Give Tensor a trivial (for now) metaclass _TensorMeta (#56147)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56147
This is support of #55686, you can see the broader context of the metaclass in
a more complete PR #56017. The short story is that in the future I want to
give Tensor a non-trivial metaclass, so to derisk the change first I give it a
trivial metaclass to shake out any bugs that might be caused by it. The
metaclass shouldn't have any performance impact on Tensor as it only gets
invoked upon subclass creation.
By the way, it was totally not documented how to create metaclasses in the Python
C API, and it took a good bit of trial error to figure it out (and the answer is
now immortalized in https://stackoverflow.com/q/67077317/23845 -- the things
that I got wrong in earlier versions of the PR included setting tp_basicsize
incorrectly, incorrectly setting Py_TPFLAGS_HAVE_GC on the metaclass--you want
to leave it unset so that it inherits, and determining that tp_init is what
actually gets called when you construct a class, not tp_call as another
not-to-be-named StackOverflow question suggests).
Aside: Ordinarily, adding a metaclass to a class is a user visible change, as
it means that it is no longer valid to mixin another class with a different
metaclass. However, because _C._TensorBase is a C extension object, it will
typically conflict with most other metaclasses, so this is not BC breaking.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: H-Huang
Differential Revision: D28028747
Pulled By: ezyang
fbshipit-source-id: c1e35a986aeb3db540c73d188f53dce951eeed33
