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zkrwlock.go
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zkrwlock.go
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package cypress
import (
"context"
"strings"
"sync"
"sync/atomic"
"github.com/go-zookeeper/zk"
"github.com/google/uuid"
"go.uber.org/zap"
)
const (
readersParentNode = "readers"
writerNode = "writer"
)
// ZkRWLock zookeeper based reader/writer lock
type ZkRWLock struct {
conn *zk.Conn
path string
readerPath string
writerPath string
lock *sync.Mutex
readers int32
readerLockAcquired bool
writerLockAcquired bool
localLock *sync.RWMutex
}
// NewZkRWLock creates a zookeeper reader/writer lock on the given path
func NewZkRWLock(conn *zk.Conn, path string) (*ZkRWLock, error) {
_, err := conn.Create(path, []byte{}, 0, zk.WorldACL(zk.PermAll))
if err != nil && err != zk.ErrNodeExists {
return nil, err
}
if !strings.HasSuffix(path, "/") {
path = path + "/"
}
_, err = conn.Create(path+readersParentNode, []byte{}, 0, zk.WorldACL(zk.PermAll))
if err != nil && err != zk.ErrNodeExists {
return nil, err
}
return &ZkRWLock{conn, path, path + readersParentNode + "/" + uuid.NewString(), path + writerNode, &sync.Mutex{}, 0, false, false, &sync.RWMutex{}}, nil
}
// RLock try to acquire reader lock
func (rwLock *ZkRWLock) RLock(ctx context.Context) (LockContext, error) {
rwLock.localLock.RLock()
releaseLocalLock := false
cleanupReaderNode := false
defer func() {
if cleanupReaderNode {
if cleanupErr := rwLock.conn.Delete(rwLock.readerPath, -1); cleanupErr != nil {
zap.L().Fatal("!!!failed to cleanup reader node, writers will be hungry", zap.Error(cleanupErr), zap.String("node", rwLock.readerPath), zap.String("trace", GetTraceID(ctx)))
}
}
if releaseLocalLock {
rwLock.localLock.RUnlock()
}
}()
rwLock.lock.Lock()
defer rwLock.lock.Unlock()
if rwLock.readerLockAcquired {
atomic.AddInt32(&rwLock.readers, 1)
return nil, nil
}
var cancelled int32
cancelChannel := make(chan int32, 1)
defer close(cancelChannel)
go func() {
select {
case <-ctx.Done():
if ctx.Err() == context.DeadlineExceeded || ctx.Err() == context.Canceled {
atomic.StoreInt32(&cancelled, 1)
cancelChannel <- 1
}
case <-cancelChannel:
}
}()
for atomic.LoadInt32(&cancelled) == 0 {
// 1. Create reader node
_, err := rwLock.conn.Create(rwLock.readerPath, []byte{}, zk.FlagEphemeral, zk.WorldACL(zk.PermAll))
if err != nil {
releaseLocalLock = true
if err == zk.ErrNodeExists {
zap.L().Error("trying to acquire reader lock while it's acquired", zap.String("node", rwLock.readerPath), zap.String("trace", GetTraceID(ctx)), zap.Error(err))
}
return nil, err
}
// Need to cleanup reader node in case of failure
cleanupReaderNode = true
// 2. Check writer node
exists, _, ch, err := rwLock.conn.ExistsW(rwLock.writerPath)
if err != nil {
releaseLocalLock = true
zap.L().Error("failed to check writer node", zap.String("node", rwLock.writerPath), zap.String("trace", GetTraceID(ctx)), zap.Error(err))
return nil, err
}
// Node does not exist, reader lock acquired
if !exists {
rwLock.readerLockAcquired = true
cleanupReaderNode = false
atomic.AddInt32(&rwLock.readers, 1)
return nil, nil
}
// Node exists
// 3. Delete reader node
err = rwLock.conn.Delete(rwLock.readerPath, -1)
if err != nil {
releaseLocalLock = true
zap.L().Fatal("!!!failed to release reader node, writers will be hungry", zap.String("node", rwLock.readerPath), zap.Error(err), zap.String("trace", GetTraceID(ctx)))
return nil, err
}
// Reader node has already deleted, no need to cleanup
cleanupReaderNode = false
select {
case event := <-ch:
if event.Type != zk.EventNodeDeleted {
releaseLocalLock = true
zap.L().Error("unexpected reader watch event", zap.Int32("event", int32(event.Type)), zap.String("reader", rwLock.readerPath), zap.String("trace", GetTraceID(ctx)))
return nil, ErrLockFailed
}
case <-cancelChannel:
}
}
// Lock cancelled
releaseLocalLock = true
return nil, ErrLockCancelled
}
// RUnlock release reader lock that is acquired
func (rwLock *ZkRWLock) RUnlock(lockCtx LockContext) {
// release local lock
rwLock.localLock.RUnlock()
// if no more local readers, release zk reader node
rwLock.lock.Lock()
defer rwLock.lock.Unlock()
if rwLock.readerLockAcquired && atomic.AddInt32(&rwLock.readers, -1) == 0 {
rwLock.readerLockAcquired = false
err := rwLock.conn.Delete(rwLock.readerPath, -1)
if err != nil {
zap.L().Fatal("!!!unable to delete reader node, writers will be hungry", zap.Error(err))
}
}
}
// Lock acquires writer lock
func (rwLock *ZkRWLock) Lock(ctx context.Context) (LockContext, error) {
rwLock.localLock.Lock()
releaseLocalLock := false
cleanupWriterNode := false
defer func() {
if cleanupWriterNode {
if cleanupErr := rwLock.conn.Delete(rwLock.writerPath, -1); cleanupErr != nil {
zap.L().Fatal("!!!failed to cleanup writer node, no lock can be acquired", zap.Error(cleanupErr), zap.String("node", rwLock.writerPath), zap.String("trace", GetTraceID(ctx)))
}
}
if releaseLocalLock {
rwLock.localLock.Unlock()
}
}()
rwLock.lock.Lock()
defer rwLock.lock.Unlock()
var cancelled int32
cancelChannel := make(chan int32, 1)
defer close(cancelChannel)
go func() {
select {
case <-ctx.Done():
if ctx.Err() == context.DeadlineExceeded || ctx.Err() == context.Canceled {
atomic.StoreInt32(&cancelled, 1)
cancelChannel <- 1
}
case <-cancelChannel:
break
}
}()
for atomic.LoadInt32(&cancelled) == 0 {
// 1. Check writer node
exists, _, ch, err := rwLock.conn.ExistsW(rwLock.writerPath)
if err != nil {
releaseLocalLock = true
zap.L().Error("failed to check writer node exists", zap.String("node", rwLock.writerPath), zap.Error(err), zap.String("trace", GetTraceID(ctx)))
return nil, err
}
if exists {
select {
case event := <-ch:
if event.Type != zk.EventNodeDeleted {
releaseLocalLock = true
zap.L().Error("unexpected node event", zap.String("node", rwLock.writerPath), zap.Int32("event", int32(event.Type)), zap.String("trace", GetTraceID(ctx)))
return nil, ErrLockFailed
}
break
case <-cancelChannel:
releaseLocalLock = true
return nil, ErrLockCancelled
}
}
// 2. Create writer node
_, err = rwLock.conn.Create(rwLock.writerPath, []byte{}, zk.FlagEphemeral, zk.WorldACL(zk.PermAll))
if err == zk.ErrNodeExists {
continue
}
if err != nil {
releaseLocalLock = true
zap.L().Error("failed to create writer node", zap.String("node", rwLock.writerPath), zap.Error(err), zap.String("trace", GetTraceID(ctx)))
return nil, err
}
// Need to cleanup writer node in case of failure
cleanupWriterNode = true
// write node created
// 3. Wait for readers if any
for atomic.LoadInt32(&cancelled) == 0 {
readers, _, readersCh, err := rwLock.conn.ChildrenW(rwLock.path + readersParentNode)
if err != nil {
releaseLocalLock = true
zap.L().Error("failed to check readers", zap.String("node", rwLock.path+readersParentNode), zap.Error(err), zap.String("trace", GetTraceID(ctx)))
return nil, err
}
if len(readers) == 0 {
// lock acquired
cleanupWriterNode = false
rwLock.writerLockAcquired = true
return nil, nil
}
select {
case event := <-readersCh:
if event.Type != zk.EventNodeChildrenChanged {
zap.L().Error("unexpected node event", zap.String("node", rwLock.writerPath), zap.Int32("event", int32(event.Type)), zap.String("trace", GetTraceID(ctx)))
}
case <-cancelChannel:
releaseLocalLock = true
return nil, ErrLockCancelled
}
}
}
// Lock cancelled
releaseLocalLock = true
return nil, ErrLockCancelled
}
// Unlock release writer lock
func (rwLock *ZkRWLock) Unlock(lockCtx LockContext) {
rwLock.localLock.Unlock()
rwLock.lock.Lock()
defer rwLock.lock.Unlock()
rwLock.writerLockAcquired = false
err := rwLock.conn.Delete(rwLock.writerPath, -1)
if err != nil {
zap.L().Fatal("!!!failed to delete writer node, no more lock can be granted", zap.String("node", rwLock.writerPath), zap.Error(err))
}
}