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From: dupuy@amsterdam.columbia.edu (Alexander Dupuy)
Newsgroups: comp.unix.questions
Subject: Re: Using select(2) to wait for connect(2)
Message-ID: <3930@columbia.UUCP>
Date: Tue, 25-Nov-86 22:07:49 EST
Article-I.D.: columbia.3930
Posted: Tue Nov 25 22:07:49 1986
Date-Received: Wed, 26-Nov-86 00:14:14 EST
References: <46@otc.OZ>
Sender: nobody@columbia.UUCP
Reply-To: dupuy@amsterdam.columbia.edu (Alexander Dupuy)
Organization: Columbia University CS Department
Lines: 34
Keywords: select sockets AF_UNIX

In article <46@otc.OZ> adjg@otc.OZ (Andrew Gollan) writes:
>I need to have a server that forms a junction between two client
>processes.  Further if one of the clients is not present the other must
>still be serviced.  I read the manual on accept(2) and found that one
>could use select(2) to wait for incoming connections.
>...
>	if (select(2, &mask, (int *)0, (int *)0, 0) < 0)
>...
>The problem:
>	The select in the server never returns. 
>...
>The questions:
>	Am I doing something horribly wrong or is it that select(2)
>	does not perform as documented? Have I missed something in the
>	documentation?

The answer:
	Select(2) does perform as documented.  You missed the note which
describes the timeout (last) argument to select.  "If timeout is a zero pointer
the select blocks indefinitely.  To effect a poll, the timeout argument should
be non-zero, pointing to a zero valued timeval structure."

	You want to "effect a poll" like this:

struct timeval poll = { 0, 0 };

if (select(2, &mask, (int *) 0, (int *)0, &poll) < 0)
    perror ("etc...

@alex

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