Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!goblin2!goblin.stu.neva.ru!newsfeed.xs4all.nl!newsfeed1a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
From: Felix Yan <felixonmars@gmail.com>
To: python-list@python.org
Subject: Re: Thread._stop() behavior changed in Python 3.4
Date: Tue, 18 Mar 2014 01:59:52 +0800
User-Agent: KMail/4.12.3 (Linux/3.13.6-1-uksm; KDE/4.12.3; x86_64; ; )
In-Reply-To: <loom.20140317T182601-605@post.gmane.org>
References: <279038900.uDlbjECTej@felix-arch> <loom.20140317T182601-605@post.gmane.org>
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="nextPart1544915.Zz97aImPkM"; micalg="pgp-sha1"; protocol="application/pgp-signature"
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.8211.1395079205.18130.python-list@python.org>
Lines: 91
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:68444


--nextPart1544915.Zz97aImPkM
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="utf-8"

On Monday, March 17, 2014 17:33:09 Antoine Pitrou wrote:
> Hi,
> 
> Felix Yan <felixonmars <at> gmail.com> writes:
> > A minimized snippet to reproduce:
> > 
> > #!/usr/bin/python
> > import threading
> > 
> > def stale():
> >     import time
> >     time.sleep(1000)
> > 
> > t = threading.Thread(target=stale)
> > t.start()
> > t._stop()
> > 
> > This works correctly with Python 3.3, the program exits immediately after
> > t._stop() called, and no exception was raised.
> 
> Basically what you are doing is abusing a private method because you want
> to make the thread daemonic after it was started (a daemonic thread is
> not waited for at interpreter exit). Please do note one thing: the _stop()
> method does *not* actually stop the thread; it just marks it stopped, but
> the underlying OS thread continues to run (and may indeed continue to
> execute Python code until the interpreter exits).
> 
> So the obvious "solution" here is to mark the thread daemonic before
> starting it.
> 
> A possible related improvement would be to relax the contraints on
> Thread.daemon to allow setting the flag on a running thread?
> 
> That said, daemon threads (or abuse of the _stop() method as you did) can
> lead to instabilities and oddities as some code will continue executing
> while the interpreter starts shutting down. This has been improved but
> perhaps not totally solved in recent interpreter versions. A fully correct
> solution would involve gracefully telling the thread to shut down, via a
> boolean flag, an Event, a file descriptor or any other means.
> 
> (if you are interested in this, please open a new issue at
> http://bugs.python.org)
> 
> Regards
> 
> Antoine.

Thanks for the detailed explanation!

Actually I didn't used _stop() myself either, but noticed the problem when 
trying to build paramiko against python 3.4.

Thanks especially for the tip that the threads may be still running - actually 
I didn't even think about this part!

For now I just skipped the test suites for paramiko to get the packaging done 
(since the test suites themselves are passed without a problem, just the test 
script made something wrong). I'll try to follow up the issue for paramiko :)

Regards,
Felix Yan
--nextPart1544915.Zz97aImPkM
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: This is a digitally signed message part.
Content-Transfer-Encoding: 7Bit

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.22 (GNU/Linux)
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=7G2g
-----END PGP SIGNATURE-----

--nextPart1544915.Zz97aImPkM--