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minio/cmd/local-locker.go

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/*
* MinIO Cloud Storage, (C) 2018, 2019 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 (
"errors"
"fmt"
"sync"
"time"
"github.com/minio/minio/pkg/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.
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.
Source string // Contains line, function and filename reqesting the lock.
}
// isWriteLock returns whether the lock is a write or read lock.
func isWriteLock(lri []lockRequesterInfo) bool {
return len(lri) == 1 && lri[0].Writer
}
type errorLocker struct{}
func (d *errorLocker) String() string {
return ""
}
func (d *errorLocker) Lock(args dsync.LockArgs) (reply bool, err error) {
return false, errors.New("unable to lock")
}
func (d *errorLocker) Unlock(args dsync.LockArgs) (reply bool, err error) {
return false, errors.New("unable to unlock")
}
func (d *errorLocker) RLock(args dsync.LockArgs) (reply bool, err error) {
return false, errors.New("unable to rlock")
}
func (d *errorLocker) RUnlock(args dsync.LockArgs) (reply bool, err error) {
return false, errors.New("unable to runlock")
}
func (d *errorLocker) Close() error {
return nil
}
func (d *errorLocker) IsOnline() bool {
return false
}
// localLocker implements Dsync.NetLocker
type localLocker struct {
mutex sync.Mutex
endpoint Endpoint
lockMap map[string][]lockRequesterInfo
}
func (l *localLocker) String() string {
return l.endpoint.String()
}
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,
Source: args.Source,
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
}
// removeEntry based on the uid of the lock message, removes a single entry from the
// lockRequesterInfo array or the whole array from the map (in case of a write lock
// or last read lock)
func (l *localLocker) removeEntry(name, uid string, lri *[]lockRequesterInfo) bool {
// Find correct entry to remove based on uid.
for index, entry := range *lri {
if entry.UID == uid {
if len(*lri) == 1 {
// Remove the write lock.
delete(l.lockMap, name)
} else {
// Remove the appropriate read lock.
*lri = append((*lri)[:index], (*lri)[index+1:]...)
l.lockMap[name] = *lri
}
return true
}
}
// None found return false, perhaps entry removed in previous run.
return false
}
func (l *localLocker) RLock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
lrInfo := lockRequesterInfo{
Writer: false,
Source: args.Source,
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) DupLockMap() map[string][]lockRequesterInfo {
l.mutex.Lock()
defer l.mutex.Unlock()
lockCopy := make(map[string][]lockRequesterInfo)
for k, v := range l.lockMap {
lockCopy[k] = append(lockCopy[k], v...)
}
return lockCopy
}
func (l *localLocker) Close() error {
return nil
}
// Local locker is always online.
func (l *localLocker) IsOnline() bool {
return true
}
func newLocker(endpoint Endpoint) *localLocker {
return &localLocker{
endpoint: endpoint,
lockMap: make(map[string][]lockRequesterInfo),
}
}