Description

Total 1 point
Objective
At the end of this mini-lab, you will be able to:
• Gain hands-on experience in multi-thread programming using Pthread.
• Identify a typical adding race condition and address it using condition variables or semaphores.
Instructions
In this mini-lab, you will identify and rectify a typical race condition scenario using condition variables or semaphores.
1. Complete multithread addition (TODO1 & TODO2) in lab4-multithread.c, compile and run the file.
Expected behavior: The counter variable is updated in the count_up function. Ideally, the counter value should end up with 4e6, as each of the 4 threads increases the counter by 1e6 times.
Note: For compilation of a C program that includes the pthread.h header, use the option
-pthread after gcc. e.g., gcc lab4-multithread.c -pthread -o lab4-multithread.
2. Address this race condition by completing TODO3 using either conditional variable or semaphore, and re-executing the program.
3. If implemented correctly, the final output should match the expected value.
Submission
(1 pt) Complete all the TODO sections and submit your code as lab4-pthread_<your_student_id>.c.
1
Appendix
// file: lab4-pthread.c
#include <stdio.h>
#include <pthread.h>
#define NUM_THREADS 4
#define NUM_ITERATIONS 1000000
int counter = 0;
// TODO3: define global variables (~1 line)
void *count_up(void *arg) { for (int i = 0; i < NUM_ITERATIONS; i++) {
// TODO3: Protect the counter increment operation to prevent race conditions
counter++;
}
return NULL;
}
int main(int argc, char *argv[]) { pthread_t threads[NUM_THREADS];
// TODO3: init condition variables/semphore (~1 line)
for (int i = 0; i < NUM_THREADS; i++) {
// TODO1: Create multiple threads to execute count_up (~1 line)
}
for (int i = 0; i < NUM_THREADS; i++) {
// TODO2: wait all the threads to finish running (~1 line)
}
// TODO3: free condition variables/semphore (~1 line)
printf(“Final counter value: %d “, counter);
printf(“Expected counter value: %d “, NUM_ITERATIONS * NUM_THREADS);
return 0;
}
COMP3230 Mini-lab 4 Page 2