Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!udel!gatech!mcnc!rti!trt
From: trt@rti.UUCP (Thomas Truscott)
Newsgroups: comp.unix.wizards
Subject: Re: Efficiency of detecting input FD after SIGIO?
Keywords: SIGIO, socket, select, ioctl
Message-ID: <2023@rti.UUCP>
Date: 8 Feb 88 16:25:12 GMT
References: <108@titan.SW.MCC.COM>
Organization: Research Triangle Institute, RTP, NC
Lines: 22

In <108@titan.SW.MCC.COM>, janssen@titan.SW.MCC.COM (Bill Janssen) writes:
> I have a program that has between 1 and 20 sockets open.
> It receives SIGIO when input is available on some one of them.
> 80% of the time there is only one open socket.
> Given this, what is the most efficient way to tell what fd the input
> is available on?

Well, it sounds like 80% of the time you *know* what fd the input is available
on, so you can just read the data (you might consider non-blocking I/O).

If there is more than one fd just use select().
Calls like select() are why BSD is so much better than System V.
But if you can't resist optimizing things,
do a (non-blocking) read of the fd you think has the data.
If it indeed has data you avoid the overhead of the select().

I find signal handling to be a dangerous business,
and recommend against it.  Do you really need SIGIO?
What is the program doing in the meantime?
If it is just reading from a terminal, put the select()
on that as well and you win all around.
	Tom Truscott