#include	"unp.h"#define	PORT		9999#define	ADDR		"127.0.0.1"#define	MAXBACKLOG	100			/* globals */struct sockaddr_in	serv;pid_t				pid;	/* of child */int			pipefd[2];#define	pfd	pipefd[1]	/* parent's end */#define	cfd	pipefd[0]	/* child's end */			/* function prototypes */void	do_parent(void);void	do_child(void);intmain(int argc, char **argv){	if (argc != 1)		err_quit("usage: backlog");	Socketpair(AF_UNIX, SOCK_STREAM, 0, pipefd);	bzero(&serv, sizeof(serv));	serv.sin_family = AF_INET;	serv.sin_port = htons(PORT);	Inet_pton(AF_INET, ADDR, &serv.sin_addr);	if ( (pid = Fork()) == 0)		do_child();	else		do_parent();			exit(0);}voidparent_alrm(int signo){	return;		/* just interrupt blocked connect() */}voiddo_parent(void){	int		backlog, j, k, junk, fd[MAXBACKLOG + 1];	Close(cfd);	Signal(SIGALRM, parent_alrm);	for (backlog = 0; backlog <= 14; backlog++) {		printf("backlog = %d: ", backlog);		Write(pfd, &backlog, sizeof(int));	/* tell child value */		Read(pfd, &junk, sizeof(int));		/* wait for child */		for (j = 1; j <= MAXBACKLOG; j++) {			fd[j] = Socket(AF_INET, SOCK_STREAM, 0);			alarm(2);			if (connect(fd[j], (SA * ) &serv, sizeof(serv)) < 0) {				if (errno != EINTR)					err_sys("connect error, j = %d", j);				printf("timeout, %d connections completed\n", j-1);				for (k = 1; k < j; k++)					Close(fd[k]);				break;	/* next value of backlog */			}			alarm(0);		}		if (j > MAXBACKLOG)			printf("%d connections?\n", MAXBACKLOG);	}	backlog = -1;		/* tell child we're all done */	Write(pfd, &backlog, sizeof(int));}voiddo_child(void){	int		listenfd, backlog, junk;	const int	on = 1;	Close(pipefd[1]);	Read(cfd, &backlog, sizeof(int));	/* wait for parent */	while (backlog >= 0) {		listenfd = Socket(AF_INET, SOCK_STREAM, 0);		Setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));		Bind(listenfd, (SA *) &serv, sizeof(serv));		Listen(listenfd, backlog);		/* start the listen */		Write(cfd, &junk, sizeof(int));	/* tell parent */		Read(cfd, &backlog, sizeof(int));/* just wait for parent */		Close(listenfd);	/* closes all queued connections too */	}}