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|
package zk
import (
"errors"
"fmt"
"strconv"
"strings"
)
var (
ErrDeadlock = errors.New("zk: trying to acquire a lock twice")
ErrNotLocked = errors.New("zk: not locked")
)
type Lock struct {
c *Conn
path string
acl []ACL
lockPath string
seq int
}
func NewLock(c *Conn, path string, acl []ACL) *Lock {
return &Lock{
c: c,
path: path,
acl: acl,
}
}
func parseSeq(path string) (int, error) {
parts := strings.Split(path, "-")
return strconv.Atoi(parts[len(parts)-1])
}
func (l *Lock) Lock() error {
if l.lockPath != "" {
return ErrDeadlock
}
prefix := fmt.Sprintf("%s/lock-", l.path)
path := ""
var err error
for i := 0; i < 3; i++ {
path, err = l.c.CreateProtectedEphemeralSequential(prefix, []byte{}, l.acl)
if err == ErrNoNode {
// Create parent node.
parts := strings.Split(l.path, "/")
pth := ""
for _, p := range parts[1:] {
pth += "/" + p
_, err := l.c.Create(pth, []byte{}, 0, l.acl)
if err != nil && err != ErrNodeExists {
return err
}
}
} else if err == nil {
break
} else {
return err
}
}
if err != nil {
return err
}
seq, err := parseSeq(path)
if err != nil {
return err
}
for {
children, _, err := l.c.Children(l.path)
if err != nil {
return err
}
lowestSeq := seq
prevSeq := 0
prevSeqPath := ""
for _, p := range children {
s, err := parseSeq(p)
if err != nil {
return err
}
if s < lowestSeq {
lowestSeq = s
}
if s < seq && s > prevSeq {
prevSeq = s
prevSeqPath = p
}
}
if seq == lowestSeq {
// Acquired the lock
break
}
// Wait on the node next in line for the lock
_, _, ch, err := l.c.GetW(l.path + "/" + prevSeqPath)
if err != nil && err != ErrNoNode {
return err
} else if err != nil && err == ErrNoNode {
// try again
continue
}
ev := <-ch
if ev.Err != nil {
return ev.Err
}
}
l.seq = seq
l.lockPath = path
return nil
}
func (l *Lock) Unlock() error {
if l.lockPath == "" {
return ErrNotLocked
}
if err := l.c.Delete(l.lockPath, -1); err != nil {
return err
}
l.lockPath = ""
l.seq = 0
return nil
}
|
