The library to syncronize app nodes by using zookeeper backend.
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nodesync/nodesync.go

179 lines
3.6 KiB

package sync
import (
"path"
"github.com/go-zookeeper/zk"
)
// NodeSync structure
type NodeSync struct {
Zk *zk.Conn
rootPath string
}
// Inside private environment keep everything open
var defaultAcl = zk.WorldACL(zk.PermAll)
// The length of a postfix sequence, see http://zookeeper.apache.org/doc/current/zookeeperProgrammers.html#Sequence+Nodes+--+Unique+Naming
var sequenceLen = 10
// Name is used by default to create keys
var defaultKey = "sync"
// New creates a new nodesync instance
func New(zkconn *zk.Conn, rootPath string) (nodeSync *NodeSync, err error) {
nodeSync = &NodeSync{Zk: zkconn, rootPath: rootPath}
err = nodeSync.createRecursively(rootPath, defaultAcl)
if err != nil {
nodeSync = nil
}
return
}
// Fetch returns node data
func (s *NodeSync) Fetch(where string, key string) (current []byte, err error) {
workingPath := path.Join(s.rootPath, where, key)
current, _, err = s.Zk.Get(workingPath)
return
}
// FetchAndSet replaces zookeeper key with new value bytes and returns old if exists
func (s *NodeSync) FetchAndSet(where string, key string, value []byte) (old []byte, err error) {
workingPath := path.Join(s.rootPath, where, key)
err = s.createRecursively(workingPath, defaultAcl)
if err != nil {
return
}
var ver int32 = -1
old, stat, err := s.Zk.Get(workingPath)
if err == nil {
ver = stat.Version
}
_, err = s.Zk.Set(workingPath, value, ver)
return old, err
}
// Lock creates zookeeper ephemeral key to ensure itself in the node list.
// This is used by the locking mechanism to emulate mutex in a cluster.
func (s *NodeSync) Lock(where string) (iam string, err error) {
workingPath := path.Join(s.rootPath, where)
err = s.createRecursively(workingPath, defaultAcl)
if err != nil {
return
}
created, err := s.Zk.CreateProtectedEphemeralSequential(path.Join(workingPath, defaultKey), nil, defaultAcl)
if err != nil {
return
}
_, iam = path.Split(created)
return
}
// Unlock waits for the previous worker be unlocked, then removes itself
func (s *NodeSync) Unlock(where string, iam string) (err error) {
workingPath := path.Join(s.rootPath, where)
children, _, err := s.Zk.Children(workingPath)
if err != nil {
return err
}
if len(children) == 0 {
return
}
children = sortChildren(children)
locked := children[0]
if locked == iam {
err = s.Zk.Delete(path.Join(workingPath, iam), 0)
return
}
for i := 1; i < len(children); i++ {
if children[i] == iam {
break
}
locked = children[i]
}
for {
var exists bool
var ev <-chan zk.Event
exists, _, ev, err = s.Zk.ExistsW(path.Join(workingPath, locked))
if err != nil {
return
}
if !exists {
break
}
change := <-ev
if change.Type == zk.EventNodeDeleted {
break
}
}
err = s.Zk.Delete(path.Join(workingPath, iam), 0)
return
}
// WaitEmpty implements a barrier synchronisation mechanism by waiting for empty node.
func (s *NodeSync) WaitEmpty(where string) (err error) {
workingPath := path.Join(s.rootPath, where)
for {
var children []string
var ev <-chan zk.Event
children, _, ev, err = s.Zk.ChildrenW(workingPath)
if err != nil {
return
}
if len(children) == 0 {
break
}
<-ev
}
return
}
// WaitChanged waits for any changes a zookeeper node and returns a new children list after the change.
// Note: the children list is always stable sorted.
func (s *NodeSync) WaitChanged(where string) (children []string, ev <-chan zk.Event, err error) {
workingPath := path.Join(s.rootPath, where)
children, _, ev, err = s.Zk.ChildrenW(workingPath)
if err != nil {
return
}
children = sortChildren(children)
return
}