// to compile: gcc ex2.c -o ex2 -lpthread
// to execute: ex2
// Code uses POSIX Semaphores (IEEE Std 1003.1b).
//
// copyrights: Paulo S. L. de Souza and Davi J. Conte
//

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

#define THREADS 6
#define MAXITER 10

//global
sem_t permit[THREADS]; // um semáforo para cada thread
sem_t sem_master;
int iter;

// função para threads 1
void *slave1(void *p_arg){
    int p, next;

	p = (int) *((int *)p_arg);
	next = p + 1;

    while(1){
        sem_wait(&permit[p]);
        if(iter == MAXITER){
            pthread_exit(0);
        }
        printf("Thread(1) %d, iter = %d\n", p, iter);
        sem_post(&permit[next]);
    }
}

// função para threads 2
void *slave2(void *p_arg){
    int p, next;

	p = (int) *((int *)p_arg);
    
    while(1){
        sem_wait(&permit[p]);
        if(iter == MAXITER){
            pthread_exit(0);
        }
        printf("Thread(2) %d, iter = %d\n", p, iter);
        sem_post(&sem_master);
    }
}

int main(void){
    pthread_t handle[THREADS];
    int i, p[THREADS], initial = 0;
    sem_init(&sem_master, 0, initial);
    // cria threads e semáforos
    for (i=0; i < THREADS; i++) {
        p[i] = i;
	sem_init (&permit[i], 0 , initial);
        if (i%2 == 0){
            if (pthread_create(&handle[ i ], 0, (void *) slave1, (void *) &p[ i ] ) != 0) { 
			    printf("Error creating thread %d! Exiting! \n", i);
			    fflush(0);
    			exit(0);
		    }
        }else{
            if (pthread_create(&handle[ i ], 0, (void *) slave2, (void *) &p[ i ] ) != 0) { 
			    printf("Error creating thread %d! Exiting! \n", i);
			    fflush(0);
			    exit(0);
		    }
        }
    }
    
    // loop iter
    for(iter=0; iter<MAXITER; iter++){
        //Incrementa semáforo para liberar cada thread
        for(i=0; i<THREADS; i+=2){
            sem_post(&permit[i]);
        }

        //Bloqueado aguardando o post de cada thread
        for(i=1; i<=THREADS; i+=2){
            sem_wait(&sem_master);
        }
        printf("Iter = %d\n", iter);
    }
}