Add queueing example model

examples/queueing/generator.py

@@ -0,0 +1,50 @@
+from pypdevs.DEVS import AtomicDEVS
+from job import Job
+import random
+
+# Define the state of the generator as a structured object
+class GeneratorState:
+    def __init__(self, gen_num):
+        # Current simulation time (statistics)
+        self.current_time = 0.0
+        # Remaining time until generation of new event
+        self.remaining = 0.0
+        # Counter on how many events to generate still
+        self.to_generate = gen_num
+
+class Generator(AtomicDEVS):
+    def __init__(self, gen_param, size_param, gen_num):
+        AtomicDEVS.__init__(self, "Generator")
+        # Output port for the event
+        self.out_event = self.addOutPort("out_event")
+        # Define the state
+        self.state = GeneratorState(gen_num)
+
+        # Parameters defining the generator's behaviour
+        self.gen_param = gen_param
+        self.size_param = size_param
+
+    def intTransition(self):
+        # Update simulation time
+        self.state.current_time += self.timeAdvance()
+        # Update number of generated events
+        self.state.to_generate -= 1
+        if self.state.to_generate == 0:
+            # Already generated enough events, so stop
+            self.state.remaining = float('inf')
+        else:
+            # Still have to generate events, so sample for new duration
+            self.state.remaining = random.expovariate(self.gen_param)
+        return self.state
+
+    def timeAdvance(self):
+        # Return remaining time; infinity when generated enough
+        return self.state.remaining
+
+    def outputFnc(self):
+        # Determine size of the event to generate
+        size = max(1, int(random.gauss(self.size_param, 5)))
+        # Calculate current time (note the addition!)
+        creation = self.state.current_time + self.state.remaining
+        # Output the new event on the output port
+        return {self.out_event: Job(size, creation)}