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rwmutex.go
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rwmutex.go
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// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package recipe
import (
v3 "github.com/coreos/etcd/clientv3"
"github.com/coreos/etcd/mvcc/mvccpb"
"golang.org/x/net/context"
)
type RWMutex struct {
client *v3.Client
ctx context.Context
key string
myKey *EphemeralKV
}
func NewRWMutex(client *v3.Client, key string) *RWMutex {
return &RWMutex{client, context.TODO(), key, nil}
}
func (rwm *RWMutex) RLock() error {
rk, err := NewUniqueEphemeralKey(rwm.client, rwm.key+"/read")
if err != nil {
return err
}
rwm.myKey = rk
// if there are nodes with "write-" and a lower
// revision number than us we must wait
resp, err := rwm.client.Get(rwm.ctx, rwm.key+"/write", v3.WithFirstRev()...)
if err != nil {
return err
}
if len(resp.Kvs) == 0 || resp.Kvs[0].ModRevision > rk.Revision() {
// no blocking since no write key
return nil
}
return rwm.waitOnLowest()
}
func (rwm *RWMutex) Lock() error {
rk, err := NewUniqueEphemeralKey(rwm.client, rwm.key+"/write")
if err != nil {
return err
}
rwm.myKey = rk
for {
// find any key of lower rev number blocks the write lock
opts := append(v3.WithLastRev(), v3.WithRev(rk.Revision()-1))
resp, err := rwm.client.Get(rwm.ctx, rwm.key, opts...)
if err != nil {
return err
}
if len(resp.Kvs) == 0 {
// no matching for revision before myKey; acquired
break
}
if err := rwm.waitOnLowest(); err != nil {
return err
}
// get the new lowest, etc until this is the only one left
}
return nil
}
func (rwm *RWMutex) waitOnLowest() error {
// must block; get key before ek for waiting
opts := append(v3.WithLastRev(), v3.WithRev(rwm.myKey.Revision()-1))
lastKey, err := rwm.client.Get(rwm.ctx, rwm.key, opts...)
if err != nil {
return err
}
// wait for release on prior key
_, err = WaitEvents(
rwm.client,
string(lastKey.Kvs[0].Key),
rwm.myKey.Revision(),
[]mvccpb.Event_EventType{mvccpb.DELETE})
return err
}
func (rwm *RWMutex) RUnlock() error { return rwm.myKey.Delete() }
func (rwm *RWMutex) Unlock() error { return rwm.myKey.Delete() }