fix: guard against proactor accept-loop race on Windows (Python 3.14+)#2
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PolyphonyRequiem merged 1 commit intoinstall-combinedfrom Apr 24, 2026
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On Windows with Python 3.14+, the proactor event loop's accept callback can fire after Server.close() sets _sockets = None during shutdown, causing an AssertionError in base_events.py:_attach that crashes the workflow process. Fix: - Add _guarded_serve() wrapper that catches AssertionError when the uvicorn server is in shutdown state (should_exit = True) - Install a custom event-loop exception handler during server lifetime that suppresses the same race when it surfaces through callbacks - _is_proactor_shutdown_race() validates: AssertionError type, server shutdown state, and asyncio-originating traceback frames - Restore original exception handler in stop() The guard is narrowly scoped: only AssertionError during server shutdown is suppressed. All other exceptions delegate to the original handler. Tests: 9 new tests covering the race detection, exception handler delegation, guarded serve behavior, and edge cases. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Bug
Web dashboard crashes with
AssertionErrorin Python 3.14 asyncio proactor event loop on Windows when the server accepts a new connection during shutdown.Root cause: The proactor accept callback fires after
Server.close()sets_sockets = None— a race between the shutdown path and the accept loop.Fix
Two-layer guard, both narrowly scoped to only suppress
AssertionErrorwhen the uvicorn server is in shutdown state (should_exit = True):_guarded_serve()— wrapsserver.serve()to catch the error if it propagates through the coroutine chain_is_proactor_shutdown_race()validates: AssertionError type, server shutdown state, and asyncio-originating traceback frames. The original exception handler is saved and restored instop().Why not a separate thread?
Considered running uvicorn in a dedicated thread with a selector event loop, but cross-thread communication would break existing engine contracts (asyncio.Event/Queue used by workflow engine). Much higher complexity for the same outcome.
Tests
9 new tests covering race detection, exception handler delegation, guarded serve behavior, and edge cases. All 58 server tests pass.