Index: errai-bus/src/main/java/org/jboss/errai/bus/server/MessageQueue.java
===================================================================
--- errai-bus/src/main/java/org/jboss/errai/bus/server/MessageQueue.java	(revision 1218)
+++ errai-bus/src/main/java/org/jboss/errai/bus/server/MessageQueue.java	(working copy)
@@ -21,6 +21,7 @@
 
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
 
 import static java.lang.System.currentTimeMillis;
@@ -46,7 +47,7 @@
     private int lastQueueSize = 0;
     private boolean throttleIncoming = false;
     private boolean queueRunning = true;
-    private volatile boolean pollActive = false;
+  //private volatile boolean pollActive = false;
 
     private boolean _windowPolling = false;
     private boolean windowPolling = false;
@@ -58,6 +59,8 @@
     private ServerMessageBus bus;
     private volatile TimedTask task;
 
+  private final Semaphore lock = new Semaphore(1, true);
+
     /**
      * Initializes the message queue with an initial size and a specified bus
      *
@@ -84,18 +87,25 @@
 
         checkSession();
         try {
-            MarshalledMessage m;
+      MarshalledMessage m = null;
+      
+      if( lock.tryAcquire(0, TimeUnit.SECONDS))
+      {
+        try
+        {
             if (wait) {
-                if (pollActive) {
-                    throw new RuntimeException("concurrent polling not allowed!");
-                }
-                pollActive = true;
                 m = queue.poll(45, TimeUnit.SECONDS);
-                pollActive = false;
+
             } else {
                 m = queue.poll();
             }
+        }
+        finally {
+          lock.release();          
+        }
 
+      }
+
             int payLoadSize = 0;
 
             Payload p = new Payload(m == null ? heartBeat : m);
@@ -104,6 +114,11 @@
                 windowPolling = true;
                 _windowPolling = false;
             } else if (windowPolling) {
+
+        try
+        {
+          if( lock.tryAcquire(0, TimeUnit.SECONDS))
+          {
                 while (!queue.isEmpty() && payLoadSize < MAXIMUM_PAYLOAD_SIZE
                         && !isWindowExceeded()) {
                     p.addMessage(queue.poll());
@@ -117,6 +132,12 @@
                         // just resume.
                     }
                 }
+          }
+        }
+        finally
+        {
+          lock.release();
+        }
 
                 if (!throttleIncoming && queue.size() > lastQueueSize) {
                     if (transmissionWindow < MAX_TRANSMISSION_WINDOW) {
@@ -282,7 +303,7 @@
      * @return true if the queue is stale
      */
     public boolean isStale() {
-        return !queueRunning || (!pollActive && (currentTimeMillis() - lastTransmission) > TIMEOUT);
+    return !queueRunning || (!isActive() && (currentTimeMillis() - lastTransmission) > TIMEOUT);
     }
 
     /**
@@ -291,7 +312,7 @@
      * @return true if the queue is actively polling
      */
     public boolean isActive() {
-        return pollActive;
+    return lock.availablePermits()==0;
     }
 
     /**