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478 lines
13 KiB
478 lines
13 KiB
/*
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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 dsync
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import (
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"context"
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"errors"
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"math/rand"
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"os"
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"sync"
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"time"
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"github.com/minio/minio/pkg/console"
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)
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// Indicator if logging is enabled.
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var dsyncLog bool
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func init() {
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// Check for MINIO_DSYNC_TRACE env variable, if set logging will be enabled for failed REST operations.
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dsyncLog = os.Getenv("MINIO_DSYNC_TRACE") == "1"
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}
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func log(format string, data ...interface{}) {
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if dsyncLog {
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console.Printf(format, data...)
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}
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}
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// DRWMutexAcquireTimeout - tolerance limit to wait for lock acquisition before.
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const DRWMutexAcquireTimeout = 1 * time.Second // 1 second.
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const drwMutexInfinite = 1<<63 - 1
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// A DRWMutex is a distributed mutual exclusion lock.
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type DRWMutex struct {
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Names []string
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writeLocks []string // Array of nodes that granted a write lock
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readersLocks [][]string // Array of array of nodes that granted reader locks
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m sync.Mutex // Mutex to prevent multiple simultaneous locks from this node
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clnt *Dsync
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}
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// Granted - represents a structure of a granted lock.
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type Granted struct {
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index int
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lockUID string // Locked if set with UID string, unlocked if empty
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}
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func (g *Granted) isLocked() bool {
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return isLocked(g.lockUID)
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}
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func isLocked(uid string) bool {
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return len(uid) > 0
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}
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// NewDRWMutex - initializes a new dsync RW mutex.
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func NewDRWMutex(clnt *Dsync, names ...string) *DRWMutex {
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restClnts, _ := clnt.GetLockers()
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return &DRWMutex{
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writeLocks: make([]string, len(restClnts)),
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Names: names,
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clnt: clnt,
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}
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}
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// Lock holds a write lock on dm.
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//
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// If the lock is already in use, the calling go routine
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// blocks until the mutex is available.
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func (dm *DRWMutex) Lock(id, source string) {
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isReadLock := false
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dm.lockBlocking(context.Background(), id, source, isReadLock, Options{
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Timeout: drwMutexInfinite,
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})
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}
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// Options lock options.
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type Options struct {
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Timeout time.Duration
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}
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// GetLock tries to get a write lock on dm before the timeout elapses.
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//
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// If the lock is already in use, the calling go routine
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// blocks until either the mutex becomes available and return success or
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// more time has passed than the timeout value and return false.
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func (dm *DRWMutex) GetLock(ctx context.Context, id, source string, opts Options) (locked bool) {
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isReadLock := false
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return dm.lockBlocking(ctx, id, source, isReadLock, opts)
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}
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// RLock holds a read lock on dm.
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//
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// If one or more read locks are already in use, it will grant another lock.
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// Otherwise the calling go routine blocks until the mutex is available.
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func (dm *DRWMutex) RLock(id, source string) {
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isReadLock := true
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dm.lockBlocking(context.Background(), id, source, isReadLock, Options{
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Timeout: drwMutexInfinite,
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})
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}
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// GetRLock tries to get a read lock on dm before the timeout elapses.
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//
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// If one or more read locks are already in use, it will grant another lock.
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// Otherwise the calling go routine blocks until either the mutex becomes
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// available and return success or more time has passed than the timeout
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// value and return false.
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func (dm *DRWMutex) GetRLock(ctx context.Context, id, source string, opts Options) (locked bool) {
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isReadLock := true
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return dm.lockBlocking(ctx, id, source, isReadLock, opts)
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}
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const (
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lockRetryInterval = 1 * time.Second
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)
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// lockBlocking will try to acquire either a read or a write lock
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//
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// The function will loop using a built-in timing randomized back-off
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// algorithm until either the lock is acquired successfully or more
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// time has elapsed than the timeout value.
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func (dm *DRWMutex) lockBlocking(ctx context.Context, id, source string, isReadLock bool, opts Options) (locked bool) {
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restClnts, _ := dm.clnt.GetLockers()
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r := rand.New(rand.NewSource(time.Now().UnixNano()))
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// Create lock array to capture the successful lockers
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locks := make([]string, len(restClnts))
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log("lockBlocking %s/%s for %#v: lockType readLock(%t), additional opts: %#v\n", id, source, dm.Names, isReadLock, opts)
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// Add total timeout
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ctx, cancel := context.WithTimeout(ctx, opts.Timeout)
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defer cancel()
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// Tolerance is not set, defaults to half of the locker clients.
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tolerance := len(restClnts) / 2
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// Quorum is effectively = total clients subtracted with tolerance limit
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quorum := len(restClnts) - tolerance
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if !isReadLock {
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// In situations for write locks, as a special case
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// to avoid split brains we make sure to acquire
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// quorum + 1 when tolerance is exactly half of the
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// total locker clients.
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if quorum == tolerance {
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quorum++
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}
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}
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tolerance = len(restClnts) - quorum
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for {
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select {
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case <-ctx.Done():
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return false
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default:
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// Try to acquire the lock.
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if locked = lock(ctx, dm.clnt, &locks, id, source, isReadLock, tolerance, quorum, dm.Names...); locked {
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dm.m.Lock()
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// If success, copy array to object
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if isReadLock {
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// Append new array of strings at the end
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dm.readersLocks = append(dm.readersLocks, make([]string, len(restClnts)))
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// and copy stack array into last spot
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copy(dm.readersLocks[len(dm.readersLocks)-1], locks[:])
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} else {
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copy(dm.writeLocks, locks[:])
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}
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dm.m.Unlock()
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log("lockBlocking %s/%s for %#v: granted\n", id, source, dm.Names)
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return locked
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}
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time.Sleep(time.Duration(r.Float64() * float64(lockRetryInterval)))
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}
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}
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}
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// lock tries to acquire the distributed lock, returning true or false.
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func lock(ctx context.Context, ds *Dsync, locks *[]string, id, source string, isReadLock bool, tolerance, quorum int, lockNames ...string) bool {
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for i := range *locks {
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(*locks)[i] = ""
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}
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restClnts, owner := ds.GetLockers()
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// Create buffered channel of size equal to total number of nodes.
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ch := make(chan Granted, len(restClnts))
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var wg sync.WaitGroup
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// Combined timeout for the lock attempt.
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ctx, cancel := context.WithTimeout(ctx, DRWMutexAcquireTimeout)
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defer cancel()
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for index, c := range restClnts {
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wg.Add(1)
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// broadcast lock request to all nodes
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go func(index int, isReadLock bool, c NetLocker) {
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defer wg.Done()
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g := Granted{index: index}
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if c == nil {
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log("dsync: nil locker\n")
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ch <- g
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return
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}
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args := LockArgs{
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Owner: owner,
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UID: id,
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Resources: lockNames,
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Source: source,
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Quorum: quorum,
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}
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var locked bool
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var err error
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if isReadLock {
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if locked, err = c.RLock(context.Background(), args); err != nil {
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log("dsync: Unable to call RLock failed with %s for %#v at %s\n", err, args, c)
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}
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} else {
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if locked, err = c.Lock(context.Background(), args); err != nil {
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log("dsync: Unable to call Lock failed with %s for %#v at %s\n", err, args, c)
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}
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}
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if locked {
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g.lockUID = args.UID
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}
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ch <- g
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}(index, isReadLock, c)
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}
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// Wait until we have either
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//
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// a) received all lock responses
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// b) received too many 'non-'locks for quorum to be still possible
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// c) timed out
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//
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i, locksFailed := 0, 0
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done := false
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for ; i < len(restClnts); i++ { // Loop until we acquired all locks
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select {
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case grant := <-ch:
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if grant.isLocked() {
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// Mark that this node has acquired the lock
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(*locks)[grant.index] = grant.lockUID
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} else {
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locksFailed++
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if locksFailed > tolerance {
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// We know that we are not going to get the lock anymore,
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// so exit out and release any locks that did get acquired
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done = true
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}
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}
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case <-ctx.Done():
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// Capture timedout locks as failed or took too long
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locksFailed++
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if locksFailed > tolerance {
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// We know that we are not going to get the lock anymore,
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// so exit out and release any locks that did get acquired
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done = true
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}
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}
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if done {
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break
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}
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}
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quorumLocked := checkQuorumLocked(locks, quorum) && locksFailed <= tolerance
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if !quorumLocked {
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log("Releasing all acquired locks now abandoned after quorum was not met\n")
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if !releaseAll(ds, tolerance, owner, locks, isReadLock, restClnts, lockNames...) {
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log("Unable to release acquired locks, stale locks might be present\n")
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}
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}
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// We may have some unused results in ch, release them async.
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go func() {
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wg.Wait()
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close(ch)
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for grantToBeReleased := range ch {
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if grantToBeReleased.isLocked() {
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// release abandoned lock
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log("Releasing abandoned lock\n")
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sendRelease(ds, restClnts[grantToBeReleased.index],
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owner, grantToBeReleased.lockUID, isReadLock, lockNames...)
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}
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}
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}()
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return quorumLocked
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}
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// checkFailedUnlocks determines whether we have sufficiently unlocked all
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// resources to ensure no deadlocks for future callers
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func checkFailedUnlocks(locks []string, tolerance int) bool {
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unlocksFailed := 0
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for lockID := range locks {
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if isLocked(locks[lockID]) {
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unlocksFailed++
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}
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}
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// Unlock failures are higher than tolerance limit
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// for this instance of unlocker, we should let the
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// caller know that lock is not successfully released
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// yet.
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if len(locks)-tolerance == tolerance {
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// Incase of split brain scenarios where
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// tolerance is exactly half of the len(*locks)
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// then we need to make sure we have unlocked
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// upto tolerance+1 - especially for RUnlock
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// to ensure that we don't end up with active
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// read locks on the resource after unlocking
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// only half of the lockers.
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return unlocksFailed >= tolerance
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}
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return unlocksFailed > tolerance
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}
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// checkQuorumLocked determines whether we have locked the required quorum of underlying locks or not
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func checkQuorumLocked(locks *[]string, quorum int) bool {
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count := 0
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for _, uid := range *locks {
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if isLocked(uid) {
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count++
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}
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}
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return count >= quorum
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}
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// releaseAll releases all locks that are marked as locked
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func releaseAll(ds *Dsync, tolerance int, owner string, locks *[]string, isReadLock bool, restClnts []NetLocker, lockNames ...string) bool {
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var wg sync.WaitGroup
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for lockID := range restClnts {
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wg.Add(1)
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go func(lockID int) {
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defer wg.Done()
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if isLocked((*locks)[lockID]) {
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if sendRelease(ds, restClnts[lockID], owner, (*locks)[lockID], isReadLock, lockNames...) {
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(*locks)[lockID] = ""
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}
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}
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}(lockID)
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}
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wg.Wait()
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// Return true if releaseAll was successful, otherwise we return 'false'
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// to indicate we haven't sufficiently unlocked lockers to avoid deadlocks.
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//
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// Caller may use this as an indication to call again.
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return !checkFailedUnlocks(*locks, tolerance)
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}
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// Unlock unlocks the write lock.
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//
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// It is a run-time error if dm is not locked on entry to Unlock.
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func (dm *DRWMutex) Unlock() {
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restClnts, owner := dm.clnt.GetLockers()
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// create temp array on stack
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locks := make([]string, len(restClnts))
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{
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dm.m.Lock()
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defer dm.m.Unlock()
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// Check if minimally a single bool is set in the writeLocks array
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lockFound := false
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for _, uid := range dm.writeLocks {
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if isLocked(uid) {
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lockFound = true
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break
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}
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}
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if !lockFound {
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panic("Trying to Unlock() while no Lock() is active")
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}
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// Copy write locks to stack array
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copy(locks, dm.writeLocks[:])
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}
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// Tolerance is not set, defaults to half of the locker clients.
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tolerance := len(restClnts) / 2
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isReadLock := false
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r := rand.New(rand.NewSource(time.Now().UnixNano()))
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for !releaseAll(dm.clnt, tolerance, owner, &locks, isReadLock, restClnts, dm.Names...) {
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time.Sleep(time.Duration(r.Float64() * float64(lockRetryInterval)))
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}
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}
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// RUnlock releases a read lock held on dm.
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//
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// It is a run-time error if dm is not locked on entry to RUnlock.
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func (dm *DRWMutex) RUnlock() {
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// create temp array on stack
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restClnts, owner := dm.clnt.GetLockers()
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locks := make([]string, len(restClnts))
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{
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dm.m.Lock()
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defer dm.m.Unlock()
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if len(dm.readersLocks) == 0 {
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panic("Trying to RUnlock() while no RLock() is active")
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}
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// Copy out first element to release it first (FIFO)
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copy(locks, dm.readersLocks[0][:])
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// Drop first element from array
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dm.readersLocks = dm.readersLocks[1:]
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}
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// Tolerance is not set, defaults to half of the locker clients.
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tolerance := len(restClnts) / 2
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isReadLock := true
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r := rand.New(rand.NewSource(time.Now().UnixNano()))
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for !releaseAll(dm.clnt, tolerance, owner, &locks, isReadLock, restClnts, dm.Names...) {
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time.Sleep(time.Duration(r.Float64() * float64(lockRetryInterval)))
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}
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}
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// sendRelease sends a release message to a node that previously granted a lock
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func sendRelease(ds *Dsync, c NetLocker, owner string, uid string, isReadLock bool, names ...string) bool {
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if c == nil {
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log("Unable to call RUnlock failed with %s\n", errors.New("netLocker is offline"))
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return false
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}
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args := LockArgs{
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Owner: owner,
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UID: uid,
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Resources: names,
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}
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if isReadLock {
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if _, err := c.RUnlock(args); err != nil {
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log("dsync: Unable to call RUnlock failed with %s for %#v at %s\n", err, args, c)
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return false
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}
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} else {
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if _, err := c.Unlock(args); err != nil {
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log("dsync: Unable to call Unlock failed with %s for %#v at %s\n", err, args, c)
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return false
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}
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}
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return true
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}
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