OperatorPreemptive corrected

dream/simulation/OperatorPreemptive.py

@@ -46,19 +46,22 @@ class OperatorPreemptive(Operator):
     def checkIfResourceIsAvailable(self,callerObject=None): 
         activeResource= self.getResource()
         activeResourceQueue = activeResource.getResourceQueue()
-        try:
-            # read the station operated by the operator
+        # find out which station is requesting the operator?
+        thecaller=callerObject
+        # if the operator is occupied return True
+        if len(activeResourceQueue)==0:
+            return True
+        # read the station currently operated by the operator
         victim=activeResourceQueue[0]
         # read its activeQ
         victimQueue=victim.getActiveObjectQueue()
-            # find out which station is requesting the operator?
-            thecaller=callerObject
+        # if the callerObject is None then return False as the operator is occupied
+        if thecaller==None:
+            return False
         thecallerQueue=thecaller.getActiveObjectQueue()
-            
-            #if the receiver is not empty
-            if len(victimQueue)>0:
-                # and the caller is not empty
-                if len(thecallerQueue)>0:
+        #if the receiver is not empty and the caller is not empty
+        if len(victimQueue)>0 and len(theCallerQueue):
+            try:
                 #if the  Entity to be forwarded to the station currently processed by the operator is critical
                 if thecallerQueue[0].isCritical:
                     #if the receiver does not hold an Entity that is also critical
@@ -68,7 +71,7 @@ class OperatorPreemptive(Operator):
                         victim.preempt()
                         victim.timeLastEntityEnded=now()     #required to count blockage correctly in the preemptied station
                         return True
-        # if the operator is not occupied, or if the caller is None then perform the default behaviour
+            # if the entity has no isCritical property then ran the default behaviour
             except:
                 pass
         return len(self.Res.activeQ)<self.capacity