gh-121723: Relax constraints on queue objects for `logging.handlers.QueueHandler`. (GH-122154)

1 files changed, 29 insertions, 26 deletions

diff --git a/Lib/logging/config.py b/Lib/logging/config.py
index 95e129a..3781cb1 100644
--- a/Lib/logging/config.py
+++ b/Lib/logging/config.py
@@ -497,6 +497,33 @@ class BaseConfigurator(object):
             value = tuple(value)
         return value
 
+def _is_queue_like_object(obj):
+    """Check that *obj* implements the Queue API."""
+    if isinstance(obj, queue.Queue):
+        return True
+    # defer importing multiprocessing as much as possible
+    from multiprocessing.queues import Queue as MPQueue
+    if isinstance(obj, MPQueue):
+        return True
+    # Depending on the multiprocessing start context, we cannot create
+    # a multiprocessing.managers.BaseManager instance 'mm' to get the
+    # runtime type of mm.Queue() or mm.JoinableQueue() (see gh-119819).
+    #
+    # Since we only need an object implementing the Queue API, we only
+    # do a protocol check, but we do not use typing.runtime_checkable()
+    # and typing.Protocol to reduce import time (see gh-121723).
+    #
+    # Ideally, we would have wanted to simply use strict type checking
+    # instead of a protocol-based type checking since the latter does
+    # not check the method signatures.
+    queue_interface = [
+        'empty', 'full', 'get', 'get_nowait',
+        'put', 'put_nowait', 'join', 'qsize',
+        'task_done',
+    ]
+    return all(callable(getattr(obj, method, None))
+               for method in queue_interface)
+
 class DictConfigurator(BaseConfigurator):
     """
     Configure logging using a dictionary-like object to describe the
@@ -791,32 +818,8 @@ class DictConfigurator(BaseConfigurator):
                         if '()' not in qspec:
                             raise TypeError('Invalid queue specifier %r' % qspec)
                         config['queue'] = self.configure_custom(dict(qspec))
-                    else:
-                        from multiprocessing.queues import Queue as MPQueue
-
-                        if not isinstance(qspec, (queue.Queue, MPQueue)):
-                            # Safely check if 'qspec' is an instance of Manager.Queue
-                            # / Manager.JoinableQueue
-
-                            from multiprocessing import Manager as MM
-                            from multiprocessing.managers import BaseProxy
-
-                            # if it's not an instance of BaseProxy, it also can't be
-                            # an instance of Manager.Queue / Manager.JoinableQueue
-                            if isinstance(qspec, BaseProxy):
-                                # Sometimes manager or queue creation might fail
-                                # (e.g. see issue gh-120868). In that case, any
-                                # exception during the creation of these queues will
-                                # propagate up to the caller and be wrapped in a
-                                # `ValueError`, whose cause will indicate the details of
-                                # the failure.
-                                mm = MM()
-                                proxy_queue = mm.Queue()
-                                proxy_joinable_queue = mm.JoinableQueue()
-                                if not isinstance(qspec, (type(proxy_queue), type(proxy_joinable_queue))):
-                                    raise TypeError('Invalid queue specifier %r' % qspec)
-                            else:
-                                raise TypeError('Invalid queue specifier %r' % qspec)
+                    elif not _is_queue_like_object(qspec):
+                        raise TypeError('Invalid queue specifier %r' % qspec)
 
                 if 'listener' in config:
                     lspec = config['listener']