The program for this assignment, and everything else except the README file, is due at 9 P.M. on Wednesday, April 7th, 2004. As usual, the README file is due at midnight the same day (i.e., the moment that Thursday starts). Refer to the homework policies page for general homework guidelines.
The primary purpose of this assignment is to familiarize you with C++ templates. In fact, once you have finished converting your list class to support templates, you will discover that there is relatively little else to be done.
NOTE: the templated list class you develop in this assignment MUST be based on your solution to assignment 7. It will also be central to assignment 9. A correct solution to this assignment will NOT be distributed to the class.
Not far from Deep Glen Polytechnic University is Storm's Juice Bar. On any typical night, it is packed with rowdy DGP students who are assiduously avoiding their studies.
Wesley Storm, the owner and bartender, is a very busy man. Known as "Wes the Bar Monkey" because of his long arms and seeming ability to mix four drinks at once, he works all day, every day, to ensure that his customers are happy. Since Storm's is a fairly large place, he also employs several students as table servers. If a customer is seated at the bar, Wes serves drinks directly, but the servers carry drinks to customers at the tables. Servers have priority over individual customers. When a server arrives, Wes stops mixing drinks for individual customers, and doesn't return to that task until there are no table servers waiting.
Recently, Wes has become concerned about the quality of the service he is providing. It seems to him that he is slowing down, and he worries that he will lose customers if they find themselves waiting too long for their next drink.
To address the problem, Wes has asked you and a friend, Janet McMudd, to develop a simulation of the bar's operation. His hope is that by experimenting with the simulation parameters, he will be able to find out how long he can continue to work alone before his customers become unhappy. Janet wrote a lot of useful code, but unfortunately she took a break and headed over to Storm's, where she is currently passed out under a table, the victim of severe sleep deprivation. Your job is to finish the simulation so that Wes will fulfill his promise of free drinks for the remainder of your college career.
The bar simulation will be done using a technique called "discrete-event simulation". This method is used for systems where the activity can be broken down into individual events, such as bank customers using an ATM. (The other type of simulation is "continuous-system simulation," used for things where the behavior is continuous, such as spacecraft flight.) A typical discrete-event simulation is based on one or more queues, in which the events are stored until it is time to process them.
To simplify the job of doing the simulation, Janet's design concentrates on the bartender. The program assumes that individual drinkers and table servers arrive at the bar and place orders at random times. As is common in simulations (and in real life), the arrival pattern is exponentially distributed (more accurately, the time between arrivals is exponentially distributed). Don't worry if you don't know what that means, because Janet already finished that part of the code.
The main part of the simulation runs from two queues: one containing individual drinkers, the other containing table servers. The queues are sorted by arrival time. The simulation merely needs to choose a customer from one queue or the other, provide the appropriate service, and record useful statistics about the customer. For simplicity, the finite population of customers and servers is modeled as an infinite population; this saves the trouble of simulating the time spent drinking and wandering around between tables.
Since your friend Janet is a big C++ fan, she decided to implement the
queues using an existing linked-list class. However, since the
simulation needs to store two different data types
(Drinker and TableServer) in the two queues,
she decided to convert the list into a templated class so she could
use the same code for both queues. She didn't finish the conversion,
so you are stuck with that job.
As mentioned above, the templated list class is used as a queue. This is the only data structure you need to implement. (Properly speaking, it's used as three-fourths of a deque: your class must support pushing and popping at the head, but only pushing at the tail. That means that your singly linked list from assignment 7 is sufficient.)
The program also uses several other structures:
BarRequester is a base class for Drinker and
TableServer, which represent individual customers and
table servers, respectively. There is also a
SimulationTime class that keeps track of the simulated
time during a run. Janet finished writing and debugging those classes,
so you don't have to worry about them (although they are worth
studying, since Janet is known as a pretty talented coder).
To complete this assignment, you must do the following tasks:
barMonkey).
The most difficult part of the assignment is the last item: template conversion. Although superficially easy, this task is often very painful for newcomers to C++. The syntax is messy, the requirements often don't make sense, and (at least with g++) the error messages are monumentally unhelpful. Worse, some of your compile errors won't show up until you actually use the templates, so piecemeal error-finding techniques won't work.
The single biggest thing you can do to ease your task is to ask for help. It turns out that there is almost nothing to be learned from trying to solve template compilation errors on your own. It's all a bunch of tricks, with no logic to them, and the best way to learn them is to have somebody else show them to you. So if you find yourself puzzling over a compilation error for more than 5 minutes, we strongly suggest that you find somebody to help you with it. You will save yourself an astounding amount of time. (Prof. Kuenning likes to tell about the time he got rid of 187 template-related compilation errors in 3 minutes flat!)
You must create or modify the following files:
assign_08.cc
Makefile
list.hh
List) and its templated iterator,
ListIterator.
Note that both classes must be defined
by this file, either by placing both definitions in the
file, or by having it #include whatever
file(s) contain the remaining definitions.
(Note: ListIterator is not used in
this assignment. However, you will need it for the next
assignment, so it's better to convert it to use templates
now if at all possible.)
*.hh
*.cc
*.icc
In addition, you will need to download the following files that are part of the program, but you may not modify them:
barrequester.hh
BarRequester
class and its derivatives: Drinker and
TableServer. It also defines the
TimeStatistics class for collecting
statistical information.
barrequester.cc
BarRequester and its related classes.
mtwist.c, mtwist.h, and
mtwist.3
nroff -man
mtwist.3 | less -s. For CS70 purposes, you can
treat the random-number generator as an opaque package.
randistrs.c, randistrs.h, and
randistrs.3
simulationconstants.hh
simulationtime.hh
SimulationTime
class.
simulationtime.cc
SimulationTime class.
In assign_08.cc, you must provide the main simulation
loop, in the barMonkey function. Since this is not a
class in simulation, that file contains pseudocode to help guide you
in writing the loop.
The places where you need to provide code are marked by "ADD STUFF" comments.
Since assign_08.cc is provided to you, you must maintain
stylistic consistency in that file. However, you are not required to
use any specific coding style in the
other files that you create. Since you are creating them from scratch, any
good style is acceptable. In particular, you do not have to
match the style of assign_08.cc in those files.
As usual,
you must check out the provided files by using "cs70checkout
hw08".
When you have a working solution, you must submit your files with
cs70submit. If you create any new files, you need to
tell the submission system about them by mentioning them once on a
cs70submit command line.
For convenience, we have provided dummy versions of
README, Makefile, and list.hh
so that they will be sure to get submitted.
Testing is your responsibility. We will not provide exact test cases for you. You should test your program a number of times, under different conditions.
In its default condition, the program is nondeterministic (i.e., two successive runs may produce different results). To make testing easier, the program accepts a switch that makes it deterministic. If you use "-S all n", where n is an integer, the random seed will be set to that value. (More accurately, n will be used to set several random seeds, since the program uses four different pseudorandom number generators, or PRNGS.) Specifying the random seed will allow you to control the program's behavior so that you can reproduce bugs.
You will also find it instructive to run the program with various
values for the
-D, -M, -P, -r,
-s, and -T switches.
Judicious reading of the comments, together with experimentation, will
reveal the purpose of these switches and how they interact.
We will not limit ourselves to running only simple test cases. You can expect that we will run stress tests in an attempt to break your program.
To help you be sure you have written correct code, we have provided a sample of the output from a simulation run with the switches "-S all 1".
icc Files
By default, emacs doesn't know that icc files contain C++
code. There are three ways to tell emacs to use C++ mode:
ESC x c++-mode RET" each time you visit
the file. Obviously, this is a pain.
// ;-*-C++-*-" as the first line
of the file. Emacs will recognize the line and automatically
switch to C++ mode. This is less of a pain, but you still
have to do it to every file.
.emacs" file in
your home directory. (If you don't have a
".emacs" file, create one containing this line):
(setq auto-mode-alist (append '(("\\.icc$" . c++-mode)) auto-mode-alist))
The line must be inserted exactly as given above,
including the double backslash, the parentheses, and the funny
single quote.
As usual there are some tricky parts to this assignment. Some of them are:
peekHead() function in your list class.
typename" in front of the type reference
it is complaining about. The reasons for this message are
subtle, so it is easier to just know a recipe for curing
it.
assign_08.cc.
.icc file directly. You
must have some sort of .cc file (such as
assign_08.cc or a little test program) that includes a
.hh file, which in turn includes the
.icc file.
#include to include
.cc files into any other file.
© 2004, Geoff Kuenning
This page is maintained by Geoff Kuenning.