gh-152666: Avoid reference counting of code objects

[brijkapadia]

Functions keep a list of past code objects so that a frame only needs borrowed references to them.

• Issue: Avoid refcounting on code objects during frame creation/destruction #152666

[markshannon]

The implementation of the old codes list looks good.
I'm wondering if the behavior, not the implementation, could be tested (or is it already?)

Also, can you make f_executable a PyObject * and always borrow it, to minimize overhead?

[markshannon]

This should be a borrowed reference for generators as well.
The function object still keeps the code object alive, regardless of whether it is a generator function or not.

[brijkapadia]

I'm not sure if there is a trivial way for a generator to hold onto a borrowed reference since for a generator g, you can always access the code object by doing g.gi_code. The function can get freed but the code object is still needed. See, for example, this test:

cpython/Lib/test/test_generators.py

Lines 116 to 135 in 4221ce7

	def test_generator_resurrect(self):
	# Test that a resurrected generator still has a valid gi_code
	resurrected = []
	# Resurrect a generator in a finalizer
	exec(textwrap.dedent("""
	def gen():
	try:
	yield
	except:
	resurrected.append(g)
	g = gen()
	next(g)
	"""), {"resurrected": resurrected})
	support.gc_collect()
	self.assertEqual(len(resurrected), 1)
	self.assertIsInstance(resurrected[0].gi_code, types.CodeType)

[markshannon]

The old codes list is an implementation detail.
Would it be possible to check the behavior rather than the implementation?

Specifically, test that:

• reassigning the code object for a running function still works
• reassigning many code objects doesn't leak memory

[bedevere-app]

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