CSCE 3600: Systems Programming
CSCE 3600: Systems Programming
Minor Assignment 4 – Threads, Mutexes, and Condition Variables
Due: 11:59 PM on Thursday, April 8, 2021
PROGRAM DESCRIPTION:
In this assignment, you will be given a functioning program, called minor4.c, that
simply reads user input digits (a string, separated into individual characters) and
compares each pair and displays the result of the comparison two digits at time using
the producer-consumer paradigm. The single producer thread reads user input
characters in pairs, makes sure they are single digits and places them into a pair of
buffers (A and B) while two consumer threads read the pairs of values and compares
them displaying the result of the comparison to the screen. To complicate matters, each
pair of digits (i.e., character) is read and compared by exactly one consumer thread. A
shared variable, called shared_count, keeps track of the number of items in the
shared buffer.
While this program does work (thanks to the mutex locks and unlocks already provided),
it is unfortunately very inefficient. To see just how inefficient this program is, compile the
original minor4.c program (using the pthread library) and execute the program. You
should type in some keys and see them echoed back on the screen in their correct
order. To see the inefficiency, though, run the top command from another shell (don’t
just run the minor4.c program in the background and then run top, but actually open
up another shell/window). Then check out the %CPU column in the top command and
you should see your original minor4.c program using up a significant percentage of
the CPU, which is not good.
Your goal for this assignment is to modify this program to use condition variables that
will drastically reduce its CPU percentage usage. Here are the details:
-
You will modify the original minor4.c file to add two condition variables, but not
change the “spirit” of the program other than necessary changes that are needed
for how conditional variables work, including handling of “spurious wakeup”
discussed in class.
-
You will add two global pthread condition variables – one to handle when the
shared buffer is full (and therefore, nothing else can be added to the buffer until a
key is removed from the buffer) and one to handle when the shared buffer is
empty (and therefore, nothing can be read/echoed back to the screen until a key
is added to the buffer).
-
In the main function, you will initialize and destroy both of the condition variables.
-
You will modify the code in the producer function to wait on and signal the
appropriate condition variable(s) based on what is happening with the shared
variables (i.e., the shared buffer and shared counter) Note that this will require some small changes in logic to accomplish, but you should not change the lines
that work with the prod_index variable.
-
You will modify the code in the consumer function to wait on and signal the
appropriate condition variable(s) based on what is happening with the shared
variables (i.e., the shared buffer and shared counter). Note that this will require
some small changes in logic to accomplish, but you should not change the lines
that work with the cons_index variable.
Be sure to run your solution along with the top command to verify that the program is
more efficient (i.e., does not use nearly as much percentage of the CPU). It is required
that you implement and utilize the condition variables effectively in a manner that
significantly reduces the CPU utilization of this program and not gain the reduction in
another way. Note that the grading rubric requires that the condition variables be
implemented “logically correct”, which includes accounting for “spurious wakeup”, not
just reducing the CPU utilization.
DETAILED ASSIGNMENT