[Python-3000] threading, part 2 (original) (raw)

Guido van Rossum guido at python.org
Thu Aug 10 06:14:03 CEST 2006

On 8/9/06, Tim Peters <tim.peters at gmail.com> wrote:

[back and forth on PyThreadStateSetAsyncExc()]

[Tim] >> Guido, do you have any idea now what the "number greater than one" >> business is about? >> ... >> My impression has been that it would be an internal logic error if we >> ever saw this count exceed 1. [Guido] > Right, I think that's it. I guess I was in a grumpy mood when I wrote > this I forgot that we talked about this close to two years ago: http://www.python.org/sf/1069160 As comments there say, it's still the case that it's clearly possible to provoke this into deadlocking (but unlikely if you're not deliberately trying to). > (and Just & Alex never ended up using it!). They spoke for themselves on this matter in that bug report ;-) >> While I'm at it, I expect: >> >> PyCLEAR(p->asyncexc); >> PyXINCREF(exc); >> p->asyncexc = exc; >> >> is better written: >> >> PyXINCREF(exc); >> PyCLEAR(p->asyncexc); >> p->asyncexc = exc; >> >> for the same reason one should always incref B before decrefing A in >> >> A = B >> >> ... > That reason that A and B might already be the same object, right? Right, or that B's only owned reference is on a chain only reachable from A, and in either case A's incoming refcount is 1. The suggested deadlock-avoiding rewrite in the patch comment addresses that too.

So why didn't we check that in?

...

>>> I'm +0 on [exposing] this [from Python]. >> Me too, although it won't stay that simple, and I'm clear as mud on >> how implementations other than CPython could implement this. > Another good reason to keep it accessible from the C API only. Now I'm > -0 on adding it. I suggest that if someone really wants this > accessible from Python, they should research how Jython, IronPython, > PyPy and Stackless could handle this, and report their research in a > PEP. As a full-blown language feature, I'm -1 unless that work is done first. I'm still +0 on adding it to CPython if it's given a leading-underscore name and docs to make clear that it's a CPython-specific hack that may never work under any other implementation.

Fine with me then. In 2.5? 2.6? Or py3k? (This is the py3k list.)

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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