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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`test_multiprocessing_spawn.test_processes` flaky tests on Windows","articleBody":"# Bug report\n\nSeen on Windows free threading build, but not free threading specific:\n\nhttps://github.com/python/cpython/actions/runs/13606907022/job/38039459160?pr=130732\n\nThis is in Windows specific code. Not yet sure if this is free threading specific.\n\n```\nERROR: test_async_error_callback (test.test_multiprocessing_spawn.test_processes.WithProcessesTestPoolWorkerErrors.test_async_error_callback)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"D:\\a\\cpython\\cpython\\Lib\\test\\_test_multiprocessing.py\", line 3101, in test_async_error_callback\n    p.close()\n    ~~~~~~~^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\pool.py\", line 652, in close\n    self._change_notifier.put(None)\n    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\queues.py\", line 394, in put\n    self._writer.send_bytes(obj)\n    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\connection.py\", line 206, in send_bytes\n    self._send_bytes(m[offset:offset + size])\n    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\connection.py\", line 293, in _send_bytes\n    raise ValueError(\"concurrent send_bytes() calls \"\n                     \"are not supported\")\nValueError: concurrent send_bytes() calls are not supported\n```\n\n\u003cdetails\u003e\n\u003csummary\u003e Also `test_traceback`: \u003c/summary\u003e\n\n\n```\nERROR: test_traceback (test.test_multiprocessing_spawn.test_processes.WithProcessesTestPool.test_traceback)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n  File \"D:\\a\\cpython\\cpython\\Lib\\test\\_test_multiprocessing.py\", line 2974, in test_traceback\n    with self.Pool(1) as p:\n         ~~~~~~~~~^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\pool.py\", line 739, in __exit__\n    self.terminate()\n    ~~~~~~~~~~~~~~^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\pool.py\", line 657, in terminate\n    self._terminate()\n    ~~~~~~~~~~~~~~~^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\util.py\", line 216, in __call__\n    res = self._callback(*self._args, **self._kwargs)\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\pool.py\", line 690, in _terminate_pool\n    change_notifier.put(None)\n    ~~~~~~~~~~~~~~~~~~~^^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\queues.py\", line 394, in put\n    self._writer.send_bytes(obj)\n    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\connection.py\", line 206, in send_bytes\n    self._send_bytes(m[offset:offset + size])\n    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"D:\\a\\cpython\\cpython\\Lib\\multiprocessing\\connection.py\", line 293, in _send_bytes\n    raise ValueError(\"concurrent send_bytes() calls \"\n                     \"are not supported\")\nValueError: concurrent send_bytes() calls are not supported\n```\n\u003c/details\u003e","author":{"url":"https://github.com/colesbury","@type":"Person","name":"colesbury"},"datePublished":"2025-03-01T17:21:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/130733/cpython/issues/130733"}