How to split up dependent events in SimPy

Question

I want to implement a discrete-event maintenance scheduling simulation in which some maintenance activities must happen whenever another one happens.

For example, if walls are repainted every 5 years, and dry-lining is replaced every 14 years, then walls must be repainted whenever the dry-lining is replaced and the clock restarted.

yr 5:  paint walls
yr 10: paint walls
yr 14: replace dry-lining
yr 14: paint walls
yr 19: paint walls
...

I'm not sure whether I should implement each activity as a process which refers to the dependent process, or if "wall maintenance" should be a process with the logic handled internally, or some other way of.

The code I have has each activity as a process with the dependent process stored as an attribute but I feel like I'm probably missing the correct way of doing this as I'm seeing events happen twice in the same year.

Answer 1

This is the approach I took in the end:

import simpy
from simpy.events import Interrupt


class Construction(object):

    def __init__(self, name, components):
        self.name = name
        self.components = components
        self.link_components()

    def link_components(self):
        """Link each component to the next outermost component      
        """
        for i, component in enumerate(self.components):
            try:
                component.dependent = self.components[i+1]
            except IndexError:
                component.dependent = None                

class Component(object):

    def __init__(self, env, name, lifespan):
        """Represents a component used in a construction.

        """
        self.env = env
        self.name = name
        self.lifespan = lifespan    
        self.action = env.process(self.run())

    def run(self):
        while True:
            try:
                yield self.env.timeout(self.lifespan)
                self.replace()
            except Interrupt:  # don't replace
                pass

    def replace(self):
        print "yr %d:  replace %s" % (env.now, self.name)
        if self.dependent:
            self.dependent.action.interrupt()  # stop the dependent process
            self.dependent.replace()  # replace the dependent component


env = simpy.Environment()
components = [Component(env, 'structure', 60),
              Component(env, 'dry-lining', 14),
              Component(env, 'paint', 5)]
wall = Construction('wall', components)
env.run(until=65)