zope.copy cannot handle BTreeContainers with more than ~7800 items

[mgedmin]

What I did:

N_ITEMS = 8000   # 7761 was the smallest value that raised RuntimeError


def test_clone_large_btree_container():
    obj = BTreeContainer()
    for n in range(N_ITEMS):
        obj[str(n)] = None
    zope.copy.clone(obj)   # raises RuntimeError: maximum recursion depth exceeded

What I expect to happen:

Copy the container

What actually happened:

Traceback (most recent call last):
  File "/home/mg/src/zope-copy-stack-overflow-error/repro.py", line 16, in <module>
    test_clone_large_btree_container()
  File "/home/mg/src/zope-copy-stack-overflow-error/repro.py", line 12, in test_clone_large_btree_container
    zope.copy.clone(obj)
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/copy/__init__.py", line 31, in clone
    pickler.dump(obj)
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/copy/__init__.py", line 85, in id
    hook = interfaces.ICopyHook(obj, None)
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/component/_api.py", line 152, in adapter_hook
    return sitemanager.queryAdapter(object, interface, name, default)
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/interface/registry.py", line 354, in queryAdapter
    return self.adapters.queryAdapter(object, interface, name, default)
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/proxy/__init__.py", line 573, in <lambda>
    return property(lambda self: func.__get__(self))
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/container/contained.py", line 932, in __get__
    for iface in list(provided):
  File "/home/mg/src/zope-copy-stack-overflow-error/.tox/py39/lib/python3.9/site-packages/zope/interface/interface.py", line 516, in interfaces
    for base in self.__bases__:
RecursionError: maximum recursion depth exceeded

What version of Python and Zope/Addons I am using:

Python on Linux (Python 3.9 on Ubuntu 22.10, among other combinations)

zope.container 4.10, zope.copy 4.3

[mgedmin]

Probably relevant upstream issue: python/cpython#47369.

If I do import pickle; pickle.dumps(obj) I get the same runtime error on this BTreeContainer.

(Since I wondered and looked it up, here's a factlet: zope.copy does not use zodbpickle for this, it uses the stdlib pickle.)

[mgedmin]

A OOBucket holds up to 20 items by default. The buckets in an OOBTree constitue a singly-linked list, with the OOBTree itself holding additional direct references to all the buckets. Here's a tree with 100 items:

An OOBTree with 8000 items has a bit over 500 buckets, depending on the order of insertion. sys.getrecursionlimit() is 1000 by default. If pickle uses up two stack frames per object, a depth-first graph traversal starting from the first bucket will hit the limit.