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minio/cmd/local-locker.go

252 lines
7.2 KiB

/*
* MinIO Cloud Storage, (C) 2018, 2019 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 (
"context"
"fmt"
"sync"
"time"
"github.com/minio/minio/pkg/dsync"
)
// lockRequesterInfo stores various info from the client for each lock that is requested.
type lockRequesterInfo struct {
Writer bool // Bool whether write or read lock.
UID string // UID to uniquely identify request of client.
Timestamp time.Time // Timestamp set at the time of initialization.
TimeLastCheck time.Time // Timestamp for last check of validity of lock.
Source string // Contains line, function and filename reqesting the lock.
// Owner represents the UUID of the owner who originally requested the lock
// useful in expiry.
Owner string
}
// isWriteLock returns whether the lock is a write or read lock.
func isWriteLock(lri []lockRequesterInfo) bool {
return len(lri) == 1 && lri[0].Writer
}
// localLocker implements Dsync.NetLocker
type localLocker struct {
mutex sync.Mutex
endpoint Endpoint
lockMap map[string][]lockRequesterInfo
}
func (l *localLocker) String() string {
return l.endpoint.String()
}
func (l *localLocker) canTakeUnlock(resources ...string) bool {
var lkCnt int
for _, resource := range resources {
isWriteLockTaken := isWriteLock(l.lockMap[resource])
if isWriteLockTaken {
lkCnt++
}
}
return lkCnt == len(resources)
}
func (l *localLocker) canTakeLock(resources ...string) bool {
var noLkCnt int
for _, resource := range resources {
_, lockTaken := l.lockMap[resource]
if !lockTaken {
noLkCnt++
}
}
return noLkCnt == len(resources)
}
func (l *localLocker) Lock(ctx context.Context, args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
if !l.canTakeLock(args.Resources...) {
// Not all locks can be taken on resources,
// reject it completely.
return false, nil
}
// No locks held on the all resources, so claim write
// lock on all resources at once.
for _, resource := range args.Resources {
l.lockMap[resource] = []lockRequesterInfo{
{
Writer: true,
Source: args.Source,
Owner: args.Owner,
UID: args.UID,
Timestamp: UTCNow(),
TimeLastCheck: UTCNow(),
},
}
}
return true, nil
}
func (l *localLocker) Unlock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
if !l.canTakeUnlock(args.Resources...) {
// Unless it is a write lock reject it.
return reply, fmt.Errorf("Unlock attempted on a read locked entity: %s", args.Resources)
}
for _, resource := range args.Resources {
lri := l.lockMap[resource]
if !l.removeEntry(resource, args, &lri) {
return false, fmt.Errorf("Unlock unable to find corresponding lock for uid: %s on resource %s", args.UID, resource)
}
}
return true, nil
}
// removeEntry based on the uid of the lock message, removes a single entry from the
// lockRequesterInfo array or the whole array from the map (in case of a write lock
// or last read lock)
func (l *localLocker) removeEntry(name string, args dsync.LockArgs, lri *[]lockRequesterInfo) bool {
// Find correct entry to remove based on uid.
for index, entry := range *lri {
if entry.UID == args.UID && entry.Owner == args.Owner {
if len(*lri) == 1 {
// Remove the write lock.
delete(l.lockMap, name)
} else {
// Remove the appropriate read lock.
*lri = append((*lri)[:index], (*lri)[index+1:]...)
l.lockMap[name] = *lri
}
return true
}
}
// None found return false, perhaps entry removed in previous run.
return false
}
func (l *localLocker) RLock(ctx context.Context, args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
lrInfo := lockRequesterInfo{
Writer: false,
Source: args.Source,
Owner: args.Owner,
UID: args.UID,
Timestamp: UTCNow(),
TimeLastCheck: UTCNow(),
}
resource := args.Resources[0]
if lri, ok := l.lockMap[resource]; ok {
if reply = !isWriteLock(lri); reply {
// Unless there is a write lock
l.lockMap[resource] = append(l.lockMap[resource], lrInfo)
}
} else {
// No locks held on the given name, so claim (first) read lock
l.lockMap[resource] = []lockRequesterInfo{lrInfo}
reply = true
}
return reply, nil
}
func (l *localLocker) RUnlock(args dsync.LockArgs) (reply bool, err error) {
l.mutex.Lock()
defer l.mutex.Unlock()
var lri []lockRequesterInfo
resource := args.Resources[0]
if lri, reply = l.lockMap[resource]; !reply {
// No lock is held on the given name
return reply, fmt.Errorf("RUnlock attempted on an unlocked entity: %s", resource)
}
if reply = !isWriteLock(lri); !reply {
// A write-lock is held, cannot release a read lock
return reply, fmt.Errorf("RUnlock attempted on a write locked entity: %s", resource)
}
if !l.removeEntry(resource, args, &lri) {
return false, fmt.Errorf("RUnlock unable to find corresponding read lock for uid: %s", args.UID)
}
return reply, nil
}
func (l *localLocker) DupLockMap() map[string][]lockRequesterInfo {
l.mutex.Lock()
defer l.mutex.Unlock()
lockCopy := make(map[string][]lockRequesterInfo)
for k, v := range l.lockMap {
lockCopy[k] = append(lockCopy[k], v...)
}
return lockCopy
}
func (l *localLocker) Close() error {
return nil
}
// Local locker is always online.
func (l *localLocker) IsOnline() bool {
return true
}
func (l *localLocker) Expired(ctx context.Context, args dsync.LockArgs) (expired bool, err error) {
select {
case <-ctx.Done():
return false, ctx.Err()
default:
l.mutex.Lock()
defer l.mutex.Unlock()
// Lock found, proceed to verify if belongs to given uid.
for _, resource := range args.Resources {
if lri, ok := l.lockMap[resource]; ok {
// Check whether uid is still active
for _, entry := range lri {
if entry.UID == args.UID && entry.Owner == args.Owner {
return false, nil
}
}
}
}
return true, nil
}
}
// Similar to removeEntry but only removes an entry only if the lock entry exists in map.
// Caller must hold 'l.mutex' lock.
func (l *localLocker) removeEntryIfExists(nlrip nameLockRequesterInfoPair) {
// Check if entry is still in map (could have been removed altogether by 'concurrent' (R)Unlock of last entry)
if lri, ok := l.lockMap[nlrip.name]; ok {
// Even if the entry exists, it may not be the same entry which was
// considered as expired, so we simply an attempt to remove it if its
// not possible there is nothing we need to do.
l.removeEntry(nlrip.name, dsync.LockArgs{Owner: nlrip.lri.Owner, UID: nlrip.lri.UID}, &lri)
}
}
func newLocker(endpoint Endpoint) *localLocker {
return &localLocker{
endpoint: endpoint,
lockMap: make(map[string][]lockRequesterInfo),
}
}