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/*
* Minio Cloud Storage, (C) 2016 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 dsync_test
import (
"fmt"
"sync"
. "github.com/minio/dsync"
)
const WriteLock = -1
type lockServer struct {
mutex sync.Mutex
// Map of locks, with negative value indicating (exclusive) write lock
// and positive values indicating number of read locks
lockMap map[string]int64
}
func (l *lockServer) Lock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if _, *reply = l.lockMap[args.Resource]; !*reply {
l.lockMap[args.Resource] = WriteLock // No locks held on the given name, so claim write lock
}
*reply = !*reply // Negate *reply to return true when lock is granted or false otherwise
return nil
}
func (l *lockServer) Unlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
var locksHeld int64
if locksHeld, *reply = l.lockMap[args.Resource]; !*reply { // No lock is held on the given name
return fmt.Errorf("Unlock attempted on an unlocked entity: %s", args.Resource)
}
if *reply = locksHeld == WriteLock; !*reply { // Unless it is a write lock
return fmt.Errorf("Unlock attempted on a read locked entity: %s (%d read locks active)", args.Resource, locksHeld)
}
delete(l.lockMap, args.Resource) // Remove the write lock
return nil
}
const ReadLock = 1
func (l *lockServer) RLock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
var locksHeld int64
if locksHeld, *reply = l.lockMap[args.Resource]; !*reply {
l.lockMap[args.Resource] = ReadLock // No locks held on the given name, so claim (first) read lock
*reply = true
} else {
if *reply = locksHeld != WriteLock; *reply { // Unless there is a write lock
l.lockMap[args.Resource] = locksHeld + ReadLock // Grant another read lock
}
}
return nil
}
func (l *lockServer) RUnlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
var locksHeld int64
if locksHeld, *reply = l.lockMap[args.Resource]; !*reply { // No lock is held on the given name
return fmt.Errorf("RUnlock attempted on an unlocked entity: %s", args.Resource)
}
if *reply = locksHeld != WriteLock; !*reply { // A write-lock is held, cannot release a read lock
return fmt.Errorf("RUnlock attempted on a write locked entity: %s", args.Resource)
}
if locksHeld > ReadLock {
l.lockMap[args.Resource] = locksHeld - ReadLock // Remove one of the read locks held
} else {
delete(l.lockMap, args.Resource) // Remove the (last) read lock
}
return nil
}
func (l *lockServer) ForceUnlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if len(args.UID) != 0 {
return fmt.Errorf("ForceUnlock called with non-empty UID: %s", args.UID)
}
if _, ok := l.lockMap[args.Resource]; ok { // Only clear lock when set
delete(l.lockMap, args.Resource) // Remove the lock (irrespective of write or read lock)
}
*reply = true
return nil
}
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