first commit

.venv/Lib/site-packages/greenlet/tests/fail_switch_critical_section.py

@@ -0,0 +1,38 @@
+"""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)