On 10/10/2016 11:05 AM, Devin Jeanpierre wrote:
> > whose reference is it borrowing?
>
> I think this is a red herring sort of question. "borrowed" only means
> "unowned". But anyway, we borrowed from the weakref. (Borrowing from
> somebody doesn't imply they own a reference -- we can borrow from a
> borrowed reference, for example, and this is common.)
Huh? In all other circumstances, a "borrowed" reference is exactly
that: X has a reference, and you are relying on X's reference to keep
the object alive. Borrowing from a borrowed reference is simply a chain
of these; Z borrows from Y, Y borrows from X, and X is the original
person who did the incref. But you're borrowing from something
specific, somebody who the API guarantees has a legitimate reference on
the object and won't drop it while you're using it. I bet for every
other spot in the API I can tell you from whom you're borrowing the
reference.
In contrast, the "borrowed" reference returned by PyWeakRef_GetObject()
seems to be "borrowed" from some unspecified entity. The fact that the
object is live in Python directly implies that, yes, *somebody* must
have a reference, somewhere. But ISTM (and apparently you) that this is
relying on the GIL preventing that unknown other actor from dropping
their reference while you've borrow it. A guarantee that the
post-Gilectomy Python interpreter can no longer make!
In any case, I see nothing in the documentation that suggests "borrowed
only means unowned" as you suggest. In contrast, the documentation
seems to suggest that the metaphor is how I understood it; that when you
"borrow" a reference, there is another object who has a reference and
you're relying on their reference to keep the object alive.
https://docs.python.org/3.6/extending/extending.html#reference-counts
//arry/
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