mirror of
https://github.com/etcd-io/etcd.git
synced 2024-09-27 06:25:44 +00:00
119 lines
3.2 KiB
Go
119 lines
3.2 KiB
Go
// Copyright 2016 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package concurrency
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import (
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"context"
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"fmt"
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"sync"
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v3 "github.com/coreos/etcd/clientv3"
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pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
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)
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// Mutex implements the sync Locker interface with etcd
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type Mutex struct {
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s *Session
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pfx string
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myKey string
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myRev int64
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hdr *pb.ResponseHeader
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}
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func NewMutex(s *Session, pfx string) *Mutex {
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return &Mutex{s, pfx + "/", "", -1, nil}
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}
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// Lock locks the mutex with a cancelable context. If the context is canceled
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// while trying to acquire the lock, the mutex tries to clean its stale lock entry.
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func (m *Mutex) Lock(ctx context.Context) error {
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s := m.s
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client := m.s.Client()
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m.myKey = fmt.Sprintf("%s%x", m.pfx, s.Lease())
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cmp := v3.Compare(v3.CreateRevision(m.myKey), "=", 0)
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// put self in lock waiters via myKey; oldest waiter holds lock
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put := v3.OpPut(m.myKey, "", v3.WithLease(s.Lease()))
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// reuse key in case this session already holds the lock
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get := v3.OpGet(m.myKey)
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// fetch current holder to complete uncontended path with only one RPC
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getOwner := v3.OpGet(m.pfx, v3.WithFirstCreate()...)
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resp, err := client.Txn(ctx).If(cmp).Then(put, getOwner).Else(get, getOwner).Commit()
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if err != nil {
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return err
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}
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m.myRev = resp.Header.Revision
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if !resp.Succeeded {
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m.myRev = resp.Responses[0].GetResponseRange().Kvs[0].CreateRevision
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}
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// if no key on prefix / the minimum rev is key, already hold the lock
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ownerKey := resp.Responses[1].GetResponseRange().Kvs
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if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev {
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m.hdr = resp.Header
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return nil
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}
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// wait for deletion revisions prior to myKey
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hdr, werr := waitDeletes(ctx, client, m.pfx, m.myRev-1)
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// release lock key if cancelled
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select {
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case <-ctx.Done():
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m.Unlock(client.Ctx())
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default:
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m.hdr = hdr
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}
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return werr
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}
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func (m *Mutex) Unlock(ctx context.Context) error {
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client := m.s.Client()
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if _, err := client.Delete(ctx, m.myKey); err != nil {
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return err
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}
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m.myKey = "\x00"
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m.myRev = -1
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return nil
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}
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func (m *Mutex) IsOwner() v3.Cmp {
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return v3.Compare(v3.CreateRevision(m.myKey), "=", m.myRev)
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}
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func (m *Mutex) Key() string { return m.myKey }
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// Header is the response header received from etcd on acquiring the lock.
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func (m *Mutex) Header() *pb.ResponseHeader { return m.hdr }
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type lockerMutex struct{ *Mutex }
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func (lm *lockerMutex) Lock() {
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client := lm.s.Client()
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if err := lm.Mutex.Lock(client.Ctx()); err != nil {
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panic(err)
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}
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}
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func (lm *lockerMutex) Unlock() {
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client := lm.s.Client()
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if err := lm.Mutex.Unlock(client.Ctx()); err != nil {
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panic(err)
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}
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}
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// NewLocker creates a sync.Locker backed by an etcd mutex.
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func NewLocker(s *Session, pfx string) sync.Locker {
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return &lockerMutex{NewMutex(s, pfx)}
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}
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