42 lines
2.3 KiB
ReStructuredText
42 lines
2.3 KiB
ReStructuredText
..
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Copyright 2014 Modelling, Simulation and Design Lab (MSDL) at
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McGill University and the University of Antwerp (http://msdl.cs.mcgill.ca/)
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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Listening to realtime simulation
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================================
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During realtime simulation, there frequently exists the need to listen to specific ports, monitoring the events passing over them. In PythonPDEVS, it is possible to register a function that is invoked for each event passing over that port. This is called a *listener* in PythonPDEVS.
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Example model
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-------------
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We can simply reuse the traffic light model from the previous section on realtime simulation (:download:`trafficLightModel.py <trafficLightModel.py>`). All that needs to be changed now, is adding a listener on an output port of a *coupled* DEVS model. First and foremost, therefore, we must put our traffic light in a container::
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class TrafficLightSystem(CoupledDEVS):
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def __init__(self):
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CoupledDEVS.__init__(self, "System")
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self.light = self.addSubModel(TrafficLight("Light"))
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self.observed = self.addOutPort(name="observed")
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In the experiment file, it is then possible to register a listener on this port as follows (:download:`injection.py <injection.py>`)::
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def my_function(event):
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print("Observed the following event: " + str(event))
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sim.setListenPorts(model.observed, my_function)
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Since this function is invoked with the complete bag, the received event will contain a list of events, exactly as how it would be invoked in the external transition function.
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.. note:: Listeners are only supported on output ports of Coupled DEVS models. This is because the listeners are invoked upon event routing, for which the source port is not checked.
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