Path: utzoo!attcan!uunet!ingr!madhat!alvitar
From: alvitar@madhat.UUCP (Phil Harbison)
Newsgroups: comp.unix.wizards
Subject: Re: How can I read keyboard without stopping
Message-ID: <282@madhat.UUCP>
Date: 23 Aug 88 00:48:47 GMT
References: <813@ms3.UUCP> <1246@mcgill-vision.UUCP> <12251@ncoast.UUCP>
Organization: DataVision, Huntsville AL
Lines: 39

In article <813@ms3.UUCP>, isns02@ms3.UUCP (Harris Reavin) writes:
> I would like to know if it is possible to get input data from the
> keyboard while my program is constantly looping and displaying output
> to the screen.  The input comes from a call to "popen()".

The  best  way  I've  found to do this is to spawn a separate process to
handle  the keyboard and communicate using pipes.  I have a program that
performs  an  I/O multiplexing function.  It must simultaneously monitor
the keyboard and the output of a pipe, sending data from the pipe to the
display,  and  data  from  the  keyboard to a subprocess.  I have fork a
couple  of  "handler"  processes,  one  for the keyboard and one for the
subprocess.   The handlers collect their data using blocking reads, then
send  the  data through a pipe to the main process using a simple packet
protocol.  The main process does a blocking read on the pipe waiting for
the  next packet, and can tell by the packet ID whether it came from the
keyboard or the subprocess.  The packets look like this:

	+-----------+------------+------+
	| source-id | byte count | data |
	+-----------+------------+------+

There  are  two nice side effects of this implementation.  The same code
runs  on  v7,  BSD, and USG flavors of UNIX, and probably any version of
UNIX or UNIX-derivatives which support atomic writes to pipes and fstat.
Previous  versions  of this code used select for BSD, non-blocking reads
for  USG,  and punted on v7.  Checking for type-ahead is now easy, since
the  main  process  can perform an fstat to find out if there is data in
the pipe. 

In article <12251@ncoast.UUCP>, Brandon S. Allbery writes:
> +---------------
> | 3) FIONREAD.  BSD systems have an ioctl you can apply to a terminal
> |    line to get the number of characters queued ...
> 
> System V does not.  Xenix has rdchk(fd).  (I wish AT&T would pick it up!)

Unisoft's  version  of  System V has FIONREAD, but unfortunately it only
works when the tty is in cooked mode!  In most cases where I want to use
FIONREAD, the tty is in raw mode.