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"
"net/url"
pathutil "path"
"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(eps []*url.URL) error {
cred := serverConfig.GetCredential()
// Initialize rpc lock client information only if this instance is a distributed setup.
var clnts []dsync.RPC
myNode := -1
for _, ep := range eps {
if ep == nil {
return errInvalidArgument
}
clnts = append(clnts, newAuthClient(&authConfig{
accessKey: cred.AccessKeyID,
secretKey: cred.SecretAccessKey,
// Construct a new dsync server addr.
secureConn: isSSL(),
address: ep.Host,
// Construct a new rpc path for the endpoint.
path: pathutil.Join(lockRPCPath, getPath(ep)),
loginMethod: "Dsync.LoginHandler",
}))
if isLocalStorage(ep) && myNode == -1 {
myNode = len(clnts) - 1
}
}
return dsync.SetNodesWithClients(clnts, myNode)
}
// initNSLock - initialize name space lock map.
func initNSLock(isDist bool) {
nsMutex = &nsLockMap{
isDist: isDist,
lockMap: make(map[nsParam]*nsLock),
}
// Initialize nsLockMap with entry for instrumentation information.
// Entries of <volume,path> -> stateInfo of locks
nsMutex.debugLockMap = make(map[nsParam]*debugLockInfoPerVolumePath)
}
// 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 {
RWLocker
ref uint
}
// nsLockMap - namespace lock map, provides primitives to Lock,
// Unlock, RLock and RUnlock.
type nsLockMap struct {
// Lock counter used for lock debugging.
globalLockCounter int64 // Total locks held.
blockedCounter int64 // Total operations blocked waiting for locks.
runningLockCounter int64 // Total locks held but not released yet.
debugLockMap map[nsParam]*debugLockInfoPerVolumePath // Info for instrumentation on locks.
// Indicates whether the locking service is part
// of a distributed setup or not.
isDist bool
lockMap map[nsParam]*nsLock
lockMapMutex sync.Mutex
}
// Lock the namespace resource.
func (n *nsLockMap) lock(volume, path string, lockOrigin, opsID string, readLock bool) {
var nsLk *nsLock
n.lockMapMutex.Lock()
param := nsParam{volume, path}
nsLk, found := n.lockMap[param]
if !found {
nsLk = &nsLock{
RWLocker: 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.
// Change the state of the lock to be blocked for the given
// pair of <volume, path> and <OperationID> till the lock
// unblocks. The lock for accessing `nsMutex` is held inside
// the function itself.
if err := n.statusNoneToBlocked(param, lockOrigin, opsID, readLock); err != nil {
errorIf(err, "Failed to set lock state to blocked.")
}
// Unlock map before Locking NS which might block.
n.lockMapMutex.Unlock()
// Locking here can block.
if readLock {
nsLk.RLock()
} else {
nsLk.Lock()
}
// Changing the status of the operation from blocked to
// running. change the state of the lock to be running (from
// blocked) for the given pair of <volume, path> and <OperationID>.
if err := n.statusBlockedToRunning(param, lockOrigin, opsID, readLock); err != nil {
errorIf(err, "Failed to set the lock state to running.")
}
}
// Unlock the namespace resource.
func (n *nsLockMap) unlock(volume, path, opsID 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 {
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--
// delete the lock state entry for given operation ID.
err := n.deleteLockInfoEntryForOps(param, opsID)
if err != nil {
errorIf(err, "Failed to delete lock info entry.")
}
}
if nsLk.ref == 0 {
// Remove from the map if there are no more references.
delete(n.lockMap, param)
// delete the lock state entry for given
// <volume, path> pair.
err := n.deleteLockInfoEntryForVolumePath(param)
if err != nil {
errorIf(err, "Failed to delete lock info entry.")
}
}
}
}
// 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, opsID string) {
readLock := false // This is a write lock.
lockLocation := callerLocation() // Useful for debugging
n.lock(volume, path, lockLocation, opsID, readLock)
}
// Unlock - unlocks any previously acquired write locks.
func (n *nsLockMap) Unlock(volume, path, opsID string) {
readLock := false
n.unlock(volume, path, opsID, readLock)
}
// RLock - locks any previously acquired read locks.
func (n *nsLockMap) RLock(volume, path, opsID string) {
readLock := true
lockLocation := callerLocation() // Useful for debugging
n.lock(volume, path, lockLocation, opsID, readLock)
}
// RUnlock - unlocks any previously acquired read locks.
func (n *nsLockMap) RUnlock(volume, path, opsID string) {
readLock := true
n.unlock(volume, path, opsID, readLock)
}
// ForceUnlock - forcefully unlock a lock based on name.
func (n *nsLockMap) ForceUnlock(volume, path string) {
n.lockMapMutex.Lock()
defer n.lockMapMutex.Unlock()
// Clarification on operation:
// - In case of FS or XL we call ForceUnlock on the local nsMutex
// (since there is only a single server) which will cause the 'stuck'
// mutex to be removed from the map. Existing operations for this
// will continue to be blocked (and timeout). New operations on this
// resource will use a new mutex and proceed normally.
//
// - In case of Distributed setup (using dsync), there is no need to call
// ForceUnlock on the server where the lock was acquired and is presumably
// 'stuck'. Instead dsync.ForceUnlock() will release the underlying locks
// that participated in granting the lock. Any pending dsync locks that
// are blocking can now proceed as normal and any new locks will also
// participate normally.
if n.isDist { // For distributed mode, broadcast ForceUnlock message.
dsync.NewDRWMutex(pathutil.Join(volume, path)).ForceUnlock()
}
param := nsParam{volume, path}
if _, found := n.lockMap[param]; found {
// Remove lock from the map.
delete(n.lockMap, param)
// delete the lock state entry for given
// <volume, path> pair.
err := n.deleteLockInfoEntryForVolumePath(param)
if err != nil {
errorIf(err, "Failed to delete lock info entry.")
}
}
}