Golang concurrency.NewElection函数代码示例

// TestElectionSessionRelock ensures that campaigning twice on the same election
// with the same lock will Proclaim instead of deadlocking.
func TestElectionSessionRecampaign(t *testing.T) {
	clus := NewClusterV3(t, &ClusterConfig{Size: 1})
	defer clus.Terminate(t)
	cli := clus.RandClient()

	session, err := concurrency.NewSession(cli)
	if err != nil {
		t.Error(err)
	}
	defer session.Orphan()

	e := concurrency.NewElection(session, "test-elect")
	if err := e.Campaign(context.TODO(), "abc"); err != nil {
		t.Fatal(err)
	}
	e2 := concurrency.NewElection(session, "test-elect")
	if err := e2.Campaign(context.TODO(), "def"); err != nil {
		t.Fatal(err)
	}

	ctx, cancel := context.WithCancel(context.TODO())
	defer cancel()
	if resp := <-e.Observe(ctx); len(resp.Kvs) == 0 || string(resp.Kvs[0].Value) != "def" {
		t.Fatalf("expected value=%q, got response %v", "def", resp)
	}
}

// TestElectionFailover tests that an election will
func TestElectionFailover(t *testing.T) {
	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
	defer clus.Terminate(t)
	defer dropSessionLease(clus)

	cctx, cancel := context.WithCancel(context.TODO())
	defer cancel()

	// first leader (elected)
	e := concurrency.NewElection(clus.clients[0], "test-election")
	if err := e.Campaign(context.TODO(), "foo"); err != nil {
		t.Fatalf("failed volunteer (%v)", err)
	}

	// check first leader
	resp, ok := <-e.Observe(cctx)
	if !ok {
		t.Fatalf("could not wait for first election; channel closed")
	}
	s := string(resp.Kvs[0].Value)
	if s != "foo" {
		t.Fatalf("wrong election result. got %s, wanted foo", s)
	}

	// next leader
	electedc := make(chan struct{})
	go func() {
		ee := concurrency.NewElection(clus.clients[1], "test-election")
		if eer := ee.Campaign(context.TODO(), "bar"); eer != nil {
			t.Fatal(eer)
		}
		electedc <- struct{}{}
	}()

	// invoke leader failover
	session, serr := concurrency.NewSession(clus.clients[0])
	if serr != nil {
		t.Fatal(serr)
	}
	if err := session.Close(); err != nil {
		t.Fatal(err)
	}

	// check new leader
	e = concurrency.NewElection(clus.clients[2], "test-election")
	resp, ok = <-e.Observe(cctx)
	if !ok {
		t.Fatalf("could not wait for second election; channel closed")
	}
	s = string(resp.Kvs[0].Value)
	if s != "bar" {
		t.Fatalf("wrong election result. got %s, wanted bar", s)
	}

	// leader must ack election (otherwise, Campaign may see closed conn)
	<-electedc
}

func observe(c *clientv3.Client, election string) error {
	e := concurrency.NewElection(context.TODO(), c, election)
	ctx, cancel := context.WithCancel(context.TODO())

	donec := make(chan struct{})
	sigc := make(chan os.Signal, 1)
	signal.Notify(sigc, os.Interrupt, os.Kill)
	go func() {
		<-sigc
		cancel()
	}()

	go func() {
		for resp := range e.Observe(ctx) {
			display.Get(resp)
		}
		close(donec)
	}()

	<-donec

	select {
	case <-ctx.Done():
	default:
		return errors.New("elect: observer lost")
	}

	return nil
}

func campaign(c *clientv3.Client, election string, prop string) error {
	s, err := concurrency.NewSession(c)
	if err != nil {
		return err
	}
	e := concurrency.NewElection(s, election)
	ctx, cancel := context.WithCancel(context.TODO())

	donec := make(chan struct{})
	sigc := make(chan os.Signal, 1)
	signal.Notify(sigc, os.Interrupt, os.Kill)
	go func() {
		<-sigc
		cancel()
		close(donec)
	}()

	s, serr := concurrency.NewSession(c)
	if serr != nil {
		return serr
	}

	if err = e.Campaign(ctx, prop); err != nil {
		return err
	}

	// print key since elected
	resp, err := c.Get(ctx, e.Key())
	if err != nil {
		return err
	}
	display.Get(*resp)

	select {
	case <-donec:
	case <-s.Done():
		return errors.New("elect: session expired")
	}

	return e.Resign(context.TODO())
}

// TestElectionOnPrefixOfExistingKey checks that a single
// candidate can be elected on a new key that is a prefix
// of an existing key. To wit, check for regression
// of bug #6278. https://github.com/coreos/etcd/issues/6278
//
func TestElectionOnPrefixOfExistingKey(t *testing.T) {
	clus := NewClusterV3(t, &ClusterConfig{Size: 1})
	defer clus.Terminate(t)

	cli := clus.RandClient()
	if _, err := cli.Put(context.TODO(), "testa", "value"); err != nil {
		t.Fatal(err)
	}
	s, serr := concurrency.NewSession(cli)
	if serr != nil {
		t.Fatal(serr)
	}
	e := concurrency.NewElection(s, "test")
	ctx, cancel := context.WithTimeout(context.TODO(), 5*time.Second)
	err := e.Campaign(ctx, "abc")
	cancel()
	if err != nil {
		// after 5 seconds, deadlock results in
		// 'context deadline exceeded' here.
		t.Fatal(err)
	}
}

// TestElectionWait tests if followers can correctly wait for elections.
func TestElectionWait(t *testing.T) {
	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
	defer clus.Terminate(t)
	defer dropSessionLease(clus)

	leaders := 3
	followers := 3

	electedc := make(chan string)
	nextc := []chan struct{}{}

	// wait for all elections
	donec := make(chan struct{})
	for i := 0; i < followers; i++ {
		nextc = append(nextc, make(chan struct{}))
		go func(ch chan struct{}) {
			for j := 0; j < leaders; j++ {
				b := concurrency.NewElection(clus.RandClient(), "test-election")
				cctx, cancel := context.WithCancel(context.TODO())
				defer cancel()
				s, ok := <-b.Observe(cctx)
				if !ok {
					t.Fatalf("could not observe election; channel closed")
				}
				electedc <- string(s.Kvs[0].Value)
				// wait for next election round
				<-ch
			}
			donec <- struct{}{}
		}(nextc[i])
	}

	// elect some leaders
	for i := 0; i < leaders; i++ {
		go func() {
			e := concurrency.NewElection(clus.RandClient(), "test-election")
			ev := fmt.Sprintf("electval-%v", time.Now().UnixNano())
			if err := e.Campaign(context.TODO(), ev); err != nil {
				t.Fatalf("failed volunteer (%v)", err)
			}
			// wait for followers to accept leadership
			for j := 0; j < followers; j++ {
				s := <-electedc
				if s != ev {
					t.Errorf("wrong election value got %s, wanted %s", s, ev)
				}
			}
			// let next leader take over
			if err := e.Resign(); err != nil {
				t.Fatalf("failed resign (%v)", err)
			}
			// tell followers to start listening for next leader
			for j := 0; j < followers; j++ {
				nextc[j] <- struct{}{}
			}
		}()
	}

	// wait on followers
	for i := 0; i < followers; i++ {
		<-donec
	}
}

func runElection(eps []string, rounds int) {
	rcs := make([]roundClient, 15)
	validatec, releasec := make(chan struct{}, len(rcs)), make(chan struct{}, len(rcs))
	for range rcs {
		releasec <- struct{}{}
	}

	for i := range rcs {
		v := fmt.Sprintf("%d", i)
		observedLeader := ""
		validateWaiters := 0

		rcs[i].c = randClient(eps)
		e := concurrency.NewElection(rcs[i].c, "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)
}