On 17 Feb 2014 06:12, "Serhiy Storchaka" <storch...@gmail.com> wrote: > > 16.02.14 02:05, Nick Coghlan написав(ла): > >> It's also likely than many of these crashes could only be reproduced >> through incorrect usage of the C API. > > > Rather through queer or malicious usage of Python classes with strange code in __del__.
This change doesn't fix any of the known crashers in Lib/test/crashers, though - I applied the patch locally and checked. >> For example: >> >> Py_CLEAR_AND_SET >> Py_XCLEAR_AND_SET >> >> Such that Py_CLEAR and Py_XCLEAR are equivalent to: > > > There is no Py_XCLEAR. Py_CLEAR itself checks its argument for NULL (as Py_XDECREF and Py_XINCREF). And these names looks too cumbersome to me. > > >> While the name does suggest the macro will expand to: >> >> Py_CLEAR(target); >> target = value; >> >> which isn't quite accurate, it's close enough that people should still >> be able to understand what the operation does. > > > This is not just inaccurate, this is wrong. Py_REPLACE first assigns new value and then DECREF old value. The point is that people already know what Py_CLEAR does. This operation is like Py_CLEAR (the old reference is only removed *after* the pointer has been updated), except that the value it is being replaced with can be something other than NULL. If the replacement value *is* NULL, then the new operation is *exactly* equivalent to Py_CLEAR. Operations that do related things should ideally have related names. The point of my deliberately erroneous expansion is that it's an error a reader can make while still correctly understanding the *logic* of the code, even though they're missing a subtlety of the mechanics. > So it rather can be named as Py_SET_AND_DECREF, but of course this name looks ugly and confusing. An explicit name like Py_SET_AND_DECREF would also be reasonable. It's substantially less confusing than Py_REPLACE, as it is less ambiguous about whether or not the refcount on the new value is adjusted. Cheers, Nick. > > > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ncoghlan%40gmail.com
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