Bug report

I'm been hunting a memory leak in pydantic and I keep seeing_abc_subclasscheck popping up in the memray flamegraph.

Locally I've seen memray report that_abc_subclasscheck is using 2.8GB of memory in some cases!

I can't get anything that bad in a minimal example, but I have the following:

fromabcimportABCMetafromdatetimeimportdatetimeclassMyMetaclass(ABCMeta):passclassMyClass(metaclass=MyMetaclass):passdefmain():classFoobar(MyClass):passassertissubclass(Foobar,MyClass)assertnotissubclass(int,MyClass)assertnotissubclass(str,MyClass)assertnotissubclass(datetime,MyClass)t=type('A', (), {})assertnotissubclass(t,MyClass)if__name__=='__main__':importos,psutilprocess=psutil.Process(os.getpid())mb=1024*1024last=0foriinrange(5_000):main()# mem = process.memory_info().rss# print(f'{i + 1:>4d} {mem / mb:8.2f}MB {(mem - last) / mb:+8.2f}MB | {"━" * int(mem / 8_000_000)}')# last = mem

A few things to note:

• the commented out last few lines print current memory and change in memory over time
• I'm not sure exactly whichissubclass calls are necessary, certainly I don't see a rise in memory with just the last one
• some memory drops (presumably related to clearing the abc caches?) is happening, but overall memory is increasing
• The performance ofissubclass on an abc is very poor indeed - this script takes 14seconds, if i switchABCMeta totype it takes 121ms!

Your environment

• Python 3.10.0 installed with venv
• Ubuntu 21.10

Linked PRs

• gh-92810: Reduce memory usage by ABCMeta.__subclasscheck__ #131914