blob: 013534193ea578a348f0c2fc2bf20da317d1c52b [file] [log] [blame]
Stephane Barbarie260a5632019-02-26 16:12:49 -05001// 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}