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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: HELP PLEASE: select() in BSD
Message-ID: <8630@mimsy.UUCP>
Date: Thu, 17-Sep-87 20:53:27 EDT
Article-I.D.: mimsy.8630
Posted: Thu Sep 17 20:53:27 1987
Date-Received: Sat, 19-Sep-87 18:17:04 EDT
References: <307@picuxa.UUCP> <891@mtund.ATT.COM>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 37
Keywords: poll
Summary: How is this `better'?

In article <891@mtund.ATT.COM> bfb@mtund.ATT.COM (Barry Books) writes:
>[System] 5.3 includes a better select() called poll().  Poll takes
>an array of pollfd's a long which is the number in the array and a
>timeout in milliseconds.  You can also get a signal when there is
>something waiting to poll on.

Select takes three pointers to `fd_set's, an int which specifies how
many descriptors are described by the `fd_set's, and a timeout in
microseconds.  You can also get a signal (SIGIO) when a descriptor is
ready.

So what makes poll better?

For the original poster:

	int
	select(int nfd, fd_set *r, fd_set *w, fd_set *ex,
		struct timeval *timeout)

or (4.2BSD)

	int
	select(int nfd, int *r, int *w, int *ex, struct timeval *timeout)

returns the number of descriptors that are ready for r(eading),
w(riting), or that have ex(ceptions), returning within the time
limit given by timeout, or waiting until at least one is ready if
timeout==NULL.  select always returns immediately if at least one
descriptor is ready.  *r, *w, and *ex are modified before select
returns to reflect which descriptors in fact were readable or
writable or had exceptional conditions pending.

[Okay, Exceptional Conditions amount to out of band data on
sockets.]
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris