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