minio/cmd/local-locker.go

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/*
* Minio Cloud Storage, (C) 2018 Minio, Inc.
*
* 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 cmd
import (
"fmt"
"sync"
"time"
"github.com/minio/dsync"
)
// lockRequesterInfo stores various info from the client for each lock that is requested.
type lockRequesterInfo struct {
writer bool // Bool whether write or read lock.
node string // Network address of client claiming lock.
serviceEndpoint string // RPC path of client claiming lock.
uid string // UID to uniquely identify request of client.
timestamp time.Time // Timestamp set at the time of initialization.
timeLastCheck time.Time // Timestamp for last check of validity of lock.
}
// isWriteLock returns whether the lock is a write or read lock.
func isWriteLock(lri []lockRequesterInfo) bool {
return len(lri) == 1 && lri[0].writer
}
// localLocker implements Dsync.NetLocker
type localLocker struct {
mutex sync.Mutex
serviceEndpoint string
serverAddr string
lockMap map[string][]lockRequesterInfo
}
func (l *localLocker) ServerAddr() string {
return l.serverAddr
}
func (l *localLocker) ServiceEndpoint() string {
return l.serviceEndpoint
}
func (l *localLocker) Lock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
_, isLockTaken := l.lockMap[args.Resource]
if !isLockTaken { // No locks held on the given name, so claim write lock
l.lockMap[args.Resource] = []lockRequesterInfo{
{
writer: true,
node: args.ServerAddr,
serviceEndpoint: args.ServiceEndpoint,
uid: args.UID,
timestamp: UTCNow(),
timeLastCheck: UTCNow(),
},
}
}
// return reply=true if lock was granted.
return !isLockTaken, nil
}
func (l *localLocker) Unlock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
var lri []lockRequesterInfo
if lri, reply = l.lockMap[args.Resource]; !reply {
// No lock is held on the given name
return reply, fmt.Errorf("Unlock attempted on an unlocked entity: %s", args.Resource)
}
if reply = isWriteLock(lri); !reply {
// Unless it is a write lock
return reply, fmt.Errorf("Unlock attempted on a read locked entity: %s (%d read locks active)", args.Resource, len(lri))
}
if !l.removeEntry(args.Resource, args.UID, &lri) {
return false, fmt.Errorf("Unlock unable to find corresponding lock for uid: %s", args.UID)
}
return true, nil
}
func (l *localLocker) RLock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
lrInfo := lockRequesterInfo{
writer: false,
node: args.ServerAddr,
serviceEndpoint: args.ServiceEndpoint,
uid: args.UID,
timestamp: UTCNow(),
timeLastCheck: UTCNow(),
}
if lri, ok := l.lockMap[args.Resource]; ok {
if reply = !isWriteLock(lri); reply {
// Unless there is a write lock
l.lockMap[args.Resource] = append(l.lockMap[args.Resource], lrInfo)
}
} else {
// No locks held on the given name, so claim (first) read lock
l.lockMap[args.Resource] = []lockRequesterInfo{lrInfo}
reply = true
}
return reply, nil
}
func (l *localLocker) RUnlock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
var lri []lockRequesterInfo
if lri, reply = l.lockMap[args.Resource]; !reply {
// No lock is held on the given name
return reply, fmt.Errorf("RUnlock attempted on an unlocked entity: %s", args.Resource)
}
if reply = !isWriteLock(lri); !reply {
// A write-lock is held, cannot release a read lock
return reply, fmt.Errorf("RUnlock attempted on a write locked entity: %s", args.Resource)
}
if !l.removeEntry(args.Resource, args.UID, &lri) {
return false, fmt.Errorf("RUnlock unable to find corresponding read lock for uid: %s", args.UID)
}
return reply, nil
}
func (l *localLocker) ForceUnlock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
if len(args.UID) != 0 {
return false, fmt.Errorf("ForceUnlock called with non-empty UID: %s", args.UID)
}
if _, ok := l.lockMap[args.Resource]; ok {
// Only clear lock when it is taken
// Remove the lock (irrespective of write or read lock)
delete(l.lockMap, args.Resource)
}
return true, nil
}