Implement loop.shutdown_default_executor()

[aeros]

Closes #349.

Since I don't have too much experience with Cython, I wasn't entirely certain about the purpose of uvloop/includes/stdlib.pxi, but I assumed that threading.Thread should be included there since it was also done for concurrent.futures.ThreadPoolExecutor. At a glance, it seems to be a means of importing the classes from stdlib modules at compile time rather than at run time? I'd appreciate clarification on this if anyone has the time to explain.

Otherwise, it's mostly similar to the reference implementation in asyncio.

[aeros]

/cc @1st1

[aeros]

The MacOS CI failures seem to be build-related and not due to the PR. I'm seeing similar CI failures in the most recent commit.

[aeros]

I'll wait on squashing into a single commit until the review process is complete, since it tends to affect previous review comments after force-pushing to the PR branch.

[1st1]

Is this the only test we have in cpython/asyncio/tests?

[aeros]

Actually, it looks like this is the only test that uses it in CPython:

    def test_run_in_executor_cancel(self):
        called = False

        def patched_call_soon(*args):
            nonlocal called
            called = True

        def run():
            time.sleep(0.05)

        f2 = self.loop.run_in_executor(None, run)
        f2.cancel()
        self.loop.run_until_complete(
                self.loop.shutdown_default_executor())
        self.loop.close()
        self.loop.call_soon = patched_call_soon
        self.loop.call_soon_threadsafe = patched_call_soon
        time.sleep(0.4)
        self.assertFalse(called)

In retrospect, I probably should have added some dedicated test(s) for shutdown_default_executor() in the PR that added it in the first place, but at the time, I didn't have a decent understanding of asyncio unit tests. Should I add this one to the CPython regression tests and maybe a couple more if I can think of some that could be useful?

Note: It's also used in test_threads.py for a tearDown() and utils.py for close_loop(). But those are hardly dedicated tests, so I didn't include it above.

[1st1]

Should I add this one to the CPython regression tests and maybe a couple more if I can think of some that could be useful?

The more tests the better :) If they are not redundant, of course. I'll merge this PR now, huge thanks!

[qeternity]

Over 4 months since this was merged - is there any hope for a new pypi release?

[1st1]

In the next couple of weeks.

[qeternity]

@1st1 not to be a nag but anything that the community can do in terms of preflight checks?