From: Bill Kelly <billk@...>
Date: 2005-07-17T07:01:54+09:00
Subject: Re: Nonblocking Sockets

From: "James Edward Gray II" <james@grayproductions.net>
>
> Is this the "standard" way to make a nonblocking Socket in Ruby?
> 
> require "socket"
> require "fcntl"
> 
> server = TCPServer.new(...)
> server.fcntl(Fcntl::F_SETFL, Fcntl::O_NONBLOCK)
> 
> __END__
> 
> Will that work on Unix and Windows?

As far as I know it's the "standard" way (but that
just means it's the only way I know of. :)

It doesn't work on Windows.  :(

I've ended up tacking on: ... if defined? Fcntl::O_NONBLOCK
onto the fcntl() line so that my scripts still run on
windows, even though they may block inappropriately.

Blocking I/O issues have been a thorny issue for me in
trying to write cross-platform network applications in
Ruby.

> If I accept() a connection from that, will the connecting socket be  
> nonblocking as well?

I seem to recall discussion of a patch to fix something
related to nonblocking I/O and accept() within the last
year or so... but I could be wrong... (I couldn't find
it with Google.)

I tend to re-issue the nonblock fcntl() call before 
every socket operation I perform.

Even so, I *still* hit this timeout occasionally:

  if select([sock], nil, nil, UDP_RECV_TIMEOUT)
    begin
      timeout(UDP_RECV_TIMEOUT) {
        sock.fcntl(Fcntl::F_SETFL, Fcntl::O_NONBLOCK) if defined? Fcntl::O_NONBLOCK
        resp = sock.recvfrom(65536)
      }
    rescue Timeout::Error
      $stderr.puts "Timeout::Error in sock.recvfrom !"
    end
  end

...Since select() said data was ready, AND since I'm
requesting a nonblocking operation... I have no idea
why #recvfrom sometimes hangs.  It used to totally hang
my program (on linux), indefinitely, about once a day,
until I added the timeout().


Regards,

Bill