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minio/cmd/lock-rpc-server.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 (
"fmt"
"math/rand"
"net/rpc"
"path"
"sync"
"time"
router "github.com/gorilla/mux"
"github.com/minio/dsync"
)
const (
// Lock rpc server endpoint.
lockRPCPath = "/minio/lock"
// Lock maintenance interval.
lockMaintenanceInterval = 1 * time.Minute // 1 minute.
// Lock validity check interval.
lockValidityCheckInterval = 2 * time.Minute // 2 minutes.
)
// lockRequesterInfo stores various info from the client for each lock that is requested
type lockRequesterInfo struct {
writer bool // Bool whether write or read lock
node string // Network address of client claiming lock
rpcPath string // RPC path of client claiming 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
}
// isWriteLock returns whether the lock is a write or read lock
func isWriteLock(lri []lockRequesterInfo) bool {
return len(lri) == 1 && lri[0].writer
}
// lockServer is type for RPC handlers
type lockServer struct {
AuthRPCServer
rpcPath string
mutex sync.Mutex
lockMap map[string][]lockRequesterInfo
}
// Start lock maintenance from all lock servers.
func startLockMaintainence(lockServers []*lockServer) {
for _, locker := range lockServers {
// Start loop for stale lock maintenance
go func(lk *lockServer) {
// Initialize a new ticker with a minute between each ticks.
ticker := time.NewTicker(lockMaintenanceInterval)
// Start with random sleep time, so as to avoid "synchronous checks" between servers
time.Sleep(time.Duration(rand.Float64() * float64(lockMaintenanceInterval)))
for {
// Verifies every minute for locks held more than 2minutes.
select {
case <-ticker.C:
lk.lockMaintenance(lockValidityCheckInterval)
case <-globalServiceDoneCh:
// Stop the timer.
ticker.Stop()
}
}
}(locker)
}
}
// Register distributed NS lock handlers.
func registerDistNSLockRouter(mux *router.Router, serverConfig serverCmdConfig) error {
// Initialize a new set of lock servers.
lockServers := newLockServers(serverConfig)
// Start lock maintenance from all lock servers.
startLockMaintainence(lockServers)
// Register initialized lock servers to their respective rpc endpoints.
return registerStorageLockers(mux, lockServers)
}
// Create one lock server for every local storage rpc server.
func newLockServers(srvConfig serverCmdConfig) (lockServers []*lockServer) {
for _, ep := range srvConfig.endpoints {
// Initialize new lock server for each local node.
if isLocalStorage(ep) {
// Create handler for lock RPCs
locker := &lockServer{
rpcPath: getPath(ep),
mutex: sync.Mutex{},
lockMap: make(map[string][]lockRequesterInfo),
}
lockServers = append(lockServers, locker)
}
}
return lockServers
}
// registerStorageLockers - register locker rpc handlers for net/rpc library clients
func registerStorageLockers(mux *router.Router, lockServers []*lockServer) error {
for _, lockServer := range lockServers {
lockRPCServer := rpc.NewServer()
if err := lockRPCServer.RegisterName("Dsync", lockServer); err != nil {
return traceError(err)
}
lockRouter := mux.PathPrefix(reservedBucket).Subrouter()
lockRouter.Path(path.Join("/lock", lockServer.rpcPath)).Handler(lockRPCServer)
}
return nil
}
/// Distributed lock handlers
// Lock - rpc handler for (single) write lock operation.
func (l *lockServer) Lock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
_, *reply = l.lockMap[args.LockArgs.Resource]
if !*reply { // No locks held on the given name, so claim write lock
l.lockMap[args.LockArgs.Resource] = []lockRequesterInfo{
{
writer: true,
node: args.LockArgs.ServerAddr,
rpcPath: args.LockArgs.ServiceEndpoint,
uid: args.LockArgs.UID,
timestamp: time.Now().UTC(),
timeLastCheck: time.Now().UTC(),
},
}
}
*reply = !*reply // Negate *reply to return true when lock is granted or false otherwise
return nil
}
// Unlock - rpc handler for (single) write unlock operation.
func (l *lockServer) Unlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
var lri []lockRequesterInfo
if lri, *reply = l.lockMap[args.LockArgs.Resource]; !*reply { // No lock is held on the given name
return fmt.Errorf("Unlock attempted on an unlocked entity: %s", args.LockArgs.Resource)
}
if *reply = isWriteLock(lri); !*reply { // Unless it is a write lock
return fmt.Errorf("Unlock attempted on a read locked entity: %s (%d read locks active)", args.LockArgs.Resource, len(lri))
}
if !l.removeEntry(args.LockArgs.Resource, args.LockArgs.UID, &lri) {
return fmt.Errorf("Unlock unable to find corresponding lock for uid: %s", args.LockArgs.UID)
}
return nil
}
// RLock - rpc handler for read lock operation.
func (l *lockServer) RLock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
lrInfo := lockRequesterInfo{
writer: false,
node: args.LockArgs.ServerAddr,
rpcPath: args.LockArgs.ServiceEndpoint,
uid: args.LockArgs.UID,
timestamp: time.Now().UTC(),
timeLastCheck: time.Now().UTC(),
}
if lri, ok := l.lockMap[args.LockArgs.Resource]; ok {
if *reply = !isWriteLock(lri); *reply { // Unless there is a write lock
l.lockMap[args.LockArgs.Resource] = append(l.lockMap[args.LockArgs.Resource], lrInfo)
}
} else { // No locks held on the given name, so claim (first) read lock
l.lockMap[args.LockArgs.Resource] = []lockRequesterInfo{lrInfo}
*reply = true
}
return nil
}
// RUnlock - rpc handler for read unlock operation.
func (l *lockServer) RUnlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
var lri []lockRequesterInfo
if lri, *reply = l.lockMap[args.LockArgs.Resource]; !*reply { // No lock is held on the given name
return fmt.Errorf("RUnlock attempted on an unlocked entity: %s", args.LockArgs.Resource)
}
if *reply = !isWriteLock(lri); !*reply { // A write-lock is held, cannot release a read lock
return fmt.Errorf("RUnlock attempted on a write locked entity: %s", args.LockArgs.Resource)
}
if !l.removeEntry(args.LockArgs.Resource, args.LockArgs.UID, &lri) {
return fmt.Errorf("RUnlock unable to find corresponding read lock for uid: %s", args.LockArgs.UID)
}
return nil
}
// ForceUnlock - rpc handler for force unlock operation.
func (l *lockServer) ForceUnlock(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
if len(args.LockArgs.UID) != 0 {
return fmt.Errorf("ForceUnlock called with non-empty UID: %s", args.LockArgs.UID)
}
if _, ok := l.lockMap[args.LockArgs.Resource]; ok { // Only clear lock when set
delete(l.lockMap, args.LockArgs.Resource) // Remove the lock (irrespective of write or read lock)
}
*reply = true
return nil
}
// Expired - rpc handler for expired lock status.
func (l *lockServer) Expired(args *LockArgs, reply *bool) error {
l.mutex.Lock()
defer l.mutex.Unlock()
if err := args.IsAuthenticated(); err != nil {
return err
}
// Lock found, proceed to verify if belongs to given uid.
if lri, ok := l.lockMap[args.LockArgs.Resource]; ok {
// Check whether uid is still active
for _, entry := range lri {
if entry.uid == args.LockArgs.UID {
*reply = false // When uid found, lock is still active so return not expired.
return nil // When uid found *reply is set to true.
}
}
}
// When we get here lock is no longer active due to either args.LockArgs.Resource
// being absent from map or uid not found for given args.LockArgs.Resource
*reply = true
return nil
}
// nameLockRequesterInfoPair is a helper type for lock maintenance
type nameLockRequesterInfoPair struct {
name string
lri lockRequesterInfo
}
// lockMaintenance loops over locks that have been active for some time and checks back
// with the original server whether it is still alive or not
//
// Following logic inside ignores the errors generated for Dsync.Active operation.
// - server at client down
// - some network error (and server is up normally)
//
// We will ignore the error, and we will retry later to get a resolve on this lock
func (l *lockServer) lockMaintenance(interval time.Duration) {
l.mutex.Lock()
// Get list of long lived locks to check for staleness.
nlripLongLived := getLongLivedLocks(l.lockMap, interval)
l.mutex.Unlock()
serverCred := serverConfig.GetCredential()
// Validate if long lived locks are indeed clean.
for _, nlrip := range nlripLongLived {
// Initialize client based on the long live locks.
c := newLockRPCClient(authConfig{
accessKey: serverCred.AccessKey,
secretKey: serverCred.SecretKey,
serverAddr: nlrip.lri.node,
serviceEndpoint: nlrip.lri.rpcPath,
secureConn: isSSL(),
serviceName: "Dsync",
})
// Call back to original server verify whether the lock is still active (based on name & uid)
expired, _ := c.Expired(dsync.LockArgs{UID: nlrip.lri.uid, Resource: nlrip.name})
// Close the connection regardless of the call response.
c.rpcClient.Close()
// For successful response, verify if lock is indeed active or stale.
if expired {
// The lock is no longer active at server that originated the lock
// So remove the lock from the map.
l.mutex.Lock()
l.removeEntryIfExists(nlrip) // Purge the stale entry if it exists.
l.mutex.Unlock()
}
}
}