/usr/share/gocode/src/github.com/minio/dsync/drwmutex.go is in golang-github-minio-dsync-dev 0.0~git20170209.0.b9f7da7-1.
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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 dsync
import (
cryptorand "crypto/rand"
"fmt"
golog "log"
"math"
"math/rand"
"net"
"os"
"sync"
"time"
)
// Indicator if logging is enabled.
var dsyncLog bool
func init() {
// Check for DSYNC_LOG env variable, if set logging will be enabled for failed RPC operations.
dsyncLog = os.Getenv("DSYNC_LOG") == "1"
}
func log(msg ...interface{}) {
if dsyncLog {
golog.Println(msg...)
}
}
// DRWMutexAcquireTimeout - tolerance limit to wait for lock acquisition before.
const DRWMutexAcquireTimeout = 25 * time.Millisecond // 25ms.
// A DRWMutex is a distributed mutual exclusion lock.
type DRWMutex struct {
Name string
writeLocks []string // Array of nodes that granted a write lock
readersLocks [][]string // Array of array of nodes that granted reader locks
m sync.Mutex // Mutex to prevent multiple simultaneous locks from this node
}
type Granted struct {
index int
lockUid string // Locked if set with UID string, unlocked if empty
}
func (g *Granted) isLocked() bool {
return isLocked(g.lockUid)
}
func isLocked(uid string) bool {
return len(uid) > 0
}
func NewDRWMutex(name string) *DRWMutex {
return &DRWMutex{
Name: name,
writeLocks: make([]string, dnodeCount),
}
}
// Lock holds a write lock on dm.
//
// If the lock is already in use, the calling go routine
// blocks until the mutex is available.
func (dm *DRWMutex) Lock() {
isReadLock := false
dm.lockBlocking(isReadLock)
}
// RLock holds a read lock on dm.
//
// If one or more read lock are already in use, it will grant another lock.
// Otherwise the calling go routine blocks until the mutex is available.
func (dm *DRWMutex) RLock() {
isReadLock := true
dm.lockBlocking(isReadLock)
}
// lockBlocking will acquire either a read or a write lock
//
// The call will block until the lock is granted using a built-in
// timing randomized back-off algorithm to try again until successful
func (dm *DRWMutex) lockBlocking(isReadLock bool) {
runs, backOff := 1, 1
for {
// create temp array on stack
locks := make([]string, dnodeCount)
// try to acquire the lock
success := lock(clnts, &locks, dm.Name, isReadLock)
if success {
dm.m.Lock()
defer dm.m.Unlock()
// if success, copy array to object
if isReadLock {
// append new array of strings at the end
dm.readersLocks = append(dm.readersLocks, make([]string, dnodeCount))
// and copy stack array into last spot
copy(dm.readersLocks[len(dm.readersLocks)-1], locks[:])
} else {
copy(dm.writeLocks, locks[:])
}
return
}
// We timed out on the previous lock, incrementally wait for a longer back-off time,
// and try again afterwards
time.Sleep(time.Duration(backOff) * time.Millisecond)
backOff += int(rand.Float64() * math.Pow(2, float64(runs)))
if backOff > 1024 {
backOff = backOff % 64
runs = 1 // reset runs
} else if runs < 10 {
runs++
}
}
}
// lock tries to acquire the distributed lock, returning true or false
//
func lock(clnts []NetLocker, locks *[]string, lockName string, isReadLock bool) bool {
// Create buffered channel of size equal to total number of nodes.
ch := make(chan Granted, dnodeCount)
for index, c := range clnts {
// broadcast lock request to all nodes
go func(index int, isReadLock bool, c NetLocker) {
// All client methods issuing RPCs are thread-safe and goroutine-safe,
// i.e. it is safe to call them from multiple concurrently running go routines.
bytesUid := [16]byte{}
cryptorand.Read(bytesUid[:])
uid := fmt.Sprintf("%X", bytesUid[:])
args := LockArgs{
UID: uid,
Resource: lockName,
ServerAddr: clnts[ownNode].ServerAddr(),
ServiceEndpoint: clnts[ownNode].ServiceEndpoint(),
}
var locked bool
var err error
if isReadLock {
if locked, err = c.RLock(args); err != nil {
log("Unable to call RLock", err)
}
} else {
if locked, err = c.Lock(args); err != nil {
log("Unable to call Lock", err)
}
}
g := Granted{index: index}
if locked {
g.lockUid = args.UID
}
ch <- g
}(index, isReadLock, c)
}
quorum := false
var wg sync.WaitGroup
wg.Add(1)
go func(isReadLock bool) {
// Wait until we have either a) received all lock responses, b) received too many 'non-'locks for quorum to be or c) time out
i, locksFailed := 0, 0
done := false
timeout := time.After(DRWMutexAcquireTimeout)
for ; i < dnodeCount; i++ { // Loop until we acquired all locks
select {
case grant := <-ch:
if grant.isLocked() {
// Mark that this node has acquired the lock
(*locks)[grant.index] = grant.lockUid
} else {
locksFailed++
if !isReadLock && locksFailed > dnodeCount-dquorum ||
isReadLock && locksFailed > dnodeCount-dquorumReads {
// We know that we are not going to get the lock anymore, so exit out
// and release any locks that did get acquired
done = true
// Increment the number of grants received from the buffered channel.
i++
releaseAll(clnts, locks, lockName, isReadLock)
}
}
case <-timeout:
done = true
// timeout happened, maybe one of the nodes is slow, count
// number of locks to check whether we have quorum or not
if !quorumMet(locks, isReadLock) {
releaseAll(clnts, locks, lockName, isReadLock)
}
}
if done {
break
}
}
// Count locks in order to determine whterh we have quorum or not
quorum = quorumMet(locks, isReadLock)
// Signal that we have the quorum
wg.Done()
// Wait for the other responses and immediately release the locks
// (do not add them to the locks array because the DRWMutex could
// already has been unlocked again by the original calling thread)
for ; i < dnodeCount; i++ {
grantToBeReleased := <-ch
if grantToBeReleased.isLocked() {
// release lock
sendRelease(clnts[grantToBeReleased.index], lockName, grantToBeReleased.lockUid, isReadLock)
}
}
}(isReadLock)
wg.Wait()
// Verify that localhost server is actively participating in the lock (the lock maintenance relies on this fact)
if quorum && !isLocked((*locks)[ownNode]) {
// If not, release lock (and try again later)
releaseAll(clnts, locks, lockName, isReadLock)
quorum = false
}
return quorum
}
// quorumMet determines whether we have acquired the required quorum of underlying locks or not
func quorumMet(locks *[]string, isReadLock bool) bool {
count := 0
for _, uid := range *locks {
if isLocked(uid) {
count++
}
}
if isReadLock {
return count >= dquorumReads
} else {
return count >= dquorum
}
}
// releaseAll releases all locks that are marked as locked
func releaseAll(clnts []NetLocker, locks *[]string, lockName string, isReadLock bool) {
for lock := 0; lock < dnodeCount; lock++ {
if isLocked((*locks)[lock]) {
sendRelease(clnts[lock], lockName, (*locks)[lock], isReadLock)
(*locks)[lock] = ""
}
}
}
// Unlock unlocks the write lock.
//
// It is a run-time error if dm is not locked on entry to Unlock.
func (dm *DRWMutex) Unlock() {
// create temp array on stack
locks := make([]string, dnodeCount)
{
dm.m.Lock()
defer dm.m.Unlock()
// Check if minimally a single bool is set in the writeLocks array
lockFound := false
for _, uid := range dm.writeLocks {
if isLocked(uid) {
lockFound = true
break
}
}
if !lockFound {
panic("Trying to Unlock() while no Lock() is active")
}
// Copy write locks to stack array
copy(locks, dm.writeLocks[:])
// Clear write locks array
dm.writeLocks = make([]string, dnodeCount)
}
isReadLock := false
unlock(locks, dm.Name, isReadLock)
}
// RUnlock releases a read lock held on dm.
//
// It is a run-time error if dm is not locked on entry to RUnlock.
func (dm *DRWMutex) RUnlock() {
// create temp array on stack
locks := make([]string, dnodeCount)
{
dm.m.Lock()
defer dm.m.Unlock()
if len(dm.readersLocks) == 0 {
panic("Trying to RUnlock() while no RLock() is active")
}
// Copy out first element to release it first (FIFO)
copy(locks, dm.readersLocks[0][:])
// Drop first element from array
dm.readersLocks = dm.readersLocks[1:]
}
isReadLock := true
unlock(locks, dm.Name, isReadLock)
}
func unlock(locks []string, name string, isReadLock bool) {
// We don't need to synchronously wait until we have released all the locks (or the quorum)
// (a subsequent lock will retry automatically in case it would fail to get quorum)
for index, c := range clnts {
if isLocked(locks[index]) {
// broadcast lock release to all nodes that granted the lock
sendRelease(c, name, locks[index], isReadLock)
}
}
}
// ForceUnlock will forcefully clear a write or read lock.
func (dm *DRWMutex) ForceUnlock() {
{
dm.m.Lock()
defer dm.m.Unlock()
// Clear write locks array
dm.writeLocks = make([]string, dnodeCount)
// Clear read locks array
dm.readersLocks = nil
}
for _, c := range clnts {
// broadcast lock release to all nodes that granted the lock
sendRelease(c, dm.Name, "", false)
}
}
// sendRelease sends a release message to a node that previously granted a lock
func sendRelease(c NetLocker, name, uid string, isReadLock bool) {
backOffArray := []time.Duration{
30 * time.Second, // 30 secs
1 * time.Minute, // 1 min
3 * time.Minute, // 3 min
10 * time.Minute, // 10 min
30 * time.Minute, // 30 min
1 * time.Hour, // 1 hour
}
go func(c NetLocker, name string) {
for _, backOff := range backOffArray {
// All client methods issuing RPCs are thread-safe and goroutine-safe,
// i.e. it is safe to call them from multiple concurrently running goroutines.
args := LockArgs{
UID: uid,
Resource: name,
ServerAddr: clnts[ownNode].ServerAddr(),
ServiceEndpoint: clnts[ownNode].ServiceEndpoint(),
}
var err error
if len(uid) == 0 {
if _, err = c.ForceUnlock(args); err != nil {
log("Unable to call ForceUnlock", err)
}
} else if isReadLock {
if _, err = c.RUnlock(args); err != nil {
log("Unable to call RUnlock", err)
}
} else {
if _, err = c.Unlock(args); err != nil {
log("Unable to call Unlock", err)
}
}
if err != nil {
// Ignore if err is net.Error and it is occurred due to timeout.
// The cause could have been server timestamp mismatch or server may have restarted.
// FIXME: This is minio specific behaviour and we would need a way to make it generically.
if nErr, ok := err.(net.Error); ok && nErr.Timeout() {
err = nil
}
}
if err == nil {
return
}
// Wait..
time.Sleep(backOff)
}
}(c, name)
}
// DRLocker returns a sync.Locker interface that implements
// the Lock and Unlock methods by calling drw.RLock and drw.RUnlock.
func (dm *DRWMutex) DRLocker() sync.Locker {
return (*drlocker)(dm)
}
type drlocker DRWMutex
func (dr *drlocker) Lock() { (*DRWMutex)(dr).RLock() }
func (dr *drlocker) Unlock() { (*DRWMutex)(dr).RUnlock() }
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