[Zope] Zope hanging (poss. threads-related)

[Marcus Collins]

Apologies for the imposing subject line...

Briefly, since increasing the NUMBER_OF_THREADS that Zope uses from the
default (4) to 20, Zope has been hanging randomly. A request will be sent
off to Zope (whether through apache with mod_pcgi, or directly through
ZServer), but the request is never served up, and Z2.log shows no record of
it. No additional CPU is taken by the python process.

Environment:
 Zope 2.1.3 (source release)
 python 1.5.2
 GCC 2.7.2.3
 FreeBSD 3.3-RELEASE

The problem was reproducible on pages with framesets, where some of the
frame documents are loaded, and one is omitted. It occurs when viewing the
management interface, for example (manage_main is displayed, but
manage_workspace is not). It seems that only one thread hangs, since other
requests continue to be served. Not only frameset pages were affected,
though only on frameset pages did the hanging consistently occur.

This behaviour was exhibited under minimal load (one or two users), and
ceased when I reverted to 4 threads and restarted Zope.

Our development machine, running 2.1.4 source, had no such problems when
running Zope with 20 threads. I don't recall any drastic changes or checkins
between 2.1.3 and 2.1.4, though... (that was basically the /REQUEST
traversal security fix)

I'll be installing Zope 2.1.6, and try to approximate the the same
conditions, but since this is a live machine, it's going to be tricky to
find a window of time to perform the switch-over...

Anyone out there with some ideas as to the root cause of these hangings, or
with similar tales to tell?

TIA,

-- Marcus