From: Tom Pollard <tomp@...>
Date: 2006-11-01T09:08:14+09:00
Subject: Re: Nonblocking IO read


On Oct 31, 2006, at 6:23 PM, ara.t.howard@noaa.gov wrote:
> On Wed, 1 Nov 2006 srobertjames@gmail.com wrote:
>> How can I perform a nonblocking IO read?  That is, read whatever  
>> is there to read and return.  If there's nothing yet, just return.

That's what the Unix read() function does ("man 2 read"), available  
in Ruby as IO#sysread().  The ri documentation doesn't explain much  
about how to use Ruby's sysread, unfortunately.

>> Failing that, is there a way to manually check if there's anything  
>> to read or the read will block?
>>
>> (Note that I'm developing for both 'nix and Windows.)

The select() function (Kernel#select, in Ruby) is the standard way to  
do IO multiplexing under Unix.  You give it a list of file handles on  
which you're waiting to be able to read or write, and it returns when  
one or more of them is ready.   Windows provides a select() function,  
too, but it only supports sockets (not pipes or ordinary file IO.)   
The Win32 API generally doesn't provide non-blocking IO methods,  
because it's assumed you'll use threads if you want to do something  
else while waiting for IO.

> it can't be done.  search the archives, this sort of thing almost  
> always
> indicates a design flaw.  for instance - what will your program do  
> if there is
> no input?

Check other IO channels, wait for other sorts of events, do work -  
whatever.  Where do come from asserting that the use of non-blocking  
IO represents a "design flaw"?

Tom