/*
    pthreads-with-race.c
    Jeff Ondich, 12 April 2004
    Updated 20 May 2019

    A simple threaded program with a shared integer and
    a race condition.

    To compile:

        gcc -Wall -o pthreads_with_race pthreads_with_race.c

    On some systems, you might need:

        gcc -Wall -o pthreads_with_race pthreads_with_race.c -lpthreads
*/

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

int gSharedInteger = 0;

void *threadMainA(void *arg);
void *threadMainB(void *arg);

int main() {
    pthread_t threadA, threadB;

    /* Spawn the threads. */
    if (pthread_create(&threadA, NULL, threadMainA, 0) != 0) {
        perror("Can't create thread A");
        exit(1);
    }

    if (pthread_create(&threadB, NULL, threadMainB, 0) != 0) {
        perror( "Can't create thread B" );
        exit( 1 );
    }

    /* Wait for threads to return.  If you don't wait for them, the
       process will return from main(), and thus shut down the whole
       process, including the threads. */

    pthread_join(threadA, NULL);
    pthread_join(threadB, NULL);

    return 0;
}

void *threadMainA(void *arg) {
    while(1) {
        gSharedInteger = 25;
    }

    return NULL;
}

void *threadMainB(void *arg) {
    while(1) {
        gSharedInteger = 37;
        if (gSharedInteger != 37) {
            fprintf(stderr, "Uh-oh. Race condition.\n");
            fflush(stderr);
        }
    }

    return NULL;
}