In this project, you are to:
a. Design and implement a readers/writers lock using semaphores that do not starve the
readers and do not starve the writers;
b. Write the main C program that uses Reader/Writer locks;
c. Come up with a set of input scenarios that shows the behavior of your nonstarving lock
compared to the starving lock.
The readers/writers problem is presented in section 31.5 of the textbook along with the
readers/writers lock that starves writers. There may be solutions published in articles over the
years – feel free to consult and cite them. It is not acceptable to use code that implements this
solution from the Internet or other sources other than your own work.
It is acceptable to use the
code from the textbook as your starter code, if useful.
This is an individual project.
The output of this project includes:
• A report (in PDF) that includes:
o Your name.
o A short description of the problem you address (hopefully not cut-andpasted from
this project but written in your own words).
o A description in plain English and pseudocode of your solution.
o An estimation of the time you spent working on the project.
This is likely to be a very short report – do not try to make it longer than it needs. But do
make it neater than your usual.
• A tar file that includes:
o A makefile for easy compilation. The target executable should be rwmain.
o A README file that describes how to run your project (arguments, etc).
o A C program, named readerwriter.c, that implements the nonstarving
o A C program, named main.c, that uses the locks and shows their functionality.
Note that the reading/writing parts of the code are only simulated: you do not
have to read or write a particular data structure; instead, you might want to
pretend to do it, and take some time such as:
int x=0, T; T =
for(i = 0; i < T; i++)
for(j = 0; j < T; j++)
This function is only meant to waste time for a variable amount of time. Feel free
to adjust this code as you see fit (or ignore all together if not useful in your
There are no required inputs to this program. You may use inputs if useful and
explain use in the readme file. Output messages useful for testing and debugging.
o An input file, named scenarios.txt, that proves that your lock:
▪ Is a correct readers/writers lock.
▪ Does not starve the writers.
▪ Does not starve the readers.
▪ Each scenario takes one line (as the traces file in last project) ▪ An
example and interpretation of this file is below:
This file contains two scenarios:
1. One in which one reader arrives first, then a writer, then four
more readers, another writer, then two more readers.
2. And the second in which two writers arrive first, then four
readers, one more writer, and one more reader.
▪ You want these scenarios to test corner cases that are relevant for the
point of your design: specifically, that writers will not starve. Thus, you
design these test scenarios to make it possible for writers to starve. You
do not need lots of readers/writers to make the case. You might want to
limit each scenario to 10–15 readers and writers at the very most.
To ease the task of grading, please name your files as requested and put all these files in the same
In addition, please hardcode the file name for scenarios.txt with the relative path (not the
absolute path) in your main.c code, e.g.:
FILE* ptr = fopen(“scenarios.txt “,”r”);
Suggestions on how to approach this project:
1) Understand the Readers/Writers problem and the solution provided:
a. Follow slides and video lecture on the topic (scheduled for Tuesday,
March 16 2021 lecture)
b. Check textbook (Chapter 31.5)
c. Look at the code (provided in the text but also on GitHub, linked from the web
version of the textbook).
d. (optional) Experiment with the code. If you use the GitHub version, you will
realize that it is more complicated than it needs to be because it is written to work
on both Mac and Linux systems. It thus obscures the API you will be using on
Linux machines. It is, however, a very good
2 opportunity to learn a bit more about programming. Alternatively, you can use the code
from the textbook and add what is needed (e.g., a main function to call the functions presented in
Figure 31.13) to test it and become comfortable with it.
2) Understand what the problem is with starving writers.
3) Design a solution to this problem (on “paper” first. Don’t code and hope you’ll fix your
understanding by debugging concurrency issues. Think first, then implement).
4) Ask questions:
a. During office hours (instructor’s or/and TA’s)
b. By email directly to us (cc instructor and both TAs).
5) Implement, debug, test on C4 lab machines, etc.
6) Make copies of your work. It is a stressful time, save your work with meaningful names
such that you reduce risks of overwriting your code, losing work due to disk crashes, etc.
7) Write report, edit, edit, edit, spell check, ….
8) Submit, of course.