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// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package runner
import (
"context"
"errors"
"fmt"
"go.etcd.io/etcd/client/v3/concurrency"
"github.com/spf13/cobra"
)
// NewElectionCommand returns the cobra command for "election runner".
func NewElectionCommand() *cobra.Command {
cmd := &cobra.Command{
Use: "election [election name (defaults to 'elector')]",
Short: "Performs election operation",
Run: runElectionFunc,
}
cmd.Flags().IntVar(&totalClientConnections, "total-client-connections", 10, "total number of client connections")
return cmd
}
func runElectionFunc(cmd *cobra.Command, args []string) {
election := "elector"
if len(args) == 1 {
election = args[0]
}
if len(args) > 1 {
ExitWithError(ExitBadArgs, errors.New("election takes at most one argument"))
}
rcs := make([]roundClient, totalClientConnections)
validatec := make(chan struct{}, len(rcs))
// nextc closes when election is ready for next round.
nextc := make(chan struct{})
eps := endpointsFromFlag(cmd)
for i := range rcs {
v := fmt.Sprintf("%d", i)
observedLeader := ""
validateWaiters := 0
var rcNextc chan struct{}
setRcNextc := func() {
rcNextc = nextc
}
rcs[i].c = newClient(eps, dialTimeout)
var (
s *concurrency.Session
err error
)
for {
s, err = concurrency.NewSession(rcs[i].c)
if err == nil {
break
}
}
e := concurrency.NewElection(s, election)
rcs[i].acquire = func() (err error) {
ctx, cancel := context.WithCancel(context.Background())
donec := make(chan struct{})
go func() {
defer close(donec)
for ctx.Err() == nil {
if ol, ok := <-e.Observe(ctx); ok {
observedLeader = string(ol.Kvs[0].Value)
break
}
}
if observedLeader != v {
cancel()
}
}()
err = e.Campaign(ctx, v)
cancel()
<-donec
if err == nil {
observedLeader = v
}
if observedLeader == v {
validateWaiters = len(rcs)
}
select {
case <-ctx.Done():
return nil
default:
return err
}
}
rcs[i].validate = func() error {
l, err := e.Leader(context.TODO())
if err == nil && string(l.Kvs[0].Value) != observedLeader {
return fmt.Errorf("expected leader %q, got %q", observedLeader, l.Kvs[0].Value)
}
if err != nil {
return err
}
setRcNextc()
validatec <- struct{}{}
return nil
}
rcs[i].release = func() error {
for validateWaiters > 0 {
select {
case <-validatec:
validateWaiters--
default:
return fmt.Errorf("waiting on followers")
}
}
if err := e.Resign(context.TODO()); err != nil {
return err
}
if observedLeader == v {
oldNextc := nextc
nextc = make(chan struct{})
close(oldNextc)
}
<-rcNextc
observedLeader = ""
return nil
}
}
// each client creates 1 key from Campaign() and delete it from Resign()
// a round involves in 2*len(rcs) requests.
doRounds(rcs, rounds, 2*len(rcs))
}
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