150 lines
3 KiB
Go
150 lines
3 KiB
Go
package zk
|
|
|
|
import (
|
|
"errors"
|
|
"fmt"
|
|
"strconv"
|
|
"strings"
|
|
)
|
|
|
|
var (
|
|
// ErrDeadlock is returned by Lock when trying to lock twice without unlocking first
|
|
ErrDeadlock = errors.New("zk: trying to acquire a lock twice")
|
|
// ErrNotLocked is returned by Unlock when trying to release a lock that has not first be acquired.
|
|
ErrNotLocked = errors.New("zk: not locked")
|
|
)
|
|
|
|
// Lock is a mutual exclusion lock.
|
|
type Lock struct {
|
|
c *Conn
|
|
path string
|
|
acl []ACL
|
|
lockPath string
|
|
seq int
|
|
}
|
|
|
|
// NewLock creates a new lock instance using the provided connection, path, and acl.
|
|
// The path must be a node that is only used by this lock. A lock instances starts
|
|
// unlocked until Lock() is called.
|
|
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])
|
|
}
|
|
|
|
// Lock attempts to acquire the lock. It will wait to return until the lock
|
|
// is acquired or an error occurs. If this instance already has the lock
|
|
// then ErrDeadlock is returned.
|
|
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:] {
|
|
var exists bool
|
|
pth += "/" + p
|
|
exists, _, err = l.c.Exists(pth)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if exists == true {
|
|
continue
|
|
}
|
|
_, 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 := -1
|
|
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
|
|
}
|
|
|
|
// Unlock releases an acquired lock. If the lock is not currently acquired by
|
|
// this Lock instance than ErrNotLocked is returned.
|
|
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
|
|
}
|