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|
package leadership
import (
"errors"
"github.com/docker/libkv/store"
)
// Follower can follow an election in real-time and push notifications whenever
// there is a change in leadership.
type Follower struct {
client store.Store
key string
leader string
leaderCh chan string
stopCh chan struct{}
errCh chan error
}
// NewFollower creates a new follower.
func NewFollower(client store.Store, key string) *Follower {
return &Follower{
client: client,
key: key,
stopCh: make(chan struct{}),
}
}
// Leader returns the current leader.
func (f *Follower) Leader() string {
return f.leader
}
// FollowElection starts monitoring the election.
func (f *Follower) FollowElection() (<-chan string, <-chan error) {
f.leaderCh = make(chan string)
f.errCh = make(chan error)
go f.follow()
return f.leaderCh, f.errCh
}
// Stop stops monitoring an election.
func (f *Follower) Stop() {
close(f.stopCh)
}
func (f *Follower) follow() {
defer close(f.leaderCh)
defer close(f.errCh)
ch, err := f.client.Watch(f.key, f.stopCh)
if err != nil {
f.errCh <- err
}
f.leader = ""
for kv := range ch {
if kv == nil {
continue
}
curr := string(kv.Value)
if curr == f.leader {
continue
}
f.leader = curr
f.leaderCh <- f.leader
}
// Channel closed, we return an error
f.errCh <- errors.New("Leader Election: watch leader channel closed, the store may be unavailable...")
}
|
