[IMPROVED] Consumer cleanup monitoring and FIX for datarace (#4536)

Signed-off-by: Derek Collison <derek@nats.io>

server/consumer.go

@@ -1544,19 +1544,32 @@ func (o *consumer) deleteNotActive() {
 	// If we do forward a proposal to delete ourselves to the metacontroller leader.
 	if !isDirect && s.JetStreamIsClustered() {
 		js.mu.RLock()
+		var (
+			cca         consumerAssignment
+			meta        RaftNode
+			removeEntry []byte
+		)
 		ca, cc := js.consumerAssignment(acc, stream, name), js.cluster
-		js.mu.RUnlock()
-
 		if ca != nil && cc != nil {
-			cca := *ca
+			meta = cc.meta
+			cca = *ca
 			cca.Reply = _EMPTY_
-			meta, removeEntry := cc.meta, encodeDeleteConsumerAssignment(&cca)
+			removeEntry = encodeDeleteConsumerAssignment(&cca)
 			meta.ForwardProposal(removeEntry)
+		}
+		js.mu.RUnlock()
 
+		if ca != nil && cc != nil {
 			// Check to make sure we went away.
 			// Don't think this needs to be a monitored go routine.
 			go func() {
-				ticker := time.NewTicker(10 * time.Second)
+				const (
+					startInterval = 5 * time.Second
+					maxInterval   = 5 * time.Minute
+				)
+				jitter := time.Duration(rand.Int63n(int64(startInterval)))
+				interval := startInterval + jitter
+				ticker := time.NewTicker(interval)
 				defer ticker.Stop()
 				for range ticker.C {
 					js.mu.RLock()
@@ -1566,9 +1579,14 @@ func (o *consumer) deleteNotActive() {
 					if nca != nil && nca == ca {
 						s.Warnf("Consumer assignment for '%s > %s > %s' not cleaned up, retrying", acc, stream, name)
 						meta.ForwardProposal(removeEntry)
-					} else {
-						return
+						if interval < maxInterval {
+							interval *= 2
+							ticker.Reset(interval)
+						}
+						continue
 					}
+					// We saw that consumer has been removed, all done.
+					return
 				}
 			}()
 		}