gh-142414: Remove singleton design pattern in Lib/concurrent/interpreters/_crossinterp.py.

Lib/concurrent/interpreters/_crossinterp.py

@@ -5,71 +5,7 @@ class ItemInterpreterDestroyed(Exception):
  """Raised when trying to get an item whose interpreter was destroyed."""
 
 
-class classonly:
- """A non-data descriptor that makes a value only visible on the class.
-
- This is like the "classmethod" builtin, but does not show up on
- instances of the class. It may be used as a decorator.
- """
-
- def __init__(self, value):
- self.value = value
- self.getter = classmethod(value).__get__
- self.name = None
-
- def __set_name__(self, cls, name):
- if self.name is not None:
- raise TypeError('already used')
- self.name = name
-
- def __get__(self, obj, cls):
- if obj is not None:
- raise AttributeError(self.name)
- # called on the class
- return self.getter(None, cls)
-
-
-class UnboundItem:
- """Represents a cross-interpreter item no longer bound to an interpreter.
-
- An item is unbound when the interpreter that added it to the
- cross-interpreter container is destroyed.
- """
-
- __slots__ = ()
-
- @classonly
- def singleton(cls, kind, module, name='UNBOUND'):
- doc = cls.__doc__
- if doc:
- doc = doc.replace(
- 'cross-interpreter container', kind,
- ).replace(
- 'cross-interpreter', kind,
- )
- subclass = type(
- f'Unbound{kind.capitalize()}Item',
- (cls,),
- {
- "_MODULE": module,
- "_NAME": name,
- "__doc__": doc,
- },
- )
- return object.__new__(subclass)
-
- _MODULE = __name__
- _NAME = 'UNBOUND'
-
- def __new__(cls):
- raise Exception(f'use {cls._MODULE}.{cls._NAME}')
-
- def __repr__(self):
- return f'{self._MODULE}.{self._NAME}'
-# return f'interpreters._queues.UNBOUND'
-
-
-UNBOUND = object.__new__(UnboundItem)
+UNBOUND = object()
 UNBOUND_ERROR = object()
 UNBOUND_REMOVE = object()
 

Lib/concurrent/interpreters/_queues.py

@@ -11,7 +11,7 @@
  QueueError, QueueNotFoundError,
 )
 from ._crossinterp import (
- UNBOUND_ERROR, UNBOUND_REMOVE,
+UNBOUND, UNBOUND_ERROR, UNBOUND_REMOVE,
 )
 
 __all__ = [
@@ -46,9 +46,6 @@ class ItemInterpreterDestroyed(QueueError,
 _PICKLED = 1
 
 
-UNBOUND = _crossinterp.UnboundItem.singleton('queue', __name__)
-
-
 def _serialize_unbound(unbound):
  if unbound is UNBOUND:
  unbound = _crossinterp.UNBOUND

Lib/test/support/channels.py

@@ -10,7 +10,7 @@
  ChannelEmptyError, ChannelNotEmptyError, # noqa: F401
 )
 from concurrent.interpreters._crossinterp import (
- UNBOUND_ERROR, UNBOUND_REMOVE,
+UNBOUND, UNBOUND_ERROR, UNBOUND_REMOVE,
 )
 
 
@@ -28,9 +28,6 @@ class ItemInterpreterDestroyed(ChannelError,
  """Raised from get() and get_nowait()."""
 
 
-UNBOUND = _crossinterp.UnboundItem.singleton('queue', __name__)
-
-
 def _serialize_unbound(unbound):
  if unbound is UNBOUND:
  unbound = _crossinterp.UNBOUND

Lib/test/test_concurrent_futures/test_interpreter_pool.py

@@ -427,6 +427,10 @@ def run(taskid, ready, blocker):
  ready.get(timeout=1) # blocking
  except interpreters.QueueEmpty:
  pass
+ except queues.QueueEmpty:
+ # GH-142414: reloading the _queues module makes get to raise
+ # queues.QueueEmpty instead of interpreters.QueueEmpty.
+ pass
  else:
  done += 1
  pending -= done

Lib/test/test_interpreters/test_queues.py

@@ -8,6 +8,7 @@
 # Raise SkipTest if subinterpreters not supported.
 _queues = import_helper.import_module('_interpqueues')
 from concurrent import interpreters
+from concurrent.futures import InterpreterPoolExecutor
 from concurrent.interpreters import _queues as queues, _crossinterp
 from .utils import _run_output, TestBase as _TestBase
 
@@ -93,6 +94,14 @@ def test_bind_release(self):
  with self.assertRaises(queues.QueueError):
  _queues.release(qid)
 
+ def test_interpreter_pool_executor_after_reload(self):
+ # Regression test for gh-142414 (KeyError in serialize_unbound).
+ importlib.reload(queues)
+ code = "import struct"
+ with InterpreterPoolExecutor(max_workers=1) as executor:
+ results = executor.map(exec, [code] * 1)
+ self.assertEqual(list(results), [None] * 1)
+
 
 class QueueTests(TestBase):
 

Misc/NEWS.d/next/Library/2025-12-10-15-27-58.gh-issue-142414.zTHgP-.rst

@@ -0,0 +1 @@
+Fix spurious :exc:`KeyError` when :mod:`!concurrent.interpreters._queues` is reloaded after import.