This is a good idea, IMHO. I had a similar PR but Mark's is more elegant than mine.

🤖 New build scheduled with the buildbot fleet by @markshannon for commit 8aa20f2 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F132280%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

Initial performance numbers are a bit down. 0.2% - 1.6% slower.

I'm testing another branch that adds PyThreadState * as a parameter to _PyDealloc, which might reduce the impact.

With faster recursion checks, performance is mixed but no worse overall:

• Linux ARM: 0.4% slower
• Linux x86: 1.5% slower
• Windows x86: 0.9% faster
• Mac (ARM): 3.8% faster

Although the 1.5% slowdown on linux x86 is concerning.

I also tried passing in the thread state as a parameter to _Py_Dealloc which is a much larger change. Results were a bit worse than this PR:

• Linux ARM: no change
• Linux x86: 1.3% slower
• Windows x86: 1.3% slower
• Mac (ARM): 3.9% faster

Maybe perf will be better with just one additional if for a decref that is not a container. So you have an implementation of decref for containers, and do one if to decide whether to apply it or stay with the current one.

Maybe perf will be better with just one additional if for a decref that is not a container. So you have an implementation of decref for containers, and do one if to decide whether to apply it or stay with the current one.

Do you mean a test in Py_DECREF or in Py_Dealloc?
We really want to avoid adding more branches to Py_DECREF as Py_DECREF is inlined in so many places.

Adding a branch in Py_Dealloc would save the stack checks, but those are cheap. Getting the "margin" is a load, subtract and shift.

Testing for collections is more expensive. PyObject_IS_GC does three loads, two of which are dependent on the first.

Maybe perf will be better with just one additional if for a decref that is not a container. So you have an implementation of decref for containers, and do one if to decide whether to apply it or stay with the current one.

Do you mean a test in Py_DECREF or in Py_Dealloc?

Sorry, yeah, dealloc. Maybe not worth it.

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x RHEL8 3.x (tier-3) has failed when building commit 44e4c47.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/509/builds/9127) and take a look at the build logs.
4. Check if the failure is related to this commit (44e4c47) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/509/builds/9127

Failed tests:

• test_functools

Failed subtests:

• test_async_global_awaited_by - test.test_external_inspection.TestGetStackTrace.test_async_global_awaited_by

Summary of the results of the build (if available):

==

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-rhel8-s390x/build/Lib/test/test_external_inspection.py", line 531, in test_async_global_awaited_by
    self.assertEqual([[['echo_client_spam'], 'echo client spam', [[['main'], 'Task-1', []]]]], entries[-1][1])
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Lists differ: [[['echo_client_spam'], 'echo client spam', [[['main'], 'Task-1', []]]]] != []

Hi! The buildbot s390x RHEL8 3.x (tier-3) has failed when building commit 44e4c47.

test_recursive_pickle (test.test_functools.TestPartialPy.test_recursive_pickle) ...

Objects/classobject.c:247: _PyObject_GC_UNTRACK: Assertion "_PyObject_GC_IS_TRACKED(((PyObject*)(op)))" failed: object not tracked by the garbage collector
Enable tracemalloc to get the memory block allocation traceback

object address  : 0x3ffae27c8f0
object refcount : 0
object type     : 0x1669768
object type name: method
object repr     : <refcnt 0 at 0x3ffae27c8f0>

Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: initialized

Current thread 0x000003ffb6177270 [python] (most recent call first):
  File "/home/buildbot/buildarea/3.x.cstratak-rhel8-s390x/build/Lib/test/test_functools.py", line 420 in test_recursive_pickle
  (...)

I wrote #133199 to fix test_functools.