mirror of
https://github.com/etcd-io/etcd.git
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109 lines
2.8 KiB
Go
109 lines
2.8 KiB
Go
// Copyright 2016 CoreOS, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package recipe
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import (
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"github.com/coreos/etcd/clientv3"
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"github.com/coreos/etcd/etcdserver"
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"github.com/coreos/etcd/storage/storagepb"
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)
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type Election struct {
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client *clientv3.Client
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keyPrefix string
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leaderKey *EphemeralKV
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}
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// NewElection returns a new election on a given key prefix.
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func NewElection(client *clientv3.Client, keyPrefix string) *Election {
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return &Election{client, keyPrefix, nil}
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}
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// Volunteer puts a value as elegible for the election. It blocks until
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// it is elected or an error occurs (cannot withdraw candidacy)
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func (e *Election) Volunteer(val string) error {
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if e.leaderKey != nil {
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return e.leaderKey.Put(val)
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}
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myKey, err := NewUniqueEphemeralKV(e.client, e.keyPrefix, val)
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if err != nil {
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return err
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}
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if err = e.waitLeadership(myKey); err != nil {
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return err
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}
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e.leaderKey = myKey
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return nil
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}
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// Resign lets a leader start a new election.
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func (e *Election) Resign() (err error) {
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if e.leaderKey != nil {
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err = e.leaderKey.Delete()
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e.leaderKey = nil
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}
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return err
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}
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// Leader returns the leader value for the current election.
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func (e *Election) Leader() (string, error) {
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resp, err := NewRange(e.client, e.keyPrefix).FirstCreate()
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if err != nil {
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return "", err
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} else if len(resp.Kvs) == 0 {
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// no leader currently elected
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return "", etcdserver.ErrNoLeader
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}
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return string(resp.Kvs[0].Value), nil
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}
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// Wait waits for a leader to be elected, returning the leader value.
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func (e *Election) Wait() (string, error) {
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resp, err := NewRange(e.client, e.keyPrefix).FirstCreate()
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if err != nil {
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return "", err
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} else if len(resp.Kvs) != 0 {
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// leader already exists
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return string(resp.Kvs[0].Value), nil
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}
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_, err = WaitPrefixEvents(
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e.client,
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e.keyPrefix,
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resp.Header.Revision,
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[]storagepb.Event_EventType{storagepb.PUT})
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if err != nil {
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return "", err
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}
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return e.Wait()
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}
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func (e *Election) waitLeadership(tryKey *EphemeralKV) error {
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resp, err := NewRangeRev(
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e.client,
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e.keyPrefix,
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tryKey.Revision()-1).LastCreate()
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if err != nil {
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return err
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} else if len(resp.Kvs) == 0 {
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// nothing before tryKey => have leadership
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return nil
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}
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_, err = WaitEvents(
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e.client,
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string(resp.Kvs[0].Key),
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tryKey.Revision(),
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[]storagepb.Event_EventType{storagepb.DELETE})
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return err
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}
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