Path: utzoo!attcan!uunet!ginosko!aplcen!haven!ames!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.sys.sgi
Subject: Re: HELP: Low level terminal I/O
Summary: use select(2)
Message-ID: <39141@sgi.SGI.COM>
Date: 28 Jul 89 19:39:18 GMT
References: <8907201857.aa12017@SMOKE.BRL.MIL>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 29

In article <8907201857.aa12017@SMOKE.BRL.MIL>, mis@APL.STANFORD.EDU (Misha Pavel) writes:
> ...
> I was hoping that the term.c_cc[VTIME] = 0 would do the job.
> But the system seems to  be still waiting for at least one char.
> 
> Is there any way to look at the system buffer and or return
> from read() when no input was generated?
> ...
> 
> Misha Pavel <mis@psych.Stanford.Edu>

System V has a confusing notion of VTIME/VMIN.  It likes to wait for at
least one character.  I seem to recall that there is a combination which
does not wait, but there is no reason to suffer the pain of reading the
SVID (the only place I know where it is half way documented), or of reading
either SGI's stty_ld.c or the standard SVR3 line discipline code.

You could use the FIONNBIO ioctl(2) on an FD that is a tty or socket.

I would use select(2) instead.  Select(2) has always worked on streams
(tty's) and sockets.  It allows fine grain timeouts and simultaneous
polling of lots of FD's, for reading and/or writing.  It now works on
everything.  Now is 3.2, or maybe some version of 3.1.  It was added to
lboot(1), cdev[], etc. seemingly a long time ago.


Vernon Schryver
Silicon Graphics
vjs@sgi.com