From: Ben Giddings <bg-rubytalk@...>
Date: 2004-06-10T10:39:05+09:00
Subject: Re: oddities with select

On Jun 9, 2004, at 11:43, Ara.T.Howard wrote:
> On Wed, 9 Jun 2004, Ben Giddings wrote:
> didn't you say something about your socket being in non-blocking mode? 
>  if so,
> isn't this just a busy loop since select will keep returning 'true - a 
> read
> will not block':

I'm pretty sure that the timeout parameter is what tells select whether 
or not to block.  I think the nonblocking flag only affects reading 
type operations, like 'recv' or 'read'.  If you're using blocking 
sockets, they wait until there's input, if you're using nonblocking IO, 
they return immediately, either with data or without.  Select is used 
(I think generally with blocking IO) to test to see if there's any 
point in attempting a read, to avoid blocking when no data will be 
read.

If there's no serial traffic, it should return my socket if there's 
input to be read, otherwise it should return nil.

> if not in non-blocking mode, perhaps your pattern is bad?  what 
> happens if you
> do this:
>
> <snip>
>>         while true
>>           if select([@sock], [], [], 0.1)
>>             retval += @sock.recv(256)
>               p retval
> </snip>
>
> ??
>
> do you see retval growing?

No, in those cases when there's some data there but 'select' doesn't 
see it, I don't see anything being appended to 'retval' and I get an 
empty string back.

Thanks for the ideas though,

Ben