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Subject: how to tell if getchar() will block -- select doesn't cut it
Date: Tue, 22 Jul 1997 22:09:10 -0700
From: Paul Traina <pst@shockwave.com>
Sender: owner-freebsd-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

I had some fun this week -- I'd added some asynchronous event code to a
little line editor so that I could deal with some events while waiting
from user input...

The code looked something like:

	<select cruft to wait on several sockets>

	if (read data available on stdin) {
	    c = getchar();
	    go do more processing;
	}

This worked fine and dandy except that pasting into a window running this
program didn't work properly -- characters seemed to get lost.

The obvious problem is that the paste was sending down many characters,
stdio read more than one character and stored it in a local buffer, so
there was data available for getchar(), but of course, the low level buffer
had already been slurped in, so the select wasn't returning true.

I worked around this by checking, in a non-portable fashion, if stdio had
any data available for it (if (fp->_r >= 0 || fp->_ur >= 0)) but quite
frankly, non-portable code sucks.

I did a reasonable perusal of the source code in stdio and I can't seem
to find any portable way to ask the general question:

	Is getchar() going to block if I call it?

Ideas?