From: chris guenther <chris_guenther@...>
Date: 2005-04-10T18:19:39+09:00
Subject: weird delay of UDP server (seems to be thread-scheduling issue)

Hi,

the UDP client/server progam below does not work as expected.
Given one input line ('df' see below) the server-thread does not (YET)
receive the UDP packet, although the client thread had sent it already.
ONLY after entering another bunch of empty lines (just hitting <ENTER>) the
receiver thread suddenly receives the packet.

It seems to me that the receiver thread is not scheduled at the time I
expect it to be scheduled (right after sending).

Can anyone throw some light on this issue ??

TIA,
Chris



#--=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=
#!/usr/bin/env ruby

require 'socket'
require 'time'

STDOUT.sync=true
$port = 4321
def now; Time.new.strftime('%H:%M:%S') ;end

sThread = Thread.start do
  puts "server : bound port #{$port} at #{now}\n"
  server = UDPSocket.open
  server.bind(nil, $port)
  loop { puts "#{server.recvfrom(1024)[0]}\treceived at #{now}" }
end

sock = UDPSocket.open
sock.connect('localhost', $port)
loop {
 print "--> "
 case line = readline.chomp
 when /^q/
  exit 0
 else
  if line.length>0   ### Dont send EMPTY LINES
   payload="'#{line}'\tsent at #{now}"
   sock.send(payload, 0)
   puts "sent ::\t#{payload}"
  end
 end
}

#--=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=

############ trace of execution ############

# ruby -v -w udp_test.rb
ruby 1.8.2 (2004-12-25) [i386-mswin32]
server : bound port 4321 at 11:01:02
--> df
sent :: 'df'    sent at 11:01:05
-->
-->
-->
-->
-->
-->
-->
-->
-->
--> 'df'        sent at 11:01:05        received at 11:01:09