#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int myglobal=0; //Variabile globale
pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;

void *thread_incrementa(void *arg)
{ 	
	int i,j;	void *val;
	//for (i=0; i<1000000; i++);
 	pthread_mutex_lock(&mymutex);
	for ( i=0; i<20; i++ ){
		  j=myglobal; //variabile locale temporanea
		  j=j-1;   printf("thread_decr\n"); 
		  myglobal=j;
	}
	pthread_mutex_unlock(&mymutex);
	pthread_exit(val);
}

int main(void){
	pthread_t mythread;	int i;	void *status;
	if(pthread_create(&mythread,NULL,thread_incrementa,NULL) )
	{  printf("errore thread."); 	exit(1);  }
	
	pthread_mutex_lock(&mymutex);
	for ( i=0; i<20; i++) 
	{
		myglobal=myglobal+1;
		printf("main incr\n"); 
	}
	pthread_mutex_unlock(&mymutex);
	if(pthread_join(mythread,(void*)&status)){printf("errore join."); exit(1); }
	printf("\n myglobal uguale %d\n",myglobal);
	exit(0);
}