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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards
Subject: Re: Non-blocking accept(2) calls
Message-ID: <8395@mimsy.UUCP>
Date: Thu, 3-Sep-87 22:38:37 EDT
Article-I.D.: mimsy.8395
Posted: Thu Sep  3 22:38:37 1987
Date-Received: Sat, 5-Sep-87 13:54:45 EDT
References: <479@radio.toronto.edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 46
Keywords: socket non-blocking BSD
Summary: use listen followed by select-for-read

In article <479@radio.toronto.edu> brian@radio.toronto.edu (Brian
Glendenning) writes:
>I am writing a graphics "server" on our Sun (3/180, SunOs 3.4=BSD 4.2), which
>I am implementing through socket i/o. When the server is not connected I would
>like to poll accept(2) periodically looking for new connections. It should be
>non-blocking so that it doesn't adversely affect screen activity.
>
>So my question is - how do I make accept non-blocking? I know it can be done.

Instead of making accept nonblocking, perform it only when it will not
block.  To find out when the latter is true, select the service socket
(the one on which you have listen()ed) for reading:

	#include <sys/types.h>
	/* beware, 4.3BSD/V8 macros below */
	fd_set	rset, wset;
	...
		if (listen(serverfd, 5))
			error(...);
		FD_ZERO(&rset);
		FD_SET(serverfd, &rset);
		highfd = serverfd;
		for (;;) {
			fd_set r = rset, w = wset;
			int newfd, sourcesize;
			struct sockaddr_in source;

			nsel = select(highfd, &r, &w, (fd_set *)0,
				(struct timeval *)0);
			if (nsel <= 0) {
				/* if (errno == EINTR) continue; (optional) */
				error(...);
			}
			if (FD_ISSET(serverfd, &r)) {
				sourcesize = sizeof(source);
				newfd = accept(servfd, &source, &sourcesize);
				if (newfd < 0)
					error(...);
				FD_SET(newfd, &rset);
				FD_SET(newfd, &wset);
			}
			...
		}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	seismo!mimsy!chris