[Zope-dev] Problem with zope.sendmail in Python >= 2.5.1

[Chris McDonough]

FWIW, we forked zope.sendmail a while back (with the intent of eventually 
merging these changes back upstream) as "repoze.sendmail".  It does not use any 
thread to do queue processing.  Instead, a separate process can be run to handle 
queue processing.

This is being actively maintained.

http://repoze.org/viewcvs/repoze.sendmail/trunk/README.txt?rev=3688&view=markup

On 9/3/09 10:07 PM, Gary Poster wrote:
> Hi all.  One of the contributors to the Launchpad project has
> identified a problem with zope.sendmail and thread changes in Python
>   >= 2.5.1.  Here is his description:
>
> """
> Description of the situation:
>
> Prior to Python 2.5.1, the atexit handlers were executed when the
> *main* thread exits. However,http://bugs.python.org/issue1566280 was
> then filed, the essence of which is that the atexit handlers could
> tear down cross-thread resources that were still in use by other
> threads.
>
> For this reason, the shutdown procedure was modified in Python 2.5.1 -
> now, when the main thread exits, it first makes a private call to
> threading._shutdown(), which waits until all non-daemon threads have
> exited, and *only then* proceeds to run the atexit handlers.
>
> Herein lies the problem. zope.sendmail.delivery.QueueProcessorThread
> attempts to use atexit to notify itself when it should shut down.
> However, the Python runtime>= 2.5.1 will wait for the
> QueueProcessorThread to exit before it calls the atexit handlers!
>
> Potential solutions:
>
> (1) To gain behaviour most similar to earlier Python versions, an evil
> monkeypatch into Python internals like this: http://bazaar.launchpad.net/~maxb/zope3/launchpad-3.4-py2.5/revision/9works
> .
>
> (2) Make the QueueProcessorThread a daemon thread. It will be
> terminated without notification when the interpreter exits, but the
> current QueueProcessorThread does not attempt to ensure its queue is
> completely flushed before shutdown anyway, so that should not matter.
>
> I will attach a small Python demo program useful for illustrating and
> exploring the issue.
> """
>
> You can see the bug report, and his demo program, here:
>
> https://bugs.edge.launchpad.net/zope3/+bug/413335
>
> I wasn't going to send this until I had investigated this myself, but
> I have been taking too long and thought I'd at least send this out to
> see if anyone has any thoughts.  Otherwise, I'll look into it ASAP and
> report back.
>
> Thanks
>
> Gary
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