From: nobu.nokada@...
Date: 2003-06-17T09:05:40+09:00
Subject: Re: popen, rsh, and File::NONBLOCK

Hi,

At Tue, 17 Jun 2003 06:17:25 +0900,
ahoward wrote:
> this a bit of *nix question, but, using pipes, how does one either
> 
>   a) determine if an IO.gets/read etc would block

io/wait in rough provides IO#ready?.

$ ruby -rio/wait -e 'cat = IO.popen "cat", "r+";cat.puts "foobar";sleep 0.1;p cat.ready?;p cat.gets;p cat.ready?'
7
"foobar\n"
nil

> or
> 
>   b) use non-blocking io with pipes

Also nonblock.rb is in io/wait.

$ ruby -rio/nonblock -e 'cat = IO.popen "cat", "r+";cat.nonblock=true;cat.puts "foobar";p cat.gets;p cat.read(1)'
"foobar\n"
-e:1:in `read': Resource temporarily unavailable (Errno::EAGAIN)
	from -e:1

Note that IO#gets waits till a newline even in non-blocking
mode.

> this certainly does not work...
> 
> ~/eg/ruby > irb
> irb(main):001:0> cat = IO.popen 'cat', File::RDWR | File::NOCTTY | File::NONBLOCK

Only access mode has meanings in the second argument to
IO.popen.  NONBLOCK is ignored here.

# NOCTTY affects to only terminal device.

> does popen then not respect the File::NONBLOCK?  perhaps this is a limitation
> of pipes themselves then...

Basically, pipe(2) doesn't take optional flags.  IO.popen just
follows it.  It would be possible to treat the flag as
special...

-- 
Nobu Nakada