Learning C: pthread and mqueue

main.c

#include <mqueue.h>
#include <pthread.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

const char *QUEUE_NAME = "/foo";
const char *MESSAGE = "hi\n";

void *one(void *arg) {
        pthread_detach(pthread_self());
        mqd_t mqd = mq_open(QUEUE_NAME, O_WRONLY);
        int *seconds = (int *)arg;
        mq_send(mqd, "asdf\n", strlen("asdf\n") + 1, 1);
        printf("DEBUG: Thread %ld sleeping for %d seeconds...\n", pthread_self(), *seconds);
        sleep(*seconds);
        printf("DEBUG: Thread %ld woke up after %d seconds!!\n", pthread_self(), *seconds);
        mq_send(mqd, MESSAGE, strlen(MESSAGE) + 1, 1);
}

int main() {
        struct mq_attr attr;
        attr.mq_flags = 0;
        attr.mq_maxmsg = 10;
        attr.mq_msgsize = 33;
        attr.mq_curmsgs = 0;
        mqd_t mqd = mq_open(QUEUE_NAME, O_CREAT | O_RDWR, 0644, &attr);
        if (mqd == -1) {
                char *error;
                sprintf(error, "ERROR: queue %s", QUEUE_NAME);
                perror(error);
                return 1;
        }
        printf("DEBUG: file descriptor: %d\n", mqd);

        pthread_t ptid;
        int second1, second2, second3;

        second3 = 3;
        if (pthread_create(&ptid, NULL, one, &second3)) {
                perror("ERROR: could not start thread\n");
                return 1;
        }
        printf("DEBUG: Created thread %ld\n", ptid);
        second1 = 1;
        if (pthread_create(&ptid, NULL, one, &second1)) {
                perror("ERROR: could not start thread\n");
                return 1;
        }
        printf("DEBUG: Created thread %ld\n", ptid);

        second2 = 2;
        if (pthread_create(&ptid, NULL, one, &second2)) {
                perror("ERROR: could not start thread\n");
                return 1;
        }
        printf("DEBUG: Created thread %ld\n", ptid);

        char msg_ptr[1000000];
        int should = 0;
        while(should < 6) {
                if (mq_receive(mqd, msg_ptr, 1000000, NULL) != -1) {
                        printf("DEBUG: Message from thread: %s\n", msg_ptr);
                        should++;
                }
        }
        mq_close(mqd);
        mq_unlink(QUEUE_NAME);
        return 0;
}

Makefile

all:
        gcc main.c -lpthread -lrt