fix: Don't assume ordering of ThreadPoolExecutor submissions

[holmanb]

Proposed Commit Message

fix: Don't assume ordering of ThreadPoolExecutor submissions

This test breaks in Python 3.13 and was never guaranteed to
succeed in earlier versions of Python but apparently did due
to the way that cPython was implementated previously.

Additional Context

We've had some flaky test failures for a bit now: [example]

This test was never guaranteed to succeed, it just apparently did because of cPython ThreadpoolExecutor implementation. Python 3.13 brings lots of threading changes - it is unsurprising that this test now fails occasionally.

self = <tests.unittests.test_url_helper.TestDualStack object at 0x7f07de5e12e0>

    def test_dual_stack_staggered(self):
        """Assert expected call intervals occur"""
        stagger = 0.1
        with mock.patch(M_PATH + "_run_func_with_delay") as delay_func:
            dual_stack(
                lambda x, _y: x,
                ["you", "and", "me", "and", "dog"],
                stagger_delay=stagger,
                timeout=1,
            )
    
            # ensure that stagger delay for each subsequent call is:
            # [ 0 * N, 1 * N, 2 * N, 3 * N, 4 * N, 5 * N] where N = stagger
            # it appears that without an explicit wait/join we can't assert
            # number of calls
            for delay, call_item in enumerate(delay_func.call_args_list):
                _, kwargs = call_item
>               assert stagger * delay == kwargs.get("delay")
E               AssertionError: assert (0.1 * 1) == 0.2
E                +  where 0.2 = <built-in method get of dict object at 0x7f077cee4d40>('delay')
E                +    where <built-in method get of dict object at 0x7f077cee4d40> = {'addr': 'me', 'delay': 0.2, 'event': <threading.Event at 0x7f07ac855700: set>, 'func': <function TestDualStack.test_dual_stack_staggered.<locals>.<lambda> at 0x7f077cef02c0>, ...}.get

_          = ()
call_item  = call(func=<function TestDualStack.test_dual_stack_staggered.<locals>.<lambda> at 0x7f077cef02c0>, addr='me', timeout=1, event=<threading.Event at 0x7f07ac855700: set>, delay=0.2)
delay      = 1
delay_func = <MagicMock name='_run_func_with_delay' id='139670934497200'>
kwargs     = {'addr': 'me',
 'delay': 0.2,
 'event': <threading.Event at 0x7f07ac855700: set>,
 'func': <function TestDualStack.test_dual_stack_staggered.<locals>.<lambda> at 0x7f077cef02c0>,
 'timeout': 1}
self       = <tests.unittests.test_url_helper.TestDualStack object at 0x7f07de5e12e0>
stagger    = 0.1

Test Steps

It passes for me locally and I don't have a Python 3.13 interpreter locally so... did ci pass?

[TheRealFalcon]

LGTM! If I run this test in a loop on main I get a failure within 10 tries. I have been running this branch in a loop while reviewing the changes and we're up to 200 runs without failure.

It passes for me locally and I don't have a Python 3.13 interpreter locally so... did ci pass?

pyenv is your friend 🙂