/*
 * sem2.c - Shows that semaphores are NOT locks, but a signalling
 *          mechanism.  Multiple posts to a semaphore incremenet
 *          the count regardless of the current value
 */

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

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

// start flag 
volatile int start;

// flag semaphore
sem_t flag;

// The thread process
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++)
    {
        sem_wait(&flag);
        // this is the critical section
        counter1++;
        counter2++;
        // leaving critical section
        sem_post(&flag);

        if(me == 0) {
            sem_post(&flag);
        }
    }

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

    return NULL;
}


// Main process
int main()
{
    int val1 = 0;
    int val2 = 1;

    sem_init(&flag, 0, 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);

    sem_destroy(&flag);
    return EXIT_SUCCESS;
}