Intermittent failure in ` test_sys.SysModuleTest.test_current_exceptions`

[FFY00]

Bug report

Bug description:

Example: https://github.com/python/cpython/actions/runs/6502915514/job/17662666558?pr=110794

The code in question:

cpython/Lib/test/test_sys.py

Lines 507 to 572 in b883cad

	def test_current_exceptions(self):
	import threading
	import traceback
	# Spawn a thread that blocks at a known place. Then the main
	# thread does sys._current_frames(), and verifies that the frames
	# returned make sense.
	entered_g = threading.Event()
	leave_g = threading.Event()
	thread_info = [] # the thread's id
	def f123():
	g456()
	def g456():
	thread_info.append(threading.get_ident())
	entered_g.set()
	while True:
	try:
	raise ValueError("oops")
	except ValueError:
	if leave_g.wait(timeout=support.LONG_TIMEOUT):
	break
	t = threading.Thread(target=f123)
	t.start()
	entered_g.wait()
	try:
	# At this point, t has finished its entered_g.set(), although it's
	# impossible to guess whether it's still on that line or has moved on
	# to its leave_g.wait().
	self.assertEqual(len(thread_info), 1)
	thread_id = thread_info[0]
	d = sys._current_exceptions()
	for tid in d:
	self.assertIsInstance(tid, int)
	self.assertGreater(tid, 0)
	main_id = threading.get_ident()
	self.assertIn(main_id, d)
	self.assertIn(thread_id, d)
	self.assertEqual(None, d.pop(main_id))
	# Verify that the captured thread frame is blocked in g456, called
	# from f123. This is a little tricky, since various bits of
	# threading.py are also in the thread's call stack.
	exc_value = d.pop(thread_id)
	stack = traceback.extract_stack(exc_value.__traceback__.tb_frame)
	for i, (filename, lineno, funcname, sourceline) in enumerate(stack):
	if funcname == "f123":
	break
	else:
	self.fail("didn't find f123() on thread's call stack")
	self.assertEqual(sourceline, "g456()")
	# And the next record must be for g456().
	filename, lineno, funcname, sourceline = stack[i+1]
	self.assertEqual(funcname, "g456")
	self.assertTrue(sourceline.startswith("if leave_g.wait("))
	finally:
	# Reap the spawned thread.
	leave_g.set()
	t.join()

Originally added in 64366fa

I believe the failure is due to sys._current_exceptions being run before the exception is raised.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• GH-110796: fix intermittent test failure in test_current_exceptions #110797

[hugovk]

Thanks for the fix!