leadership: API cleanup.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

leadership/README.md

@@ -19,11 +19,12 @@ if err != nil {
 underwood := leadership.NewCandidate(client, "service/swarm/leader", "underwood")
 underwood.RunForElection()
 
-for elected := range underwood.ElectedCh {
+electedCh := underwood.ElectedCh()
+for isElected := range rlectedCh {
 	// This loop will run every time there is a change in our leadership
 	// status.
 
-	if elected {
+	if isElected {
 		// We won the election - we are now the leader.
 		// Let's do leader stuff, for example, sleep for a while.
 		log.Printf("I won the election! I'm now the leader")
@@ -48,7 +49,8 @@ there is a change in leadership:
 ```go
 follower := leadership.NewFollower(client, "service/swarm/leader")
 follower.FollowElection()
-for leader := <-follower.LeaderCh {
+leaderCh := follower.LeaderCh()
+for leader := <-leaderCh {
 	// Leader is a string containing the value passed to `NewCandidate`.
 	log.Printf("%s is now the leader", leader)
 }

leadership/candidate.go

@@ -9,16 +9,15 @@ import (
 
 // Candidate runs the leader election algorithm asynchronously
 type Candidate struct {
-	ElectedCh chan bool
-
 	client store.Store
 	key    string
 	node   string
 
-	lock     sync.Mutex
+	electedCh chan bool
-	leader   bool
+	lock      sync.Mutex
-	stopCh   chan struct{}
+	leader    bool
-	resignCh chan bool
+	stopCh    chan struct{}
+	resignCh  chan bool
 }
 
 // NewCandidate creates a new Candidate
@@ -28,13 +27,20 @@ func NewCandidate(client store.Store, key, node string) *Candidate {
 		key:    key,
 		node:   node,
 
-		ElectedCh: make(chan bool),
+		electedCh: make(chan bool),
 		leader:    false,
 		resignCh:  make(chan bool),
 		stopCh:    make(chan struct{}),
 	}
 }
 
+// ElectedCh is used to get a channel which delivers signals on
+// acquiring or losing leadership. It sends true if we become
+// the leader, and false if we lose it.
+func (c *Candidate) ElectedCh() <-chan bool {
+	return c.electedCh
+}
+
 // RunForElection starts the leader election algorithm. Updates in status are
 // pushed through the ElectedCh channel.
 func (c *Candidate) RunForElection() error {
@@ -70,12 +76,12 @@ func (c *Candidate) update(status bool) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
-	c.ElectedCh <- status
+	c.electedCh <- status
 	c.leader = status
 }
 
 func (c *Candidate) campaign(lock store.Locker) {
-	defer close(c.ElectedCh)
+	defer close(c.electedCh)
 
 	for {
 		// Start as a follower.

leadership/candidate_test.go

@@ -24,30 +24,31 @@ func TestCandidate(t *testing.T) {
 
 	candidate := NewCandidate(store, "test_key", "test_node")
 	candidate.RunForElection()
+	electedCh := candidate.ElectedCh()
 
 	// Should issue a false upon start, no matter what.
-	assert.False(t, <-candidate.ElectedCh)
+	assert.False(t, <-electedCh)
 
 	// Since the lock always succeeeds, we should get elected.
-	assert.True(t, <-candidate.ElectedCh)
+	assert.True(t, <-electedCh)
 
 	// Signaling a lost lock should get us de-elected...
 	close(lostCh)
-	assert.False(t, <-candidate.ElectedCh)
+	assert.False(t, <-electedCh)
 
 	// And we should attempt to get re-elected again.
-	assert.True(t, <-candidate.ElectedCh)
+	assert.True(t, <-electedCh)
 
 	// When we resign, unlock will get called, we'll be notified of the
 	// de-election and we'll try to get the lock again.
 	go candidate.Resign()
-	assert.False(t, <-candidate.ElectedCh)
+	assert.False(t, <-electedCh)
-	assert.True(t, <-candidate.ElectedCh)
+	assert.True(t, <-electedCh)
 
 	// After stopping the candidate, the ElectedCh should be closed.
 	candidate.Stop()
 	select {
-	case <-candidate.ElectedCh:
+	case <-electedCh:
 		assert.True(t, false) // we should not get here.
 	default:
 		assert.True(t, true)

leadership/follower.go

@@ -5,26 +5,30 @@ import "github.com/docker/swarm/pkg/store"
 // Follower can folow an election in real-time and push notifications whenever
 // there is a change in leadership.
 type Follower struct {
-	LeaderCh chan string
-
 	client store.Store
 	key    string
 
-	stopCh chan struct{}
+	leaderCh chan string
+	stopCh   chan struct{}
 }
 
 // NewFollower creates a new follower.
 func NewFollower(client store.Store, key string) *Follower {
 	return &Follower{
-		LeaderCh: make(chan string),
 		client:   client,
 		key:      key,
+		leaderCh: make(chan string),
 		stopCh:   make(chan struct{}),
 	}
 }
 
-// FollowElection starts monitoring the election. The current leader is updated
+// LeaderCh is used to get a channel which delivers the currently elected
-// in real-time and pushed through `LeaderCh`.
+// leader.
+func (f *Follower) LeaderCh() <-chan string {
+	return f.leaderCh
+}
+
+// FollowElection starts monitoring the election.
 func (f *Follower) FollowElection() error {
 	ch, err := f.client.Watch(f.key, f.stopCh)
 	if err != nil {
@@ -42,7 +46,7 @@ func (f *Follower) Stop() {
 }
 
 func (f *Follower) follow(<-chan *store.KVPair) {
-	defer close(f.LeaderCh)
+	defer close(f.leaderCh)
 
 	// FIXME: We should pass `RequireConsistent: true` to Consul.
 	ch, err := f.client.Watch(f.key, f.stopCh)
@@ -57,6 +61,6 @@ func (f *Follower) follow(<-chan *store.KVPair) {
 			continue
 		}
 		prev = curr
-		f.LeaderCh <- string(curr)
+		f.leaderCh <- string(curr)
 	}
 }

leadership/follower_test.go

@@ -20,6 +20,7 @@ func TestFollower(t *testing.T) {
 
 	follower := NewFollower(store, "test_key")
 	follower.FollowElection()
+	leaderCh := follower.LeaderCh()
 
 	// Simulate leader updates
 	go func() {
@@ -30,14 +31,14 @@ func TestFollower(t *testing.T) {
 	}()
 
 	// We shouldn't see duplicate events.
-	assert.Equal(t, <-follower.LeaderCh, "leader1")
+	assert.Equal(t, <-leaderCh, "leader1")
-	assert.Equal(t, <-follower.LeaderCh, "leader2")
+	assert.Equal(t, <-leaderCh, "leader2")
-	assert.Equal(t, <-follower.LeaderCh, "leader1")
+	assert.Equal(t, <-leaderCh, "leader1")
 
 	// Once stopped, iteration over the leader channel should stop.
 	follower.Stop()
 	close(kvCh)
-	assert.Equal(t, "", <-follower.LeaderCh)
+	assert.Equal(t, "", <-leaderCh)
 
 	mockStore.AssertExpectations(t)
 }