Bug #496: DRb.start_service(nil) is very slow

• Status: Closed
• Assignee: seki (Masatoshi Seki)
• Target version: 1.9.2
• ruby -v: -

[hongli (Hongli Lai)]

=begin
On some systems - such as mine - DRB.start_service(nil) is very slow. This is caused by the fact that DRb.open_server calls TCPServer.open(nil, 0).addr[1]. On my system, this takes about 3 seconds, and during those 3 seconds there is 0% CPU usage.

I suspect it has got something to do with the fact that retrieving the port of a server socket that's bound to 0.0.0.0 is for some unknown reason very slow.

The problem can be fixed by replacing the following line in drb.rb

uri = 'druby://:0' unless uri

with:

uri = 'druby://localhost:0' unless uri

This does not violate DRb.start_service's contract, because a nil indicates that it will bind to the default local host name.

The following monkeypatch works around the issue:

module DRb
class << self
alias orig_start_service start_service
end

 def self.start_service(uri = nil, front = nil, config = nil)
   if uri.nil?
     orig_start_service("druby://localhost:0", front, config)
   else
     orig_start_service(uri, front, config)
   end
 end

end
=end

[candlerb (Brian Candler)]

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I suspect a DNS/hostname resolution problem on your system.

Looking at 1.8.6p114, notice that DRbTCPSocket.getservername first calls Socket.gethostname to get the hostname, then calls Socket.gethostbyname which does both forward and reverse name resolution, presumably to map to a "canonical" name. Then DRbTCPSocket.open_server_inaddr_any also calls Socket.getaddrinfo, although it discards the results apart from using them to decide whether to bind to IPv4, IPv6, or both.

Try the following in irb - how long does each step take?

{{{
require 'socket'
h1 = Socket.gethostname
h2 = Socket.gethostbyname(h1)[0]
Socket.getaddrinfo(h2, nil, Socket::AF_UNSPEC, Socket::SOCK_STREAM, 0, Socket::AI_PASSIVE)
}}}

If one of these steps is slow, you may be able to solve the problem by adding an entry in /etc/resolv.conf to map your hostname to your primary interface IP.

=end

[hongli (Hongli Lai)]

=begin
All of those steps finish instantaneously.

I'm on Ubuntu 8.04.
=end

[candlerb (Brian Candler)]

=begin
OK, how about this:

require 'socket'
t = TCPServer.new("", nil)
t.addr
t.addr

Socket.do_not_reverse_lookup=true
t.addr

On my machine, the first 't.addr' invocations take about 5 seconds. The last one is instant. I believe this is because of the delay looking up 0.0.0.0 in the DNS.

=end

[hongli (Hongli Lai)]

=begin
The last t.addr is instant for me as well.
=end

[hongli (Hongli Lai)]

=begin
Any update on this? Is my proposed fix acceptable?
=end

[rogerdpack (Roger Pack)]

=begin
Sounds like the problem is that
require 'socket'
t = TCPServer.new("", nil)
t.addr

is slow, is that the root of the problem?
-=r
=end

[shyouhei (Shyouhei Urabe)]

• Assignee set to seki (Masatoshi Seki)

=begin

=end

[marcandre (Marc-Andre Lafortune)]

• Category set to lib
• ruby -v set to -

=begin

=end

[mame (Yusuke Endoh)]

• Status changed from Open to Feedback
• Target version set to 1.9.2

=begin
Hi,

I cannot reproduce the issue with trunk on Linux.
Does this still reproduce?
Could you elaborate your platform and network configuration?

--
Yusuke Endoh [e-mail]
=end

[rogerdpack (Roger Pack)]

=begin
This might be fixed now, since Socket.do_not_reverse_lookup defaults to true now in trunk (maybe somebody should note that in the NEWS?)
Thanks.
-rp
=end

[mame (Yusuke Endoh)]

• Status changed from Feedback to Closed

=begin

=end