minio/cmd/namespace-lock.go

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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 cmd
import (
"errors"
pathutil "path"
"strconv"
"strings"
"sync"
"github.com/minio/dsync"
)
// Global name space lock.
var nsMutex *nsLockMap
// Initialize distributed locking only in case of distributed setup.
// Returns if the setup is distributed or not on success.
func initDsyncNodes(disks []string, port int) error {
serverPort := strconv.Itoa(port)
cred := serverConfig.GetCredential()
// Initialize rpc lock client information only if this instance is a distributed setup.
var clnts []dsync.RPC
for _, disk := range disks {
if idx := strings.LastIndex(disk, ":"); idx != -1 {
clnts = append(clnts, newAuthClient(&authConfig{
accessKey: cred.AccessKeyID,
secretKey: cred.SecretAccessKey,
// Construct a new dsync server addr.
address: disk[:idx] + ":" + serverPort,
// Construct a new rpc path for the disk.
path: pathutil.Join(lockRPCPath, disk[idx+1:]),
loginMethod: "Dsync.LoginHandler",
}))
}
}
return dsync.SetNodesWithClients(clnts)
}
// initNSLock - initialize name space lock map.
func initNSLock(isDist bool) {
nsMutex = &nsLockMap{
isDist: isDist,
lockMap: make(map[nsParam]*nsLock),
}
}
// RWLocker - interface that any read-write locking library should implement.
type RWLocker interface {
sync.Locker
RLock()
RUnlock()
}
// nsParam - carries name space resource.
type nsParam struct {
volume string
path string
}
// nsLock - provides primitives for locking critical namespace regions.
type nsLock struct {
writer RWLocker
readerArray []RWLocker
ref uint
}
// nsLockMap - namespace lock map, provides primitives to Lock,
// Unlock, RLock and RUnlock.
type nsLockMap struct {
isDist bool // indicates whether the locking service is part of a distributed setup or not.
lockMap map[nsParam]*nsLock
lockMapMutex sync.Mutex
}
// Lock the namespace resource.
func (n *nsLockMap) lock(volume, path string, readLock bool) {
var nsLk *nsLock
n.lockMapMutex.Lock()
param := nsParam{volume, path}
nsLk, found := n.lockMap[param]
if !found {
nsLk = &nsLock{
writer: func() RWLocker {
if n.isDist {
return dsync.NewDRWMutex(pathutil.Join(volume, path))
}
return &sync.RWMutex{}
}(),
ref: 0,
}
n.lockMap[param] = nsLk
}
nsLk.ref++ // Update ref count here to avoid multiple races.
rwlock := nsLk.writer
if readLock && n.isDist {
rwlock = dsync.NewDRWMutex(pathutil.Join(volume, path))
}
// Unlock map before Locking NS which might block.
n.lockMapMutex.Unlock()
// Locking here can block.
if readLock {
rwlock.RLock()
if n.isDist {
// Only add (for reader case) to array after RLock() succeeds
// (so that we know for sure that element in [0] can be RUnlocked())
n.lockMapMutex.Lock()
if len(nsLk.readerArray) == 0 {
nsLk.readerArray = []RWLocker{rwlock}
} else {
nsLk.readerArray = append(nsLk.readerArray, rwlock)
}
n.lockMapMutex.Unlock()
}
} else {
rwlock.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.lockMapMutex.Lock()
defer n.lockMapMutex.Unlock()
param := nsParam{volume, path}
if nsLk, found := n.lockMap[param]; found {
if readLock {
if n.isDist {
if len(nsLk.readerArray) == 0 {
errorIf(errors.New("Length of reader lock array cannot be 0."), "Invalid reader lock array length detected.")
}
// Release first lock first (FIFO)
nsLk.readerArray[0].RUnlock()
// And discard first element
nsLk.readerArray = nsLk.readerArray[1:]
} else {
nsLk.writer.RUnlock()
}
} else {
nsLk.writer.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 {
if len(nsLk.readerArray) != 0 && n.isDist {
errorIf(errors.New("Length of reader lock array should be 0 upon deleting map entry."), "Invalid reader lock array length detected.")
}
// 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)
}