copyright 2016 The etcd Authors 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 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package recipe 16 17 import ( 18 "context" 19 20 "go.etcd.io/etcd/api/v3/mvccpb" 21 v3 "go.etcd.io/etcd/client/v3" 22 ) 23 24 // Barrier creates a key in etcd to block processes, then deletes the key to 25 // release all blocked processes. 26 type Barrier struct { 27 client *v3.Client 28 ctx context.Context 29 30 key string 31 } 32 33 func NewBarrier(client *v3.Client, key string) *Barrier { 34 return &Barrier{client, context.TODO(), key} 35 } 36 37 // Hold creates the barrier key causing processes to block on Wait. 38 func (b *Barrier) Hold() error { 39 _, err := newKey(b.client, b.key, v3.NoLease) 40 return err 41 } 42 43 // Release deletes the barrier key to unblock all waiting processes. 44 func (b *Barrier) Release() error { 45 _, err := b.client.Delete(b.ctx, b.key) 46 return err 47 } 48 49 // Wait blocks on the barrier key until it is deleted. If there is no key, Wait 50 // assumes Release has already been called and returns immediately. 51 func (b *Barrier) Wait() error { 52 resp, err := b.client.Get(b.ctx, b.key) 53 if err != nil { 54 return err 55 } 56 if len(resp.Kvs) == 0 { 57 // key already removed 58 return nil 59 } 60 _, err = WaitEvents( 61 b.client, 62 b.key, 63 resp.Header.Revision, 64 []mvccpb.Event_EventType{mvccpb.PUT, mvccpb.DELETE}) 65 return err 66 } 67