Clarification on refcounting behavior of object handlers/get_gc

Description

When implementing https://github.com/mongodb/mongo-php-driver/pull/1850, I have encountered some strange refcounting behavior within the garbage collector; specifically, when working with the hashtable returned by get_gc in https://github.com/php/php-src/blob/master/Zend/zend_gc.c#L892 and https://github.com/php/php-src/blob/master/Zend/zend_gc.c#L1516 the refcount is incremented and then seemingly not decremented again (leading to the leaks I'm fighting in https://github.com/mongodb/mongo-php-driver/pull/1850), but in https://github.com/php/php-src/blob/master/Zend/zend_gc.c#L1068, the refcount is decremented correctly.

This brings the question: what should be the refcount of the hashtables returned by get_gc, get_properties_for (in all of the various modes), get_properties, get_debug_info, and all other object handlers?

This detail is not documented anywhere, and specifically for get_gc, it's especially not clear given that returning a refcount of 0 would cause a negative refcount in one place, and returning 1 causes a leak in other two places (though that may be due to an issue in my implementation in the https://github.com/mongodb/mongo-php-driver/pull/1850 PR, though it's not immediately obvious what it is to me).

It would be super nice to have it documented at least inside of the source code as comments too...

PHP Version

8.4.10

Operating System

No response

Start with the referenced sections of Zend/zend_gc.c around lines 892, 1068, and 1516, then compare the get_gc behavior with get_properties_for, get_properties, and get_debug_info. Review the linked mongo-php-driver pull request for the reported leaks; done means the expected refcount ownership for each handler is established and documented in the relevant source comments.