Editing: fail_switch_critical_section.py

"""Out-of-process payload for the free-threaded switch/critical-section deadlock. See ``freethread_switch_deadlock.py`` in the repo root for the full write-up. Before the fix, a greenlet switch swapped C stacks but left any held ``PyCriticalSection`` locks (tracked in ``tstate->critical_section``) locked. asyncio's ``Task.__step`` holds such a lock on the running task across the step, so switching into a child greenlet and touching that task from there blocked forever. A fixed build (and any GIL-enabled build) prints the sentinel; a regressed free-threaded build deadlocks, and the watchdog turns that hang into a non-zero exit so the test fails loudly instead of stalling the whole suite. """ import asyncio import faulthandler import sys import greenlet # The deadlock is immediate when present; the generous timeout is only so a # genuinely regressed build still exits on the slowest CI, never on a good one. faulthandler.dump_traceback_later(15, exit=True) async def main(): task = asyncio.current_task() # its running __step holds a lock on `task` def in_child_fiber(): # Fresh C stack; the task's lock is still held by the fiber we left. # A regressed build never returns from this first call. task.add_done_callback(lambda _: None) task.remove_done_callback(lambda _: None) greenlet.greenlet(in_child_fiber).switch() asyncio.run(main()) faulthandler.cancel_dump_traceback_later() print("SWITCH CS OK") sys.exit(0)

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