[Python-Dev] Re: Thread safety of deques (original) (raw)

Michael Hudson mwh at python.net
Tue Jul 20 16:20:01 CEST 2004

"Moore, Paul" <Paul.Moore at atosorigin.com> writes:

From: Aahz

On Mon, Jul 19, 2004, Phillip J. Eby wrote:

However, anything that calls back into Python code isn't necessarily atomic, and in general, almost anything can call back into Python code. Yup. For example, the seemingly harmless dictionary item assignment can call back into Python for a custom type's hash and eq methods, so could it be that a thread switch could actually occur during this statement: foo[bar] = baz if 'bar' has such custom methods? Maybe I'm wrong, and the GIL is still held in such a case, but I'm not sure how. No, it isn't. Hmm. I think that makes the point fairly well - thread safety is subtle, and not to be taken lightly. Whether that was Raymond's point or mine, I'm less sure :-)

To be fair, you don't need threads to tickle very odd behaviour here -- check out vicious_descriptor_nonsense in test_descr or test_mutants or some stuff in test_sort. Threads just add that delicious air of unpredictability to the mix :-)

Cheers, mwh

-- To summarise the summary of the summary:- people are a problem. -- The Hitch-Hikers Guide to the Galaxy, Episode 12

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