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