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minio/namespace-lock.go

126 lines
3.0 KiB

/*
* 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 main
import (
"errors"
"sync"
)
// nsParam - carries name space resource.
type nsParam struct {
volume string
path string
}
// nsLock - provides primitives for locking critical namespace regions.
type nsLock struct {
sync.RWMutex
ref uint
}
// nsLockMap - namespace lock map, provides primitives to Lock,
// Unlock, RLock and RUnlock.
type nsLockMap struct {
lockMap map[nsParam]*nsLock
mutex sync.Mutex
}
// Global name space lock.
var nsMutex *nsLockMap
// initNSLock - initialize name space lock map.
func initNSLock() {
nsMutex = &nsLockMap{
lockMap: make(map[nsParam]*nsLock),
}
}
// Lock the namespace resource.
func (n *nsLockMap) lock(volume, path string, readLock bool) {
n.mutex.Lock()
param := nsParam{volume, path}
nsLk, found := n.lockMap[param]
if !found {
nsLk = &nsLock{
ref: 0,
}
n.lockMap[param] = nsLk
}
nsLk.ref++ // Update ref count here to avoid multiple races.
// Unlock map before Locking NS which might block.
n.mutex.Unlock()
// Locking here can block.
if readLock {
nsLk.RLock()
} else {
nsLk.Lock()
}
}
// Unlock the namespace resource.
func (n *nsLockMap) unlock(volume, path string, readLock bool) {
// nsLk.Unlock() will not block, hence locking the map for the entire function is fine.
n.mutex.Lock()
defer n.mutex.Unlock()
param := nsParam{volume, path}
if nsLk, found := n.lockMap[param]; found {
if readLock {
nsLk.RUnlock()
} else {
nsLk.Unlock()
}
if nsLk.ref == 0 {
errorIf(errors.New("Namespace reference count cannot be 0."), "Invalid reference count detected.")
}
if nsLk.ref != 0 {
nsLk.ref--
}
if nsLk.ref == 0 {
// Remove from the map if there are no more references.
delete(n.lockMap, param)
}
}
}
// Lock - locks the given resource for writes, using a previously
// allocated name space lock or initializing a new one.
func (n *nsLockMap) Lock(volume, path string) {
readLock := false
n.lock(volume, path, readLock)
}
// Unlock - unlocks any previously acquired write locks.
func (n *nsLockMap) Unlock(volume, path string) {
readLock := false
n.unlock(volume, path, readLock)
}
// RLock - locks any previously acquired read locks.
func (n *nsLockMap) RLock(volume, path string) {
readLock := true
n.lock(volume, path, readLock)
}
// RUnlock - unlocks any previously acquired read locks.
func (n *nsLockMap) RUnlock(volume, path string) {
readLock := true
n.unlock(volume, path, readLock)
}