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

[Chris Angelico]

On Tue, Oct 11, 2016 at 9:52 AM, MRAB <python at mrabarnett.plus.com> wrote:
>> Also, I don't know when it would ever be safe to release the "memory
>> deallocation lock".  Just because it's safe for your thread doesn't mean
>> it's safe for another thread.  And if you do it on a thread-by-thread
>> basis, in the above example it might be safe from thread B's perspective
>> to release its "memory deallocation lock", but as illustrated that can
>> have an effect on thread A.
>>
> The deallocation lock could be a counter. Doomed objects would be
> collectable when it's zero.

Yeah, which is why I described it as a "guard". As long as you have
atomic increment/decrement (ie if two threads simultaneously try to
increment it, it WILL go up by two), it should be fine. Well, that
part should, anyway.

ChrisA