CPSC 420 -- Lab Exercise

Modifying the Program to Find the Maximum in the Queue

Modifying the Program to Model Two Servers in Series

When you are ready to implement this, make a new directory for the files (separate from the mm1) AND rename the mm1System class (and file) AND put your name in the documentation!!!!

1. First determine the state variables you should use and the best way to implement them in the program. After doing that,
   • Add the declarations to the program
   • Add the initializations (note that some initialization is done by the initialization routine and some by the constructor for an mm1System object)
2. We decided in class that there should be three events: an arrival to the system (an arrival at the first server) which is basically the same as the current arrival event, moving from the first to the second server (departing first server, arriving at second), and departing the system (departure from the second server). To add these events, do the following:
   • Think of a name for the new event and add that name to the eventType enumerated type (in the system declaration)
   • Add a declaration for a method to process that event
   • Recall that the updateState method is the one in charge of calling the correct routine to process an event. Add a case to the list in the switch statement to call the new method in the case that the event is the new event type.
   • Modify the current processArrival and processDeparture to use the correct server. You will also need to modify scheduleDeparture to schedule the departure from the correct server (you should add a parameter to send the server number).
   • Write a stub for the process routine for the new event. Have it do something simple like print a message and schedule a departure from the second server.
   • The printReport routine has a reference to the customerQ which should now be a subscripted variable, so for now subscript it with 0 (for the first server's queue).
   • Compile the program and run it to see if all seems well so far. Is there any way to tell at this point if all is well?
   • After all the bugs are out, go back and fill in the logic for the routine that processes the new event. Compile and run the program.
3. Now, we need to fix the statistical counters. Since we already have two queues and queue statistics (area under the Q(t) function) are kept track of by the Queue object, we don't need to worry about that.
   • We do need to now keep track of total delay in each queue, so change the totalDelay variable to a subscripted variable in the declaration and modify the code in the appropriate places (where is totalDelay updated, where is it used to calculate final statistics?).
   • We should also compute the number of customers who complete their delay in the two queues (the numbers will be almost the same for both queues but not quite). So the numCustomers variable needs to be subscripted. Make all necessary changes. (NOTE: in continueSim, use the number of customers who completed their delay at the second server -- numCustomers[1]).
   • There are now two different service times (still just one interarrival time), so the serviceTime randNum object needs to be subscripted. The means for the two mean service times should be read in in the initialization routine and the two objects initialized there. Then, the program must be modified in the place (and there is only one place!!!) where the random number generator is called to get a service time. The report printing routine prints out the service times so it must be modified.
   • Compile, run, and clean up any details I may have forgotten to point out to you. (NOTE: For now leave the stopping condition to be when a certain number of customers complete their delay at the second server. The book says to stop after exactly 1000 minutes of simulated time. We'll talk about stopping conditions Thursday.)