/*
 * con3.c - Concurrency using flag array - version 2
 *          Move setting of the flag before the wait
 *          Allows threads to specify desire for critical secgion
 *          Due to race conditions with the flag array, it is prone to deadlock
 *          if both threads set the flag at the same time
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>

// shared global
static int counter1 = 0;
static int counter2 = 0;

// start flag
volatile int start = 0;

// flag array
volatile int flag[2] = {0,0};

void* thread_routine(void* args)
{
    int me = *((int *) args);
    int you = me ? 0 : 1;

    printf("Worker thread: %d ready, you are %d\n",me,you);

    // wait for start from master thread
    while(!start);

    for (int j = 0; j < 100000000; j++)
    {
        flag[me]=1;
        while(flag[you])
        {
            /* do nothing */
        }
        // this is the critical section
        counter1++;
        counter2++;
        // leaving critical section
        flag[me]=0;
    }

    printf("Worker thread: %d done\n",me);

    return NULL;
}

int main()
{
    int val1 = 0;
    int val2 = 1;

    pthread_t thr1;
    pthread_t thr2;
    if(pthread_create(&thr1, NULL, thread_routine, (void*)&val1) == -1) {
        printf("COULD NOT CREATE A THREAD\n");
        exit(EXIT_FAILURE);
    }
    if(pthread_create(&thr2, NULL, thread_routine, (void*)&val2) == -1) {
        printf("COULD NOT CREATE A THREAD\n");
        exit(EXIT_FAILURE);
    }

    start = 1;

    pthread_join(thr1,NULL);
    pthread_join(thr2,NULL);

    printf("counter1: %d\n",counter1);
    printf("counter2: %d\n",counter2);
    return EXIT_SUCCESS;
}