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 15package concurrency 16 17import ( 18 "context" 19 "fmt" 20 "sync" 21 22 v3 "go.etcd.io/etcd/clientv3" 23 pb "go.etcd.io/etcd/etcdserver/etcdserverpb" 24) 25 26// Mutex implements the sync Locker interface with etcd 27type Mutex struct { 28 s *Session 29 30 pfx string 31 myKey string 32 myRev int64 33 hdr *pb.ResponseHeader 34} 35 36func NewMutex(s *Session, pfx string) *Mutex { 37 return &Mutex{s, pfx + "/", "", -1, nil} 38} 39 40// Lock locks the mutex with a cancelable context. If the context is canceled 41// while trying to acquire the lock, the mutex tries to clean its stale lock entry. 42func (m *Mutex) Lock(ctx context.Context) error { 43 s := m.s 44 client := m.s.Client() 45 46 m.myKey = fmt.Sprintf("%s%x", m.pfx, s.Lease()) 47 cmp := v3.Compare(v3.CreateRevision(m.myKey), "=", 0) 48 // put self in lock waiters via myKey; oldest waiter holds lock 49 put := v3.OpPut(m.myKey, "", v3.WithLease(s.Lease())) 50 // reuse key in case this session already holds the lock 51 get := v3.OpGet(m.myKey) 52 // fetch current holder to complete uncontended path with only one RPC 53 getOwner := v3.OpGet(m.pfx, v3.WithFirstCreate()...) 54 resp, err := client.Txn(ctx).If(cmp).Then(put, getOwner).Else(get, getOwner).Commit() 55 if err != nil { 56 return err 57 } 58 m.myRev = resp.Header.Revision 59 if !resp.Succeeded { 60 m.myRev = resp.Responses[0].GetResponseRange().Kvs[0].CreateRevision 61 } 62 // if no key on prefix / the minimum rev is key, already hold the lock 63 ownerKey := resp.Responses[1].GetResponseRange().Kvs 64 if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev { 65 m.hdr = resp.Header 66 return nil 67 } 68 69 // wait for deletion revisions prior to myKey 70 hdr, werr := waitDeletes(ctx, client, m.pfx, m.myRev-1) 71 // release lock key if wait failed 72 if werr != nil { 73 m.Unlock(client.Ctx()) 74 } else { 75 m.hdr = hdr 76 } 77 return werr 78} 79 80func (m *Mutex) Unlock(ctx context.Context) error { 81 client := m.s.Client() 82 if _, err := client.Delete(ctx, m.myKey); err != nil { 83 return err 84 } 85 m.myKey = "\x00" 86 m.myRev = -1 87 return nil 88} 89 90func (m *Mutex) IsOwner() v3.Cmp { 91 return v3.Compare(v3.CreateRevision(m.myKey), "=", m.myRev) 92} 93 94func (m *Mutex) Key() string { return m.myKey } 95 96// Header is the response header received from etcd on acquiring the lock. 97func (m *Mutex) Header() *pb.ResponseHeader { return m.hdr } 98 99type lockerMutex struct{ *Mutex } 100 101func (lm *lockerMutex) Lock() { 102 client := lm.s.Client() 103 if err := lm.Mutex.Lock(client.Ctx()); err != nil { 104 panic(err) 105 } 106} 107func (lm *lockerMutex) Unlock() { 108 client := lm.s.Client() 109 if err := lm.Mutex.Unlock(client.Ctx()); err != nil { 110 panic(err) 111 } 112} 113 114// NewLocker creates a sync.Locker backed by an etcd mutex. 115func NewLocker(s *Session, pfx string) sync.Locker { 116 return &lockerMutex{NewMutex(s, pfx)} 117} 118