#include "apue.h"#include <fcntl.h>#include <sys/mman.h>#define	NLOOPS		1000#define	SIZE		sizeof(long)	/* size of shared memory area */static intupdate(long *ptr){	return((*ptr)++);	/* return value before increment */}intmain(void){	int		fd, i, counter;	pid_t	pid;	void	*area;	if ((fd = open("/dev/zero", O_RDWR)) < 0)		err_sys("open error");	if ((area = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,	  fd, 0)) == MAP_FAILED)		err_sys("mmap error");	close(fd);		/* can close /dev/zero now that it's mapped */	TELL_WAIT();	if ((pid = fork()) < 0) {		err_sys("fork error");	} else if (pid > 0) {			/* parent */		for (i = 0; i < NLOOPS; i += 2) {			if ((counter = update((long *)area)) != i)				err_quit("parent: expected %d, got %d", i, counter);			TELL_CHILD(pid);			WAIT_CHILD();		}	} else {						/* child */		for (i = 1; i < NLOOPS + 1; i += 2) {			WAIT_PARENT();			if ((counter = update((long *)area)) != i)				err_quit("child: expected %d, got %d", i, counter);			TELL_PARENT(getppid());		}	}	exit(0);}