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Date: Wed, 2 Dec 2015 20:53:43 +0000
From: Eric Wong <e@80x24.org>
To: =?utf-8?B?5LyK6Jek5rSL5Lmf?= <hiroyan@gmail.com>
Cc: mogilefs-client-public@bogomips.org
Subject: Re: JRuby 9.0.4.0 + mogilefs-client
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伊藤洋也 <hiroyan@gmail.com> wrote:
> The same problem has been issued and discussed on GitHub jruby/jruby
> https://github.com/jruby/jruby/issues/1694, but not been resolved yet.
> 
> It might not be appropriate to ask you about this problem since it
> does not seem to be the problem of mogilfs-client but of jruby, but do
> you have any ideas?

I can help with nearly any userspace <-> kernel issues on GNU/Linux
and maybe FreeBSD.  However, I don't know C++ or Java at all,
so I'm not sure what your JVM or JRuby is doing...

Under Linux, it would be helpful to compare strace output between
C Ruby and JRuby with the test script below (and variations from
making adjustments where I left "XXX" comments).

Does retrying connect_nonblock on EINPROGRESS/EALREADY help?
In other words, something like this:

require 'socket'
require 'io/wait'

sock = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
addr = Socket.sockaddr_in(7001, '127.0.0.1')
begin
  # XXX it would be worth trying sock.connect(addr) instead
  # and compare strace output between C Ruby and JRuby, too
  sock.connect_nonblock(addr)
rescue Errno::EINPROGRESS, Errno::EALREADY => e
  warn "waiting on #{e.class}"

  # XXX Maybe you need to comment out this line on JRuby?
  # Ideally you wouldn't need the timeout arg for wait_writable
  sock.wait_writable(0.001)

  retry
rescue Errno::EISCONN
  warn "Success!"
end

unless sock.wait_writable(5)
  raise 'MogileFS::Timeout, socket connect timeout'
end
----------------

And based on the comments on that ticket, it might be a problem
with the JVM or JRuby mishandling the issue...

Regardless of whether I can help, thank you for documenting the
issue publically.