GH-79033: Fix asyncio.Server.wait_closed()

[gvanrossum]

wait_closed() was a no-op when used as recommended (after close()).

I had to debug one test (test__sock_sendfile_native_failure) -- the cleanup sequence for the test fixture was botched.

Hopefully that's not a portend of problems in user code -- this has never worked so people may well be doing this wrong. :-(

• Issue: Counter-intuitive behavior of Server.close() / wait_closed() #79033

[gvanrossum]

Needs test and news entry

[gvanrossum]

@kumaraditya303 Can you suggest a test for this?

[kumaraditya303]

Something like should work:

diff --git a/Lib/test/test_asyncio/test_server.py b/Lib/test/test_asyncio/test_server.py
index 860d62d52e..ceea4059ae 100644
--- a/Lib/test/test_asyncio/test_server.py
+++ b/Lib/test/test_asyncio/test_server.py
@@ -120,6 +120,26 @@ async def main(srv):
                 self.loop.run_until_complete(srv.serve_forever())
 
 
+class TestServer2(unittest.IsolatedAsyncioTestCase):
+
+    async def test_wait_closed(self):
+        async def serve(*args):
+            pass
+
+        srv = await asyncio.start_server(serve, socket_helper.HOSTv4, 0)
+
+        # active count = 0
+        wait = asyncio.create_task(srv.wait_closed())
+        await asyncio.sleep(0)
+        self.assertTrue(wait.done())
+
+        # active count != 0
+        srv._attach()
+        wait = asyncio.create_task(srv.wait_closed())
+        await asyncio.sleep(0)
+        self.assertFalse(wait.done())
+
+
 @unittest.skipUnless(hasattr(asyncio, 'ProactorEventLoop'), 'Windows only')
 class ProactorStartServerTests(BaseStartServer, unittest.TestCase):
 

Creating a test with an actual client seems rather flaky as it requires a heavy load on server so will be unreliable.

[gvanrossum]

Thanks! _attach exists for the transport to indicate that it's active. We should probably also call _detach (after closing the server) and then check that the wait_closed task finishes.

[kumaraditya303]

LGTM, thanks!

[gvanrossum]

Let’s not backport, I fear it will surprise some users since it never worked.