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comp.lang.ruby

UDP select()/recvfrom() delay under Windows?

David Holroyd

5/23/2005 8:23:00 PM

I have the following snippet of code in a UDP client I'm knocking
together:

def await_packet(timeout)
packet = @recv_queue.shift
return packet unless packet.nil?
read_fds = [@sock]
mylog("selecting..")
return nil unless (fds = select(read_fds, nil, nil, timeout))
selected_read_fds, selected_write_fds, selected_error_fds = fds
return nil unless selected_read_fds.include?(@sock)
mylog("recvfroming..")
data, from = @sock.recvfrom(MAX_SIZE)
mylog("..done recvfroming")
frame = NA::read_server_frame(ReadBuffer.new(data))
# TODO: filter stray ACKs?
frame
end


When I run my test code in ruby 1.8.2 (2004-12-25) [i386-mswin32], I
see, for example:

C:\na>ruby -w client_test.rb
1116865503.777 NA::PhoneSocket: selecting..
1116865503.777 NA::PhoneSocket: recvfroming..
1116865518.769 NA::PhoneSocket: ..done recvfroming
1116865518.779 NA::PhoneSocket: selecting..
1116865518.779 NA::PhoneSocket: recvfroming..
1116865538.287 NA::PhoneSocket: ..done recvfroming

I notice that there is a gap of some several seconds between select()
completing, and recvfrom() completing -- I expected that, since select()
reports data can be read, recvfrom() should not block. Am I wrong?

Also, I am fairly confident that there *is* data that could be read
immediately, as I can see packets arriving (in Ethereal, running on the
same machine as the above Ruby code).


Any help (even a reply that this is off-topic, and that I don't
understand socket programming) much appreciated.

dave

--
http://david.holr...
3 Answers

Ville Mattila

5/24/2005 5:05:00 AM

0

David Holroyd <ruby-talk@badgers-in-foil.co.uk> writes:
> When I run my test code in ruby 1.8.2 (2004-12-25) [i386-mswin32], I
> see, for example:
>
>
> I notice that there is a gap of some several seconds between select()
> completing, and recvfrom() completing -- I expected that, since select()
> reports data can be read, recvfrom() should not block. Am I wrong?
>
> Also, I am fairly confident that there *is* data that could be read
> immediately, as I can see packets arriving (in Ethereal, running on the
> same machine as the above Ruby code).
>
>
> Any help (even a reply that this is off-topic, and that I don't
> understand socket programming) much appreciated.

I think this will be fixed in 1.8.3 so you could try it. There is a 1.8.3rc1
available at www.ruby-lang.org. You have to compile it your self though.

- Ville

David Holroyd

5/24/2005 9:16:00 AM

0

On Tue, May 24, 2005 at 02:05:17PM +0900, Ville Mattila wrote:
> David Holroyd <ruby-talk@badgers-in-foil.co.uk> writes:
> > When I run my test code in ruby 1.8.2 (2004-12-25) [i386-mswin32], I
> > see, for example:
> >
> >
> > I notice that there is a gap of some several seconds between select()
> > completing, and recvfrom() completing -- I expected that, since select()
> > reports data can be read, recvfrom() should not block. Am I wrong?
>
> I think this will be fixed in 1.8.3 so you could try it. There is a 1.8.3rc1
> available at www.ruby-lang.org. You have to compile it your self though.

I don't have MSVC++, so I downloaded ruby-1.8.3-preview1-i386-mswin32.zip
from http://www.garbagecollect.jp/ruby/mswin32/en/download/re...
and unpacked that over the top of the install directory created by
ruby182-15.exe.

Using ruby 1.8.3 (2005-05-12) [i386-mswin32], I still see recvfrom()
block for 4-5 seconds each time it's called.

Oddly, when I access the server off-site, using a tunnel, there's no
delay (i.e. when the Ruby program is configured to connect to the tunnel
endpoint on localhost, rather than directly to the server machine).


dave

--
http://david.holr...

David Holroyd

5/25/2005 10:02:00 AM

0

On Tue, May 24, 2005 at 06:16:05PM +0900, David Holroyd wrote:
> On Tue, May 24, 2005 at 02:05:17PM +0900, Ville Mattila wrote:
> > David Holroyd <ruby-talk@badgers-in-foil.co.uk> writes:
> > > I notice that there is a gap of some several seconds between
> > > select() completing, and recvfrom() completing -- I expected that,
> > > since select() reports data can be read, recvfrom() should not
> > > block. Am I wrong?
> >
> > I think this will be fixed in 1.8.3 so you could try it. There is a
> > 1.8.3rc1 available at www.ruby-lang.org. You have to compile it
> > your self though.

> Using ruby 1.8.3 (2005-05-12) [i386-mswin32], I still see recvfrom()
> block for 4-5 seconds each time it's called.
>
> Oddly, when I access the server off-site, using a tunnel, there's no
> delay (i.e. when the Ruby program is configured to connect to the tunnel
> endpoint on localhost, rather than directly to the server machine).

Thanks to the suggestion of Kent Sibilev in...

http://www.ruby-talk.org/cgi-bin/scat.rb/ruby/ruby-t...

...my app is now running much faster. Yay! :)


dave

--
http://david.holr...