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election_command.go
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/
election_command.go
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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 command
import (
"context"
"errors"
"fmt"
"github.com/coreos/etcd/clientv3/concurrency"
"github.com/spf13/cobra"
)
// NewElectionCommand returns the cobra command for "election runner".
func NewElectionCommand() *cobra.Command {
cmd := &cobra.Command{
Use: "election",
Short: "Performs election operation",
Run: runElectionFunc,
}
cmd.Flags().IntVar(&rounds, "rounds", 100, "number of rounds to run")
cmd.Flags().IntVar(&totalClientConnections, "total-client-connections", 10, "total number of client connections")
return cmd
}
func runElectionFunc(cmd *cobra.Command, args []string) {
if len(args) > 0 {
ExitWithError(ExitBadArgs, errors.New("election does not take any argument"))
}
rcs := make([]roundClient, totalClientConnections)
validatec, releasec := make(chan struct{}, len(rcs)), make(chan struct{}, len(rcs))
for range rcs {
releasec <- struct{}{}
}
eps := endpointsFromFlag(cmd)
dialTimeout := dialTimeoutFromCmd(cmd)
for i := range rcs {
v := fmt.Sprintf("%d", i)
observedLeader := ""
validateWaiters := 0
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, "electors")
rcs[i].acquire = func() error {
<-releasec
ctx, cancel := context.WithCancel(context.Background())
go func() {
if ol, ok := <-e.Observe(ctx); ok {
observedLeader = string(ol.Kvs[0].Value)
if observedLeader != v {
cancel()
}
}
}()
err = e.Campaign(ctx, v)
if err == nil {
observedLeader = v
}
if observedLeader == v {
validateWaiters = len(rcs)
}
select {
case <-ctx.Done():
return nil
default:
cancel()
return err
}
}
rcs[i].validate = func() error {
if l, err := e.Leader(context.TODO()); err == nil && l != observedLeader {
return fmt.Errorf("expected leader %q, got %q", observedLeader, l)
}
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 {
for range rcs {
releasec <- struct{}{}
}
}
observedLeader = ""
return nil
}
}
doRounds(rcs, rounds)
}