/* Spawn N threads that print their TID with pthread_self and other
 * ID-like information for multiple threads.
 *
 * https://cirosantilli.com/linux-kernel-module-cheat#pthreads
 *
 * Usage:
 *
 * ....
 * ./pthread_self.out [nthreads]
 * ....
 *
 * Sample usage:
 *
 * ....
 * ./pthread_self.out [nthreads]
 * ....
 *
 * Sample output:
 *
 * ....
 * 0 tid: 139852943714048
 * tid, getpid(), pthread_self() = 0, 13709, 139852943714048
 * tid, getpid(), pthread_self() = 1, 13709, 139852935321344
 * 1 tid: 139852935321344
 * 2 tid: 139852926928640
 * tid, getpid(), pthread_self() = 2, 13709, 139852926928640
 * 3 tid: 139852918535936
 * tid, getpid(), pthread_self() = 3, 13709, 139852918535936
 * ....
 *
 * Note how the PID is the same for all threads.
 *
 * There is then a Linux specific gettid which returns a really unique thread ID:
 * https://stackoverflow.com/questions/9305992/if-threads-share-the-same-pid-how-can-they-be-identified#comment42637433_9306150
 * man gettid says that this value is different than pthread_self.
 */

#define _XOPEN_SOURCE 700
#include <assert.h>
#include <errno.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

void* main_thread(void *arg) {
    int argument;
    argument = *((int*)arg);
    printf(
        "tid, getpid(), pthread_self() = "
        "%d, %ju, %ju\n",
        argument,
        (uintmax_t)getpid(),
        (uintmax_t)pthread_self()
    );
    return NULL;
}

int main(int argc, char**argv) {
    pthread_t *threads;
    unsigned int nthreads, nwaves, i, *thread_args, wave;
    int rc;

    /* CLI arguments. */
    if (argc > 1) {
        nthreads = strtoll(argv[1], NULL, 0);
    } else {
        nthreads = 1;
    }
    if (argc > 2) {
        nwaves = strtoll(argv[2], NULL, 0);
    } else {
        nwaves = 1;
    }
    threads = malloc(nthreads * sizeof(*threads));
    thread_args = malloc(nthreads * sizeof(*thread_args));

    for (wave = 0; wave < nwaves; wave++) {
        /* main thread for comparison. */
        printf(
            "tid, getpid(), pthread_self() = "
            "main, %ju, %ju\n",
            (uintmax_t)getpid(),
            (uintmax_t)pthread_self()
        );

        /* Create all threads */
        for (i = 0; i < nthreads; ++i) {
            thread_args[i] = i;
            rc = pthread_create(
                &threads[i],
                NULL,
                main_thread,
                (void*)&thread_args[i]
            );
            if (rc != 0) {
                errno = rc;
                perror("pthread_create");
                exit(EXIT_FAILURE);
            }
            assert(rc == 0);
            printf("%d tid: %ju\n", i, (uintmax_t)threads[i]);
        }

        /* Wait for all threads to complete */
        for (i = 0; i < nthreads; ++i) {
            rc = pthread_join(threads[i], NULL);
            if (rc != 0) {
                printf("%s\n", strerror(rc));
                exit(EXIT_FAILURE);
            }
        }
    }

    /* Cleanup. */
    free(thread_args);
    free(threads);
    return EXIT_SUCCESS;
}