CODEWITHSUNDEEP
cmultithreadingsegmentation-faultpthreadsmutex
Chris Fretz
Chris Fretz

Reputation: 437

Pthread Mutex Segfault

I've never worked with pthreads before and am simply trying to familiarize myself with them. As such, I've written the following test code:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

int count = 0;

void *increment(void *tex);

int main(int argc, char **argv) {
    pthread_t t1, t2, t3;
    pthread_mutex_t mutex;
    pthread_mutex_init(&mutex, NULL);
    pthread_create(&t1, NULL, &increment, &mutex);
    pthread_create(&t2, NULL, &increment, &mutex);
    pthread_create(&t2, NULL, &increment, &mutex);
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    pthread_join(t3, NULL);
    printf("Value of count is: %d\n", count);
}

void *increment(void *tex) {
    pthread_mutex_t *mutex = (pthread_mutex_t *) mutex;
    for (int i = 0; i < 100; i++) {
        pthread_mutex_lock(mutex);
        count++;
        pthread_mutex_unlock(mutex);
    }
    return NULL;
}

I'm compiling the code with GCC using the proper -pthread flag, yet, for whatever reason, any time that any of the threads reach the mutex locking line, segfault. Upon further investigation with GDB, I've discovered that the mutex pointer appears to be invalid inside of the increment function even though I initialized it in main, passed it in as the argument to pthread_create, and have called join on each thread to ensure that main is still in scope. I'm at a loss for why this is happening, and could use some help. Thanks!

Upvotes: 1

Views: 2199

Answers (1)

Sean
Sean

Reputation: 62472

You've got:

pthread_mutex_t *mutex = (pthread_mutex_t *) mutex;

what you need is:

pthread_mutex_t *mutex = (pthread_mutex_t *) tex;

Upvotes: 3

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