select.c

<B>Digital的Unix操作系统VAX 4.2源码</B>

#ifdef lint
static char *sccsid = "@(#)select.c	4.1	(ULTRIX)	7/2/90";
#endif lint

/*
 * Code for various kinds of delays.  Most of this is nonportable and
 * requires various enhancements to the operating system, so it won't
 * work on all systems.  It is included in curses to provide a portable
 * interface, and so curses itself can use it for function keys.
 */


#include "curses.ext"
#include <signal.h>

#define NAPINTERVAL 100

/* From early specs - this may change by 4.2BSD */
struct _timeval {
	long tv_sec;
	long tv_usec;
};

#ifdef FIONREAD
# ifndef TIOCREMOTE
/*
 * Decide if we can emulate select but don't have it.  This is
 * intended to be true only on 4.1BSD, not 4.2BSD or USG.
 */
#  define NEEDSELECT
# endif
#endif

#ifdef NEEDSELECT
/*
 * Emulation of 4.2BSD select system call.  This is somewhat crude but
 * better than nothing.  We do FIONREAD on each fd, and if we have to
 * wait we use nap to avoid a busy wait.  The resolution of the nap
 * will hurt response - so will the fact that we ignore the write fds.
 * If we are simulating nap with a 1 second sleep, this will be very poor.
 *
 * nfds is the number of fds to check - this is usually 20.
 * prfds is a pointer to a bit vector of file descriptors - in the case
 *	where nfds < 32, prfds points to an integer, where bit 1<<fd
 *	is 1 if we are supposed to check file descriptor fd.
 * pwfds is like prfds but for write checks instead of read checks.
 * ms is the max number of milliseconds to wait before returning failure.
 * The value returned is the number of file descriptors ready for input.
 * The bit vectors are updated in place.
 */

int
select(nfds, prfds, pwfds, pefds, timeout)
register int nfds;
int *prfds, *pwfds, *pefds;
struct _timeval *timeout;
{
	register int fd;
	register int rfds = *prfds;
	register int n;
	int nwaiting, rv = 0;
	long ms = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;

	for (;;) {
		/* check the fds */
		for (fd=0; fd<nfds; fd++)
			if (1<<fd & rfds) {
				ioctl(fd, FIONREAD, &nwaiting);
				if (nwaiting > 0) {
					rv++;
				} else
					*prfds &= ~(1<<fd);
			}
		if (rv)
			return rv;

		/* Nothing ready.  Should we give up? */
		if (ms <= 0)
			return 0;

		*prfds = rfds;	/* we clobbered it, so restore. */

		/* Wait a bit */
		n = NAPINTERVAL;
		if (ms < NAPINTERVAL)
			n = ms;
		ms -= n;
		napms(n);
	}
}
#else
#ifndef FIONREAD
int
select(nfds, prfds, pwfds, pefds, ms)
register int nfds;
int *prfds, *pwfds, *pefds;
struct _timeval *ms;
{
	/* Can't do it, but at least compile right */
	return ERR;
}
#endif FIONREAD
#endif NEEDSELECT