Eryk Sun <[email protected]> added the comment:
> `data_as` method which has the desired behavior: "The returned
> pointer will keep a reference to the array."
I don't think it's the desired behavior at all. data_as() sets an _arr
attribute of which ctypes isn't aware. It should cast the address to the given
type and manually set the array reference in the _objects dict, which ctypes
will automatically carry forward in all instances of aggregate types (structs
and arrays) that reference the numpy array. For example:
>>> p = a.ctypes.data_as(ptype)
>>> p._objects['1'] = a
Adding p to an array carries its _objects dict forward:
>>> ptarr = (ptype * 1)(p)
>>> ptarr._objects['0']['1'] is a
True
If the returned pointer is cast() again, then bpo-12836 is an issue. For
example:
>>> p2 = ctypes.cast(p, ctypes.c_void_p)
>>> p._objects is p2._objects
True
>>> for k in p._objects:
... if p._objects[k] is p:
... print('circular reference')
...
circular reference
That needs to be fixed. But relying on _arr instead of correctly integrating
with ctypes isn't a good idea, IMO. Work around the actual bug instead of
introducing behavior that risks crashing just for the sake of resolving an
uncommon circular reference problem.
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Python tracker <[email protected]>
<https://bugs.python.org/issue41883>
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