Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!psuvax1!brutus.cs.uiuc.edu!uakari.primate.wisc.edu!aplcen!uunet!sco!natei
From: natei@sco.COM (Nathaniel Ingersoll)
Newsgroups: comp.unix.wizards
Subject: Re: sockets and select
Keywords: socket select
Message-ID: <4990@scolex.sco.COM>
Date: 27 Feb 90 18:31:41 GMT
References: <4309@helios.TAMU.EDU> <132218@sun.Eng.Sun.COM>
Reply-To: natei@sco.COM (Nathaniel Ingersoll)
Distribution: usa
Organization: The Santa Cruz Operation, Inc.
Lines: 28

In article <4309@helios.TAMU.EDU> dhess@cs.tamu.edu (David K Hess)
asks why select() for reading on an NDELAY socket always seems to
return a fact that the socket has data.

The manual page:
.
.     SELECT(S)		       UNIX System V		     SELECT(S)
.     ...
.     Description
.	  select examines the I/O descriptor sets whose	addresses are
.	  passed in readfds, writefds, and exceptfds to	see if some of
.	  their	descriptors are	ready for reading, are ready for
.	  writing, or have an exceptional condition pending,
.	  respectively.	 The first nfds	descriptors are	checked	in

"Ready" for reading/writing probably means that the read or the write
will filled without blocking, and since the NDELAY bit has been set,
read() will always work without blocking.

You should either
	(use NDELAY && not use select())
		||
	(use select() && not NDELAY)
-- 
________________________________________________________________________________
  I told the police that I was not injured,
  but on removing my hat, I found that I
  had a skull fracture.                     -- from an insurance accident form