Multithreaded prime check in C ( using pthread )

main.c

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

#define MAX_THREADS 64
#define MAX_PRIMES 1000

struct thread_info
{
    int low;
    int high;
    int number;
};

volatile int running_threads = 0;
pthread_mutex_t running_mutex = PTHREAD_MUTEX_INITIALIZER;

void *prime_checker_thread(void *params)
{
    struct thread_info *data = (struct thread_info *) params; 

    for(int i = data->low; i < data->high; i++)
    {
        int j = 2;
        bool prime = true;

        while(j * j < i)
        {
            if(i % j == 0)
            {
                prime = false;
            }
            j++;
        }

        if(prime)
        {
            printf("TH: %d\tPRIME: %d\n", data->number, i);
        }
    }

    pthread_mutex_lock(&running_mutex);
    running_threads--;
    pthread_mutex_unlock(&running_mutex);

    return 0;
}

int main()
{
    
    int numbers = MAX_PRIMES;
    int each_thread = numbers / MAX_THREADS;

    struct thread_info thread_info_arr[MAX_THREADS];
    pthread_t threads[MAX_THREADS];
    
    for(int i = 0, j = 0; i < numbers - each_thread; i += each_thread, j++)
    {
        thread_info_arr[j].low = i;
        thread_info_arr[j].high = i + each_thread;
        thread_info_arr[j].number = j;

        pthread_mutex_lock(&running_mutex);
        running_threads++;
        pthread_mutex_unlock(&running_mutex);
        pthread_create(&threads[j], NULL, prime_checker_thread, &thread_info_arr[j]);
    }

    while (running_threads > 0);

    return 0;
}