#!/usr/bin/env python

# MachRep1.py

# Introductory SimPy example:  Two machines, which sometimes break down.
# Up time is exponentially distributed with mean 1.0, and repair time is
# exponentially distributed with mean 0.5.  There are two repairpersons,
# so the two machines can be repaired simultaneously if they are down
# at the same time.

# Output is long-run proportion of up time.  Should get value of about
# 0.66.

import SimPy.Simulation  # required
import random 

class G:  # global variables
   Rnd = random.Random(12345)

class MachineClass(SimPy.Simulation.Process):
   UpRate = 1/1.0  # reciprocal of mean up time
   RepairRate = 1/0.5  # reciprocal of mean repair time
   TotalUpTime = 0.0  # total up time for all machines
   NextID = 0  # next available ID number for MachineClass objects
   def __init__(self):  # required constructor
      SimPy.Simulation.Process.__init__(self)  # must call parent constructor
      # instance variables
      self.StartUpTime = 0.0  # time the current up period started
      self.ID = MachineClass.NextID   # ID for this MachineClass object
      MachineClass.NextID += 1
   def Run(self):  # required constructor
      while 1:
         # record current time, now(), so can see how long machine is up
         self.StartUpTime = SimPy.Simulation.now()  
         # hold for exponentially distributed up time
         UpTime = G.Rnd.expovariate(MachineClass.UpRate)
         yield SimPy.Simulation.hold,self,UpTime  # simulate UpTime 
         # update up time total
         MachineClass.TotalUpTime += SimPy.Simulation.now() - self.StartUpTime
         RepairTime = G.Rnd.expovariate(MachineClass.RepairRate)
         # hold for exponentially distributed repair time
         yield SimPy.Simulation.hold,self,RepairTime

def main():
   SimPy.Simulation.initialize()  # required 
   # set up the two machine threads
   for I in range(2):
      # create a MachineClass object
      M = MachineClass()
      # register thread M, executing M's Run() method,
      SimPy.Simulation.activate(M,M.Run())  # required
   # run until simulated time 10000
   MaxSimtime = 10000.0
   SimPy.Simulation.simulate(until=MaxSimtime)  # required
   print "the percentage of up time was", \
      MachineClass.TotalUpTime/(2*MaxSimtime)

if __name__ == '__main__':  main()