C编程中的多线程写入和输出文件

Question

I'm a novice in C and trying to learn Multi Threading. I played aroud with a C program counting to 100000 with 2 threads and outputing to text. However, my program seem to have seg. fault. I cannot figure it out. Please Help:)

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

#define COUNT_TO 100000
#define MAX_CORES 2

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
long long i = 0;


void *start_counting(FILE *out) 
{
    //lock
    pthread_mutex_lock(&mutex);

    while (i < COUNT_TO) 
    {
        ++i;

        printf("i = %lld\n", i);
        fprintf(out,"i = %lld\n", i);
    }

    //lock
    pthread_mutex_unlock(&mutex);
}


int main(void) 
{
    int i = 0;

    FILE *out;
    out = fopen("output.txt","w");

    // create a thread group the size of MAX_CORES
    pthread_t *thread_group = malloc(sizeof(pthread_t) * MAX_CORES);

    // start all threads to begin work
    for (i = 0; i < MAX_CORES; ++i) 
    {
        pthread_create(&thread_group[i], NULL, start_counting(out), NULL);
    }

    // wait for all threads to finish
    for (i = 0; i < MAX_CORES; ++i) 
    {
        pthread_join(thread_group[i], NULL);
    }

    fclose(out);

    return EXIT_SUCCESS;
}

Answer 1

You have a error in this call:

pthread_create(&thread_group[i], NULL, start_counting(out), NULL);

It should be:

pthread_create(&thread_group[i], NULL, start_counting, out);

Please refer to the manual at https://man7.org/linux/man-pages/man3/pthread_create.3.html