CSCE 3600 Threads, Mutexes, and Condition Variables

PROGRAM DESCRIPTION:

In this assignment, you will be given a functioning program, called minor3.c, that simply reads user input keys (a string, separated into individual characters) and echoes them back to the screen one character at a time using the producer-consumer paradigm. The single producer thread reads user input keys and adds them to the shared buffer while two consumer threads read the added keys from the buffer and echo them back to the screen. To complicate matters, each key (i.e., character) is read and echoed 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 minor3.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 minor3.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 minor3.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 minor3.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.