Add queueing example model

examples/queueing/collector.py

@@ -0,0 +1,29 @@
+from pypdevs.DEVS import AtomicDEVS
+
+# Define the state of the collector as a structured object
+class CollectorState(object):
+    def __init__(self):
+        # Contains received events and simulation time
+        self.events = []
+        self.current_time = 0.0
+
+class Collector(AtomicDEVS):
+    def __init__(self):
+        AtomicDEVS.__init__(self, "Collector")
+        self.state = CollectorState()
+        # Has only one input port
+        self.in_event = self.addInPort("in_event")
+
+    def extTransition(self, inputs):
+        # Update simulation time
+        self.state.current_time += self.elapsed
+        # Calculate time in queue
+        evt = inputs[self.in_event]
+        time = self.state.current_time - evt.creation_time - evt.processing_time
+        inputs[self.in_event].queueing_time = max(0.0, time)
+        # Add incoming event to received events
+        self.state.events.append(inputs[self.in_event])
+        return self.state
+
+    # Don't define anything else, as we only store events.
+    # Collector has no behaviour of its own.