source: trunk/threads-sem.c

/* Copyright (C) 2009 by Mattia Monga <mattia.monga@unimi.it> */
/* $Id$ */

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sched.h>
#include <semaphore.h>

void down(sem_t *s){ 
        if (sem_wait(s) < 0){
                perror("Errore semaforo (down)");
                exit(1);
        }
}

void up(sem_t *s){
        if (sem_post(s) < 0){
                perror("Errore semaforo (up)");
                exit(1);
        }
}

int shared = 0;
pthread_t p1, p2;
sem_t ss;

void* run(void* s){
        while (down(&ss), 
               shared < 10) {
                sleep(1);
                printf("Processo thread (%p). s = %d\n", 
                       pthread_self(), shared);
                if (!(shared < 10)){
                        printf("Corsa critica!!!!\n");
                        abort();
                }
                shared += 1;
                up(&ss);
                pthread_yield();
        }
        up(&ss);
        return NULL;
}



int main(void){

        if (sem_init(&ss, 
                     0 /* thread local semaphore */,
                     1 /* init value */
                    ) < 0){
                perror("Errore semaforo");
                exit(1);
        }

        pthread_create(&p1, NULL, run, NULL);
        pthread_create(&p2, NULL, run, NULL);

        pthread_join(p1, NULL);
        pthread_join(p2, NULL);
        
        sem_destroy(&ss);
        
        return 0;
}

    
        
  



/* Local Variables: */
/* compile-command: "make -k " */
/* End: */