Race condition in pubsub #469 (#471)

* Race condition in pubsub #469

* use allFinished

* improve cancellation handling

libp2p/protocols/pubsub/pubsub.nim

@@ -169,15 +169,22 @@ proc getOrCreatePeer*(
 proc handleData*(p: PubSub, topic: string, data: seq[byte]): Future[void] {.async.} =
   if topic notin p.topics: return # Not subscribed
 
-  for h in p.topics[topic].handler:
-    trace "triggering handler", topicID = topic
+  # gather all futures without yielding to scheduler
+  var futs = p.topics[topic].handler.mapIt(it(topic, data))
+  
   try:
-      await h(topic, data)
-    except CancelledError as exc:
-      raise exc
-    except CatchableError as exc:
-      # Handlers should never raise exceptions
-      warn "Error in topic handler", msg = exc.msg
+    futs = await allFinished(futs)
+  except CancelledError:
+    # propagate cancellation
+    for fut in futs:
+      if not(fut.finished):
+        fut.cancel()
+  
+  # check for errors in futures
+  for fut in futs:
+    if fut.failed:
+      let err = fut.readError()
+      warn "Error in topic handler", msg = err.msg
 
 method handleConn*(p: PubSub,
                    conn: Connection,