[Python-Dev] PyWeakref_GetObject() borrows its reference from... whom?

[Larry Hastings]

By the way, just to finish playing this new fun game "Who'd I Borrow 
This Reference From?":


On 10/10/2016 11:45 AM, Chris Angelico wrote:
> On Mon, Oct 10, 2016 at 8:35 PM, Larry Hastings <larry at hastings.org> wrote:
>> I bet for every other spot in the API I can tell you from
>> whom you're borrowing the reference.
> Okay. Here's a test:
>
> PyObject* PyList_GetItem(PyObject *list, Py_ssize_t index)
> Return value: Borrowed reference.
>
> Presumably you own a reference to the list itself before you call
> this, and the list has a reference to its items. But suppose another
> thread clear()s the list immediately after you call this; whose
> reference are you borrowing now? The list's is gone.

As you say: you've borrowed the reference from the list.  With the GIL 
this is safe.  After the Gilectomy it's not always safe.  It *can* be: 
for example, if you allocated the list locally in the current thread, 
and it hasn't escaped the thread yet, you can assert that in this case 
reference will never go away on you.  But in general this is an API that 
has to change for the Gilectomy.


//arry/
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