As discussed, we want to make Server objects more usable in async/await code and more compatible with asyncio.run.This is also needed to handle a use case when two or more servers are created and need to start listening at the same time.We propose to:1. Add a new bool flag defaulting to True to loop.create_server and loop.create_unix_server: start_serving.  By default, loop will return a server that is already accepting connections.  When start_serving is set to False, create_server and create_unix_server will return a server that will not listen on its sockets.2. A new idempotent Server.start_serving() method can be used to make server listen on its sockets (useful when a server object was created with start_serving=False).3. A new Server.serve_forever() method that calls start_serving() and blocks forever, until cancelled.  When cancelled, it closes its server object.4. A new Server.is_serving() method.  This is useful to introspect a server object in unittests.5. Server objects should be async context managers.  Server.__aexit__ should close the server and await on Server.wait_closed().With these new APIs, the following pattern becomes possible:    async def main():        srv = await asyncio.start_server(...)        async with srv:            await srv.serve_forever()    asyncio.run(main())

New changesetc9070d03f5169ad6e171e641b7fa8feab18bf229 by Yury Selivanov in branch 'master':bpo-32662: Implement Server.start_serving() and Server.serve_forever() (#5312)https://github.com/python/cpython/commit/c9070d03f5169ad6e171e641b7fa8feab18bf229

New changeset4112c5b97d9c1c7b034653d0e017ffa894a45c74 by Yury Selivanov in branch 'master':bpo-32662: Try making test_asyncio.test_server more reliable (#5338)https://github.com/python/cpython/commit/4112c5b97d9c1c7b034653d0e017ffa894a45c74

test_asyncio.test_start_server_1() hangs on "s390x Debian 3.x" buildbot:http://buildbot.python.org/all/#builders/13/builds/579test_set_nodelay (test.test_asyncio.test_selector_events.TestSelectorUtils) ... oktest_start_server_1 (test.test_asyncio.test_server.ProactorStartServerTests) ... skipped 'Windows only'Exception in thread test-client:Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/functional.py", line 193, in run    self._prog(TestSocketWrapper(self._sock))  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/test_server.py", line 44, in <lambda>    with self.tcp_client(lambda sock: client(sock, addr)):  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/test_server.py", line 19, in client    sock.connect(addr)ConnectionRefusedError: [Errno 111] Connection refusedDuring handling of the above exception, another exception occurred:Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/threading.py", line 917, in _bootstrap_inner    self.run()  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/functional.py", line 195, in run    self._test._abort_socket_test(ex)  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/functional.py", line 122, in _abort_socket_test    self.fail(ex)  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/case.py", line 680, in fail    raise self.failureException(msg)AssertionError: [Errno 111] Connection refusedTimeout (0:15:00)!Thread 0x000003fffcdcd710 (most recent call first):  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/selectors.py", line 468 in select  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/asyncio/base_events.py", line 1555 in _run_once  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/asyncio/base_events.py", line 450 in run_forever  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/asyncio/base_events.py", line 482 in run_until_complete  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_asyncio/test_server.py", line 45 in test_start_server_1  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/case.py", line 615 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/case.py", line 663 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 122 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 84 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 122 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 84 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 122 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 84 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 122 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 84 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 122 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/suite.py", line 84 in __call__  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/unittest/runner.py", line 176 in run  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/support/__init__.py", line 1861 in _run_suite  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/support/__init__.py", line 1951 in run_unittest  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/runtest.py", line 175 in test_runner  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/runtest.py", line 176 in runtest_inner  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/runtest.py", line 140 in runtest  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/main.py", line 291 in rerun_failed_tests  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/main.py", line 540 in _main  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/main.py", line 510 in main  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/libregrtest/main.py", line 585 in main  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/__main__.py", line 2 in <module>  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/runpy.py", line 85 in _run_code  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/runpy.py", line 193 in _run_module_as_maintest_start_server_1 (test.test_asyncio.test_server.SelectorStartServerTests) ... Makefile:1090: recipe for target 'buildbottest' failedmake: *** [buildbottest] Error 1program finished with exit code 2elapsedTime=2050.270461

The test fails differently on s390x SLES 3.x:http://buildbot.python.org/all/#/builders/16/builds/576...test_force_close (test.test_asyncio.test_selector_events.SelectorTransportTests) ... oktest_set_nodelay (test.test_asyncio.test_selector_events.TestSelectorUtils) ... oktest_start_server_1 (test.test_asyncio.test_server.ProactorStartServerTests) ... skipped 'Windows only'test_start_server_1 (test.test_asyncio.test_server.SelectorStartServerTests) ... Exception in thread test-client:Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/functional.py", line 193, in run    self._prog(TestSocketWrapper(self._sock))  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_server.py", line 44, in <lambda>    with self.tcp_client(lambda sock: client(sock, addr)):  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_server.py", line 19, in client    sock.connect(addr)ConnectionRefusedError: [Errno 111] Connection refusedDuring handling of the above exception, another exception occurred:Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/threading.py", line 917, in _bootstrap_inner    self.run()  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/functional.py", line 195, in run    self._test._abort_socket_test(ex)  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/functional.py", line 122, in _abort_socket_test    self.fail(ex)  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/unittest/case.py", line 680, in fail    raise self.failureException(msg)AssertionError: [Errno 111] Connection refused/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_server.py:45: ResourceWarning: unclosed <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 56340)>  self.loop.run_until_complete(main_task)ERRORtest_start_unix_server_1 (test.test_asyncio.test_server.SelectorStartServerTests) ... oktest_start_tls_client_1 (test.test_asyncio.test_sslproto.ProactorStartTLSTests) ... skipped 'Windows only'test_start_tls_server_1 (test.test_asyncio.test_sslproto.ProactorStartTLSTests) ... skipped 'Windows only'test_start_tls_wrong_args (test.test_asyncio.test_sslproto.ProactorStartTLSTests) ... skipped 'Windows only'test_start_tls_client_1 (test.test_asyncio.test_sslproto.SelectorStartTLSTests) ... /home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/collections/__init__.py:404: ResourceWarning: unclosed <socket.socket fd=7, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('127.0.0.1', 42302)>  result = _self._make(map(kwds.pop, field_names, _self))Unhandled error in exception handlercontext: {'message': 'Task was destroyed but it is pending!', 'task': <Task pending coro=<BaseStartServer.test_start_server_1.<locals>.main() done, defined at /home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_server.py:31> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x3fff979bbf8>()]>>}Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/asyncio/base_events.py", line 1459, in call_exception_handler    self._exception_handler(self, context)  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/functional.py", line 22, in loop_exception_handler    self.loop.default_exception_handler(context)AttributeError: 'NoneType' object has no attribute 'default_exception_handler'oktest_start_tls_server_1 (test.test_asyncio.test_sslproto.SelectorStartTLSTests) ... oktest_start_tls_wrong_args (test.test_asyncio.test_sslproto.SelectorStartTLSTests) ... oktest_cancel_handshake (test.test_asyncio.test_sslproto.SslProtoHandshakeTests) ... oktest_close_during_handshake (test.test_asyncio.test_sslproto.SslProtoHandshakeTests) ....======================================================================ERROR: test_start_server_1 (test.test_asyncio.test_server.SelectorStartServerTests)----------------------------------------------------------------------Traceback (most recent call last):  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/test/test_asyncio/test_server.py", line 45, in test_start_server_1    self.loop.run_until_complete(main_task)  File "/home/dje/cpython-buildarea/3.x.edelsohn-sles-z/build/Lib/asyncio/base_events.py", line 493, in run_until_complete    raise RuntimeError('Event loop stopped before Future completed.')RuntimeError: Event loop stopped before Future completed.----------------------------------------------------------------------

Just to be complete, the test also fails on x86 Gentoo Non-Debug with X 3.x:http://buildbot.python.org/all/#/builders/99/builds/564...test_start_server_1 (test.test_asyncio.test_server.SelectorStartServerTests) ... Exception in thread test-client:Traceback (most recent call last):  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/functional.py", line 193, in run    self._prog(TestSocketWrapper(self._sock))  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/test_server.py", line 44, in <lambda>    with self.tcp_client(lambda sock: client(sock, addr)):  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/test_server.py", line 19, in client    sock.connect(addr)ConnectionRefusedError: [Errno 111] Connection refusedDuring handling of the above exception, another exception occurred:Traceback (most recent call last):  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/threading.py", line 917, in _bootstrap_inner    self.run()  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/functional.py", line 195, in run    self._test._abort_socket_test(ex)  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/functional.py", line 122, in _abort_socket_test    self.fail(ex)  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/unittest/case.py", line 680, in fail    raise self.failureException(msg)AssertionError: [Errno 111] Connection refusedTimeout (0:15:00)!Thread 0xb7d69700 (most recent call first):  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/selectors.py", line 468 in select  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/asyncio/base_events.py", line 1555 in _run_once  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/asyncio/base_events.py", line 450 in run_forever  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/asyncio/base_events.py", line 482 in run_until_complete  File "/buildbot/buildarea/3.x.ware-gentoo-x86.nondebug/build/Lib/test/test_asyncio/test_server.py", line 45 in test_start_server_1...

I think these failures were on the previous version of the test; i've fixed it last night and it shouldn't timeout this way anymore.