Creating threads in C

pthread_create starts a thread running one function; pthread_join waits for it.

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

static void *worker(void *arg) {
    long id = *(long *) arg;
    printf("worker %ld\n", id);
    return arg;
}

int main(void) {
    pthread_t threads[3];
    long ids[3] = {0, 1, 2};

    for (int i = 0; i < 3; i++) {
        if (pthread_create(&threads[i], NULL, worker, &ids[i]) != 0) {
            return 1;
        }
    }
    for (int i = 0; i < 3; i++) {
        void *result = NULL;
        pthread_join(threads[i], &result);
        printf("joined %ld\n", *(long *) result);
    }
    return 0;
}

How it works

1. The thread function takes and returns void *.
2. Each thread needs its own argument, never a shared loop variable.
3. Joining is what makes the result and the cleanup safe.

Keywords and builtins used here

• NULL
• for
• if
• int
• long
• main
• return
• static
• void
• worker

The run, in numbers

Lines

25

Characters to type

455

Tokens

165

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 99 seconds.

Type this snippet

Step 1 of 3 in Starting threads, step 1 of 10 in Threads & concurrency.

Next →