mirror of
https://github.com/etcd-io/etcd.git
synced 2024-09-27 06:25:44 +00:00
113 lines
3.1 KiB
Go
113 lines
3.1 KiB
Go
// Copyright 2016 CoreOS, Inc.
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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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"sync"
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"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
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v3 "github.com/coreos/etcd/clientv3"
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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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client *v3.Client
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ctx context.Context
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pfx string
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myKey string
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myRev int64
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}
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func NewMutex(ctx context.Context, client *v3.Client, pfx string) *Mutex {
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return &Mutex{client, ctx, pfx, "", -1}
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}
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// Lock locks the mutex with a cancellable context. If the context is cancelled
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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, err := NewSession(m.client)
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if err != nil {
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return err
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}
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// put self in lock waiters via myKey; oldest waiter holds lock
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m.myKey, m.myRev, err = NewUniqueKey(ctx, m.client, m.pfx, v3.WithLease(s.Lease()))
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// wait for lock to become available
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for err == nil {
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// find oldest element in waiters via revision of insertion
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var resp *v3.GetResponse
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resp, err = m.client.Get(ctx, m.pfx, v3.WithFirstRev()...)
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if err != nil {
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break
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}
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if m.myRev == resp.Kvs[0].CreateRevision {
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// myKey is oldest in waiters; myKey holds the lock now
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return nil
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}
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// otherwise myKey isn't lowest, so there must be a pfx prior to myKey
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opts := append(v3.WithLastRev(), v3.WithRev(m.myRev-1))
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resp, err = m.client.Get(ctx, m.pfx, opts...)
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if err != nil {
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break
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}
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lastKey := string(resp.Kvs[0].Key)
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// wait for release on prior pfx
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err = waitUpdate(ctx, m.client, lastKey, v3.WithRev(m.myRev))
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// try again in case lastKey left the wait list before acquiring the lock;
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// myKey can only hold the lock if it's the oldest in the list
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}
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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()
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default:
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}
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return err
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}
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func (m *Mutex) Unlock() error {
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if _, err := m.client.Delete(m.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.CreatedRevision(m.myKey), "=", m.myRev)
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}
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func (m *Mutex) Key() string { return m.myKey }
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type lockerMutex struct{ *Mutex }
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func (lm *lockerMutex) Lock() {
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if err := lm.Mutex.Lock(lm.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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if err := lm.Mutex.Unlock(); 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(ctx context.Context, client *v3.Client, pfx string) sync.Locker {
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return &lockerMutex{NewMutex(ctx, client, pfx)}
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}
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