95 lines
2.4 KiB
Go
95 lines
2.4 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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"github.com/coreos/etcd/storage/storagepb"
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)
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type RWMutex 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 NewRWMutex(client *EtcdClient, key string) *RWMutex {
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return &RWMutex{client, key, nil}
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}
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func (rwm *RWMutex) RLock() error {
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// XXX: make reads ephemeral locks?
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rk, err := NewUniqueKey(rwm.client, rwm.key+"/read")
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if err != nil {
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return err
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}
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rwm.myKey = rk
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// if there are nodes with "write-" and a lower
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// revision number than us we must wait
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resp, err := NewRange(rwm.client, rwm.key+"/write").FirstRev()
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if err != nil {
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return err
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}
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if len(resp.Kvs) == 0 || resp.Kvs[0].ModRevision > rk.Revision() {
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// no blocking since no write key
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return nil
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}
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return rwm.waitOnLowest()
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}
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func (rwm *RWMutex) Lock() error {
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rk, err := NewUniqueKey(rwm.client, rwm.key+"/write")
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if err != nil {
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return err
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}
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rwm.myKey = rk
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for {
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// any key of lower rev number blocks the write lock
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resp, err := NewRangeRev(rwm.client, rwm.key, rk.Revision()-1).LastRev()
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if err != nil {
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return err
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}
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if len(resp.Kvs) == 0 {
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// no matching for revision before myKey; acquired
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return nil
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}
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if err := rwm.waitOnLowest(); err != nil {
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return err
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}
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// get the new lowest, etc until this is the only one left
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}
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return nil
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}
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func (rwm *RWMutex) waitOnLowest() error {
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// must block; get key before ek for waiting
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lastKey, err := NewRangeRev(rwm.client, rwm.key, rwm.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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rwm.client,
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string(lastKey.Kvs[0].Key),
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rwm.myKey.Revision(),
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[]storagepb.Event_EventType{storagepb.DELETE})
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return err
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}
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func (rwm *RWMutex) RUnlock() error { return rwm.myKey.Delete() }
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func (rwm *RWMutex) Unlock() error { return rwm.myKey.Delete() }
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