Revendor swarmkit to 2e956c4

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

vendor/github.com/docker/swarmkit/agent/agent.go

@@ -37,6 +37,8 @@ type Agent struct {
 	started   chan struct{}
 	startOnce sync.Once // start only once
 	ready     chan struct{}
+	leaving   chan struct{}
+	leaveOnce sync.Once
 	stopped   chan struct{} // requests shutdown
 	stopOnce  sync.Once     // only allow stop to be called once
 	closed    chan struct{} // only closed in run
@@ -53,6 +55,7 @@ func New(config *Config) (*Agent, error) {
 		config:   config,
 		sessionq: make(chan sessionOperation),
 		started:  make(chan struct{}),
+		leaving:  make(chan struct{}),
 		stopped:  make(chan struct{}),
 		closed:   make(chan struct{}),
 		ready:    make(chan struct{}),
@@ -78,6 +81,37 @@ func (a *Agent) Start(ctx context.Context) error {
 	return err
 }
 
+// Leave instructs the agent to leave the cluster. This method will shutdown
+// assignment processing and remove all assignments from the node.
+// Leave blocks until worker has finished closing all task managers or agent
+// is closed.
+func (a *Agent) Leave(ctx context.Context) error {
+	select {
+	case <-a.started:
+	default:
+		return errAgentNotStarted
+	}
+
+	a.leaveOnce.Do(func() {
+		close(a.leaving)
+	})
+
+	// agent could be closed while Leave is in progress
+	var err error
+	ch := make(chan struct{})
+	go func() {
+		err = a.worker.Wait(ctx)
+		close(ch)
+	}()
+
+	select {
+	case <-ch:
+		return err
+	case <-a.closed:
+		return ErrClosed
+	}
+}
+
 // Stop shuts down the agent, blocking until full shutdown. If the agent is not
 // started, Stop will block until the agent has fully shutdown.
 func (a *Agent) Stop(ctx context.Context) error {
@@ -151,6 +185,7 @@ func (a *Agent) run(ctx context.Context) {
 		registered    = session.registered
 		ready         = a.ready // first session ready
 		sessionq      chan sessionOperation
+		leaving       = a.leaving
 		subscriptions = map[string]context.CancelFunc{}
 	)
 
@@ -171,7 +206,21 @@ func (a *Agent) run(ctx context.Context) {
 		select {
 		case operation := <-sessionq:
 			operation.response <- operation.fn(session)
+		case <-leaving:
+			leaving = nil
+
+			// TODO(stevvooe): Signal to the manager that the node is leaving.
+
+			// when leaving we remove all assignments.
+			if err := a.worker.Assign(ctx, nil); err != nil {
+				log.G(ctx).WithError(err).Error("failed removing all assignments")
+			}
 		case msg := <-session.assignments:
+			// if we have left, accept no more assignments
+			if leaving == nil {
+				continue
+			}
+
 			switch msg.Type {
 			case api.AssignmentsMessage_COMPLETE:
 				// Need to assign secrets before tasks, because tasks might depend on new secrets