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