Race Condition in Multi-threaded C Application Using Pthreads and Mutexes
I've spent hours debugging this and I can't seem to get I've been banging my head against this for hours... This might be a silly question, but I'm encountering a race condition in my multi-threaded C application that uses the Pthreads library, where two threads are accessing and modifying a shared variable without proper synchronization. The shared variable is an integer that counts the number of processed items. I have implemented a mutex to protect this variable, but I'm still seeing inconsistent results. Here's the relevant portion of my code: ```c #include <stdio.h> #include <stdlib.h> #include <pthread.h> #define NUM_THREADS 5 #define NUM_ITERATIONS 1000 pthread_mutex_t lock; int counter = 0; void* increment_counter(void* arg) { for (int i = 0; i < NUM_ITERATIONS; i++) { pthread_mutex_lock(&lock); counter++; pthread_mutex_unlock(&lock); } return NULL; } int main() { pthread_t threads[NUM_THREADS]; pthread_mutex_init(&lock, NULL); for (int i = 0; i < NUM_THREADS; i++) { pthread_create(&threads[i], NULL, increment_counter, NULL); } for (int i = 0; i < NUM_THREADS; i++) { pthread_join(threads[i], NULL); } printf("Final counter value: %d\n", counter); pthread_mutex_destroy(&lock); return 0; } ``` When I run this program, I expect the final counter value to be 5000 (5 threads * 1000 iterations each). However, I often see values like 4997 or 5001, indicating that some increments are missed or counted multiple times. I've double-checked that Iām locking and unlocking the mutex correctly, and I also ensured that no other parts of the code are modifying `counter` without locks. Iām compiling this code with `gcc -pthread -o my_program my_program.c` on Ubuntu 22.04 with GCC 11.2.0. Is there something I might be missing in my usage of mutexes or is there a common pitfall with thread synchronization that I should be aware of? Any suggestions on how to debug this further would be greatly appreciated! For context: I'm using C on Ubuntu. I'd really appreciate any guidance on this. My development environment is Linux. Any ideas what could be causing this? What's the correct way to implement this?