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From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.unix.internals,comp.unix.sysv386
Subject: Can you poll a pipe?
Message-ID: <1990Oct24.184556.853@esegue.segue.boston.ma.us>
Date: 24 Oct 90 18:45:56 GMT
Reply-To: johnl@iecc.cambridge.ma.us (John R. Levine)
Distribution: na
Organization: I.E.C.C., Cambridge MA
Lines: 22

I am writing some X code in which I want to display items to the screen as
they arrive from a back end via a pipe.  To do a reasonable job, I need to
read both X events and pipe data at the same time.  Under Sys V, there is
a handy poll() call similar to the BSD select() call that lets you wait until
there is activity on any of a set of file descriptors.

The problem is that, according to the manual, poll() is only guaranteed to
work on Streams devices.  A little experimentation shows that under ISC 2.2
polling a pipe works nicely, but it's not clear whether that is standard
behavior or an ISC improvement.  (There is such a thing as a streams pipe,
but the standard pipe system call doesn't make one, it makes a nameless FIFO,
as usual.)

Does anyone with experience with other Sys V versions know whether polling
pipes is always supposed to work?  Since I only need to do this under X, we
can assume that streams are in the kernel, since without them X won't work.

TIA,
-- 
John R. Levine, IECC, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@esegue.segue.boston.ma.us, {ima|spdcc|world}!esegue!johnl
Atlantic City gamblers lose $8200 per minute. -NY Times