[manager/dispatcher] Synchronize Dispatcher.Stop() with incoming rpcs.

Signed-off-by: Anshul Pundir <anshul.pundir@docker.com>
(cherry picked from commit 0b2778a)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

manager/dispatcher/dispatcher.go

@@ -125,8 +125,12 @@ type clusterUpdate struct {
 
 // Dispatcher is responsible for dispatching tasks and tracking agent health.
 type Dispatcher struct {
-	mu                   sync.Mutex
-	wg                   sync.WaitGroup
+	// mu is a lock to provide  mutually exclusive access to dispatcher fields
+	// e.g. lastSeenManagers, networkBootstrapKeys, lastSeenRootCert etc.
+	mu sync.Mutex
+	// shutdownWait is used by stop() to wait for existing operations to finish.
+	shutdownWait sync.WaitGroup
+
 	nodes                *nodeStore
 	store                *store.MemoryStore
 	lastSeenManagers     []*api.WeightedPeer
@@ -249,8 +253,11 @@ func (d *Dispatcher) Run(ctx context.Context) error {
 	defer cancel()
 	d.ctx, d.cancel = context.WithCancel(ctx)
 	ctx = d.ctx
-	d.wg.Add(1)
-	defer d.wg.Done()
+
+	// If Stop() is called, it should wait
+	// for Run() to complete.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
 	d.mu.Unlock()
 
 	publishManagers := func(peers []*api.Peer) {
@@ -313,11 +320,14 @@ func (d *Dispatcher) Stop() error {
 		return errors.New("dispatcher is already stopped")
 	}
 
-	log := log.G(d.ctx).WithField("method", "(*Dispatcher).Stop")
-	log.Info("dispatcher stopping")
+	// Cancel dispatcher context.
+	// This should also close the the streams in Tasks(), Assignments().
 	d.cancel()
 	d.mu.Unlock()
 
+	// Wait for the RPCs that are in-progress to finish.
+	d.shutdownWait.Wait()
+
 	d.nodes.Clean()
 
 	d.processUpdatesLock.Lock()
@@ -328,9 +338,6 @@ func (d *Dispatcher) Stop() error {
 	d.processUpdatesLock.Unlock()
 
 	d.clusterUpdateQueue.Close()
-
-	d.wg.Wait()
-
 	return nil
 }
 
@@ -478,13 +485,13 @@ func nodeIPFromContext(ctx context.Context) (string, error) {
 
 // register is used for registration of node with particular dispatcher.
 func (d *Dispatcher) register(ctx context.Context, nodeID string, description *api.NodeDescription) (string, error) {
-	logLocal := log.G(ctx).WithField("method", "(*Dispatcher).register")
-	// prevent register until we're ready to accept it
 	dctx, err := d.isRunningLocked()
 	if err != nil {
 		return "", err
 	}
 
+	logLocal := log.G(ctx).WithField("method", "(*Dispatcher).register")
+
 	if err := d.nodes.CheckRateLimit(nodeID); err != nil {
 		return "", err
 	}
@@ -532,6 +539,21 @@ func (d *Dispatcher) register(ctx context.Context, nodeID string, description *a
 // UpdateTaskStatus updates status of task. Node should send such updates
 // on every status change of its tasks.
 func (d *Dispatcher) UpdateTaskStatus(ctx context.Context, r *api.UpdateTaskStatusRequest) (*api.UpdateTaskStatusResponse, error) {
+	// shutdownWait.Add() followed by isRunning() to ensures that
+	// if this rpc sees the dispatcher running,
+	// it will already have called Add() on the shutdownWait wait,
+	// which ensures that Stop() will wait for this rpc to complete.
+	// Note that Stop() first does Dispatcher.ctx.cancel() followed by
+	// shutdownWait.Wait() to make sure new rpc's don't start before waiting
+	// for existing ones to finish.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
+
+	dctx, err := d.isRunningLocked()
+	if err != nil {
+		return nil, err
+	}
+
 	nodeInfo, err := ca.RemoteNode(ctx)
 	if err != nil {
 		return nil, err
@@ -547,11 +569,6 @@ func (d *Dispatcher) UpdateTaskStatus(ctx context.Context, r *api.UpdateTaskStat
 	}
 	log := log.G(ctx).WithFields(fields)
 
-	dctx, err := d.isRunningLocked()
-	if err != nil {
-		return nil, err
-	}
-
 	if _, err := d.nodes.GetWithSession(nodeID, r.SessionID); err != nil {
 		return nil, err
 	}
@@ -723,16 +740,26 @@ func (d *Dispatcher) processUpdates(ctx context.Context) {
 // of tasks which should be run on node, if task is not present in that list,
 // it should be terminated.
 func (d *Dispatcher) Tasks(r *api.TasksRequest, stream api.Dispatcher_TasksServer) error {
-	nodeInfo, err := ca.RemoteNode(stream.Context())
+	// shutdownWait.Add() followed by isRunning() to ensures that
+	// if this rpc sees the dispatcher running,
+	// it will already have called Add() on the shutdownWait wait,
+	// which ensures that Stop() will wait for this rpc to complete.
+	// Note that Stop() first does Dispatcher.ctx.cancel() followed by
+	// shutdownWait.Wait() to make sure new rpc's don't start before waiting
+	// for existing ones to finish.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
+
+	dctx, err := d.isRunningLocked()
 	if err != nil {
 		return err
 	}
-	nodeID := nodeInfo.NodeID
 
-	dctx, err := d.isRunningLocked()
+	nodeInfo, err := ca.RemoteNode(stream.Context())
 	if err != nil {
 		return err
 	}
+	nodeID := nodeInfo.NodeID
 
 	fields := logrus.Fields{
 		"node.id":      nodeID,
@@ -846,16 +873,26 @@ func (d *Dispatcher) Tasks(r *api.TasksRequest, stream api.Dispatcher_TasksServe
 // Assignments is a stream of assignments for a node. Each message contains
 // either full list of tasks and secrets for the node, or an incremental update.
 func (d *Dispatcher) Assignments(r *api.AssignmentsRequest, stream api.Dispatcher_AssignmentsServer) error {
-	nodeInfo, err := ca.RemoteNode(stream.Context())
+	// shutdownWait.Add() followed by isRunning() to ensures that
+	// if this rpc sees the dispatcher running,
+	// it will already have called Add() on the shutdownWait wait,
+	// which ensures that Stop() will wait for this rpc to complete.
+	// Note that Stop() first does Dispatcher.ctx.cancel() followed by
+	// shutdownWait.Wait() to make sure new rpc's don't start before waiting
+	// for existing ones to finish.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
+
+	dctx, err := d.isRunningLocked()
 	if err != nil {
 		return err
 	}
-	nodeID := nodeInfo.NodeID
 
-	dctx, err := d.isRunningLocked()
+	nodeInfo, err := ca.RemoteNode(stream.Context())
 	if err != nil {
 		return err
 	}
+	nodeID := nodeInfo.NodeID
 
 	fields := logrus.Fields{
 		"node.id":      nodeID,
@@ -1103,6 +1140,24 @@ func (d *Dispatcher) markNodeNotReady(id string, state api.NodeStatus_State, mes
 // Node should send new heartbeat earlier than now + TTL, otherwise it will
 // be deregistered from dispatcher and its status will be updated to NodeStatus_DOWN
 func (d *Dispatcher) Heartbeat(ctx context.Context, r *api.HeartbeatRequest) (*api.HeartbeatResponse, error) {
+	// shutdownWait.Add() followed by isRunning() to ensures that
+	// if this rpc sees the dispatcher running,
+	// it will already have called Add() on the shutdownWait wait,
+	// which ensures that Stop() will wait for this rpc to complete.
+	// Note that Stop() first does Dispatcher.ctx.cancel() followed by
+	// shutdownWait.Wait() to make sure new rpc's don't start before waiting
+	// for existing ones to finish.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
+
+	// isRunningLocked() is not needed since its OK if
+	// the dispatcher context is cancelled while this call is in progress
+	// since Stop() which cancels the dispatcher context will wait for
+	// Heartbeat() to complete.
+	if !d.isRunning() {
+		return nil, status.Errorf(codes.Aborted, "dispatcher is stopped")
+	}
+
 	nodeInfo, err := ca.RemoteNode(ctx)
 	if err != nil {
 		return nil, err
@@ -1137,17 +1192,27 @@ func (d *Dispatcher) getRootCACert() []byte {
 // a special boolean field Disconnect which if true indicates that node should
 // reconnect to another Manager immediately.
 func (d *Dispatcher) Session(r *api.SessionRequest, stream api.Dispatcher_SessionServer) error {
-	ctx := stream.Context()
-	nodeInfo, err := ca.RemoteNode(ctx)
+	// shutdownWait.Add() followed by isRunning() to ensures that
+	// if this rpc sees the dispatcher running,
+	// it will already have called Add() on the shutdownWait wait,
+	// which ensures that Stop() will wait for this rpc to complete.
+	// Note that Stop() first does Dispatcher.ctx.cancel() followed by
+	// shutdownWait.Wait() to make sure new rpc's don't start before waiting
+	// for existing ones to finish.
+	d.shutdownWait.Add(1)
+	defer d.shutdownWait.Done()
+
+	dctx, err := d.isRunningLocked()
 	if err != nil {
 		return err
 	}
-	nodeID := nodeInfo.NodeID
 
-	dctx, err := d.isRunningLocked()
+	ctx := stream.Context()
+	nodeInfo, err := ca.RemoteNode(ctx)
 	if err != nil {
 		return err
 	}
+	nodeID := nodeInfo.NodeID
 
 	var sessionID string
 	if _, err := d.nodes.GetWithSession(nodeID, r.SessionID); err != nil {