86 lines
2.1 KiB
Go
86 lines
2.1 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 recipe
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import (
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"sync"
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"github.com/coreos/etcd/storage/storagepb"
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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 *EtcdClient
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key string
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myKey *RemoteKV
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}
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func NewMutex(client *EtcdClient, key string) *Mutex {
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return &Mutex{client, key, nil}
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}
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func (m *Mutex) Lock() (err error) {
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// put self in lock waiters via myKey; oldest waiter holds lock
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m.myKey, err = NewUniqueKey(m.client, m.key)
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if err != nil {
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return err
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}
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// find oldest element in waiters via revision of insertion
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resp, err := NewRange(m.client, m.key).FirstRev()
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if err != nil {
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return err
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}
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// if myKey is oldest in waiters, then myKey holds the lock
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if m.myKey.Revision() == resp.Kvs[0].CreateRevision {
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return nil
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}
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// otherwise myKey isn't lowest, so there must be a key prior to myKey
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lastKey, err := NewRangeRev(m.client, m.key, m.myKey.Revision()-1).LastRev()
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if err != nil {
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return err
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}
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// wait for release on prior key
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_, err = WaitEvents(
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m.client,
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string(lastKey.Kvs[0].Key),
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m.myKey.Revision()-1,
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[]storagepb.Event_EventType{storagepb.DELETE})
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// myKey now oldest
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return err
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}
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func (m *Mutex) Unlock() error {
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err := m.myKey.Delete()
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m.myKey = nil
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return err
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}
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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(); 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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func NewLocker(client *EtcdClient, key string) sync.Locker {
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return &lockerMutex{NewMutex(client, key)}
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}
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