On Sat, Mar 31, 2012 at 7:45 PM, R. David Murray <rdmur...@bitdance.com>wrote:
> On Sun, 01 Apr 2012 03:03:13 +1000, Nick Coghlan <ncogh...@gmail.com> > wrote: > > On Sun, Apr 1, 2012 at 2:09 AM, Guido van Rossum <gu...@python.org> > wrote: > > > Here's a different puzzle. Has anyone written a demo yet that provokes > > > this RuntimeError, without cheating? (Cheating would be to mutate the > > > dict from *inside* the __eq__ or __hash__ method.) If you're serious > > > about revisiting this, I'd like to see at least one example of a > > > program that is broken by the change. Otherwise I think the status quo > > > in the 3.3 repo should prevail -- I don't want to be stymied by > > > superstition. > > > > I attached an attempt to *deliberately* break the new behaviour to the > > tracker issue. It isn't actually breaking for me, so I'd like other > > folks to look at it to see if I missed something in my implementation, > > of if it's just genuinely that hard to induce the necessary bad timing > > of a preemptive thread switch. > > Thanks, Nick. It looks reasonable to me, but I've only given it a quick > look so far (I'll try to think about it more deeply later today). > > If it is indeed hard to provoke, then I'm fine with leaving the > RuntimeError as a signal that the application needs to add some locking. > My concern was that we'd have working production code that would start > breaking. If it takes a *lot* of threads or a *lot* of mutation to > trigger it, then it is going to be a lot less likely to happen anyway, > since such programs are going to be much more careful about locking > anyway. > > --David > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/fijall%40gmail.com > Hm I might be missing something, but if you have multiple threads accessing a dict, already this program: http://paste.pocoo.org/show/575776/ raises RuntimeError. You'll get slightly more obscure cases than changing a size raise RuntimeError during iteration under PyPy. As far as I understood, if you're mutating while iterating, you *can* get a runtime error. This does not even have a custom __eq__ or __hash__. Are you never iterating over dicts? Cheers, fijal
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