concurrency: add examples

clientv3/concurrency/example_election_test.go

@@ -0,0 +1,90 @@
+// Copyright 2017 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 concurrency_test
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"sync"
+	"time"
+
+	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
+)
+
+func ExampleElection_Campaign() {
+	cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer cli.Close()
+
+	// create two separate sessions for election competition
+	s1, err := concurrency.NewSession(cli)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer s1.Close()
+	e1 := concurrency.NewElection(s1, "/my-election/")
+
+	s2, err := concurrency.NewSession(cli)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer s2.Close()
+	e2 := concurrency.NewElection(s2, "/my-election/")
+
+	// create competing candidates, with e1 initially losing to e2
+	var wg sync.WaitGroup
+	wg.Add(2)
+	electc := make(chan *concurrency.Election, 2)
+	go func() {
+		defer wg.Done()
+		// delay candidacy so e2 wins first
+		time.Sleep(3 * time.Second)
+		if err := e1.Campaign(context.Background(), "e1"); err != nil {
+			log.Fatal(err)
+		}
+		electc <- e1
+	}()
+	go func() {
+		defer wg.Done()
+		if err := e2.Campaign(context.Background(), "e2"); err != nil {
+			log.Fatal(err)
+		}
+		electc <- e2
+	}()
+
+	cctx, cancel := context.WithCancel(context.TODO())
+	defer cancel()
+
+	e := <-electc
+	fmt.Println("completed first election with", string((<-e.Observe(cctx)).Kvs[0].Value))
+
+	// resign so next candidate can be elected
+	if err := e.Resign(context.TODO()); err != nil {
+		log.Fatal(err)
+	}
+
+	e = <-electc
+	fmt.Println("completed second election with", string((<-e.Observe(cctx)).Kvs[0].Value))
+
+	wg.Wait()
+
+	// Output:
+	// completed first election with e2
+	// completed second election with e1
+}