From: Bill Kelly <billk@...>
Date: 2004-08-26T18:27:08+09:00
Subject: Re: [BUG?] apparent hang (win32 and Linux), have stack trace

Hi again,

I wondered if I could check an assumption or two here...
I have a slightly tweaked version of the prior script,
which for whatever reason seems to hang even more quickly.
(Seconds to minutes....)
http://bwk.homeip.net/ftp/buffered-io-test4b.rb

I've recompiled ruby without optimization so I can see
what's going on in the debugger more easily.

One assumption I'd like to check, is whether a
(delay == DELAY_INFTY) select should *ever* occur in
rb_thread_schedule while my script is running.

I am thinking this should not occur, because my main
thread *only* ever sleeps in the following situation:

  begin
    alarm_th = Thread.start {
      sleep timeout_secs
      $global_signal.broadcast  # %%WAS: .signal
    }
    $global_mutex.synchronize {
      print "{"
      $global_signal.wait($global_mutex)
      print "}"
    }
  ensure
    alarm_th.kill if alarm_th and alarm_th.alive?
  end

...that is, my main thread only goes to sleep when
another thread has specifically been created with
a non-INFTY delay (sleep timeout_secs) in order to
wake my main thread up.  So, I'd think that there
should be no way to get a (delay == DELAY_INFTY) in
rb_thread_schedule.

...UNLESS... . . . The other assumption I'd like to
check:

My main thread also reads and writes to a socket:

  if select(nil, [$cl_sock], nil, 0)
    print "W"
    sent = $cl_sock.send(" #$frame ", 0)
  end

  if select([$cl_sock], nil, nil, 0)
    print "R"
    dat = $cl_sock.recv(65536)
  end

... my assumption here is that send/recv WILL NOT 
block, because select just told me the socket is
readable or writable.  (No other thread is touching
this socket.)


According to what I'm seeing in the debugger, what
is apparently happening is that I eventually get 
a (delay == DELAY_INFTY) select, and it waits 
forever.

Also - it would appear this hanging condition only
occurs when the main thread is in the:

      print "{"
->    $global_signal.wait($global_mutex)
      print "}"

...and never in the send/recv part of the code.

So it seems a (delay == DELAY_INFTY) is happening
there, when I think it shouldn't....  Am I wrong?


Thanks for your help,

Regards,

Bill