Back to the original flow-visibility rules

os2.rkt

@@ -144,6 +144,14 @@
   (and (roles-intersect? (topic-role left) (topic-role right))
        (mgu-canonical (freshen (topic-pattern left)) (freshen (topic-pattern right)))))
 
+;; True iff the flow between remote-topic and local-topic should be
+;; visible to the local peer. This is the case when either local-topic
+;; is virtual (in which case everything is seen) or otherwise if
+;; remote-topic is also not virtual.
+(define (flow-visible? local-topic remote-topic)
+  (or (topic-virtual? local-topic)
+      (not (topic-virtual? remote-topic))))
+
 ;;---------------------------------------------------------------------------
 
 ;; QuasiQueue<X>
@@ -216,16 +224,20 @@
 		       #:when flow-pattern)
 		    (define inbound-flow (refine-topic matching-topic flow-pattern))
 		    (define outbound-flow (refine-topic topic flow-pattern))
-		    (let* ((state (run-trapk state
-					     pid
-					     (handlers-presence hs)
-					     new-eid
-					     inbound-flow))
-			   (state (run-trapk state
-					     matching-pid
-					     (handlers-presence (endpoint-handlers e))
-					     matching-eid
-					     outbound-flow)))
+		    (let* ((state (if (flow-visible? topic inbound-flow)
+				      (run-trapk state
+						 pid
+						 (handlers-presence hs)
+						 new-eid
+						 inbound-flow)
+				      state))
+			   (state (if (flow-visible? matching-topic outbound-flow)
+				      (run-trapk state
+						 matching-pid
+						 (handlers-presence (endpoint-handlers e))
+						 matching-eid
+						 outbound-flow)
+				      state)))
 		      state))
 	       [processes (hash-set (vm-processes state)
 				    pid