On 17 Feb 2014 06:12, "Serhiy Storchaka"
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.
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