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121 lines
3.9 KiB
Go
121 lines
3.9 KiB
Go
// Copyright (c) 2015-2021 MinIO, Inc.
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//
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// This file is part of MinIO Object Storage stack
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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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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// Refresh returns lock not found if set to true
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lockNotFound bool
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}
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func (l *lockServer) setRefreshReply(refreshed bool) {
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l.mutex.Lock()
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defer l.mutex.Unlock()
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l.lockNotFound = !refreshed
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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) Refresh(args *LockArgs, reply *bool) error {
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l.mutex.Lock()
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defer l.mutex.Unlock()
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*reply = !l.lockNotFound
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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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