From e5bd5ad70d9e549eeb80aadb4f3ccb0f2f23266d Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Fri, 13 Jan 2023 14:40:29 +0200 Subject: gh-100160: Restore and deprecate implicit creation of an event loop (GH-100410) Partially revert changes made in GH-93453. asyncio.DefaultEventLoopPolicy.get_event_loop() now emits a DeprecationWarning and creates and sets a new event loop instead of raising a RuntimeError if there is no current event loop set. Co-authored-by: Guido van Rossum --- Doc/library/asyncio-eventloop.rst | 10 +++---- Doc/library/asyncio-policy.rst | 8 +++-- Doc/whatsnew/3.10.rst | 13 -------- Doc/whatsnew/3.12.rst | 17 ++++------- Lib/asyncio/events.py | 24 ++++++++++++++- Lib/test/test_asyncio/test_events.py | 35 +++++++++++++++++++--- Lib/test/test_asyncio/test_unix_events.py | 8 +++-- .../2022-12-21-17-49-50.gh-issue-100160.N0NHRj.rst | 3 ++ 8 files changed, 77 insertions(+), 41 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2022-12-21-17-49-50.gh-issue-100160.N0NHRj.rst diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst index 470d1aa..db63a5d 100644 --- a/Doc/library/asyncio-eventloop.rst +++ b/Doc/library/asyncio-eventloop.rst @@ -48,7 +48,7 @@ an event loop: running event loop. If there is no running event loop set, the function will return - the result of calling ``get_event_loop_policy().get_event_loop()``. + the result of the ``get_event_loop_policy().get_event_loop()`` call. Because this function has rather complex behavior (especially when custom event loop policies are in use), using the @@ -59,11 +59,9 @@ an event loop: instead of using these lower level functions to manually create and close an event loop. - .. note:: - In Python versions 3.10.0--3.10.8 and 3.11.0 this function - (and other functions which used it implicitly) emitted a - :exc:`DeprecationWarning` if there was no running event loop, even if - the current loop was set. + .. deprecated:: 3.12 + Deprecation warning is emitted if there is no current event loop. + In some future Python release this will become an error. .. function:: set_event_loop(loop) diff --git a/Doc/library/asyncio-policy.rst b/Doc/library/asyncio-policy.rst index ccd9524..0d7821e 100644 --- a/Doc/library/asyncio-policy.rst +++ b/Doc/library/asyncio-policy.rst @@ -116,9 +116,11 @@ asyncio ships with the following built-in policies: On Windows, :class:`ProactorEventLoop` is now used by default. - .. versionchanged:: 3.12 - :meth:`get_event_loop` now raises a :exc:`RuntimeError` if there is no - current event loop set. + .. deprecated:: 3.12 + The :meth:`get_event_loop` method of the default asyncio policy now emits + a :exc:`DeprecationWarning` if there is no current event loop set and it + decides to create one. + In some future Python release this will become an error. .. class:: WindowsSelectorEventLoopPolicy diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst index 8296fb0..f6a48ed 100644 --- a/Doc/whatsnew/3.10.rst +++ b/Doc/whatsnew/3.10.rst @@ -1709,19 +1709,6 @@ Deprecated scheduled for removal in Python 3.12. (Contributed by Erlend E. Aasland in :issue:`42264`.) -* :func:`asyncio.get_event_loop` now emits a deprecation warning if there is - no running event loop. In the future it will be an alias of - :func:`~asyncio.get_running_loop`. - :mod:`asyncio` functions which implicitly create :class:`~asyncio.Future` - or :class:`~asyncio.Task` objects now emit - a deprecation warning if there is no running event loop and no explicit - *loop* argument is passed: :func:`~asyncio.ensure_future`, - :func:`~asyncio.wrap_future`, :func:`~asyncio.gather`, - :func:`~asyncio.shield`, :func:`~asyncio.as_completed` and constructors of - :class:`~asyncio.Future`, :class:`~asyncio.Task`, - :class:`~asyncio.StreamReader`, :class:`~asyncio.StreamReaderProtocol`. - (Contributed by Serhiy Storchaka in :issue:`39529`.) - * The undocumented built-in function ``sqlite3.enable_shared_cache`` is now deprecated, scheduled for removal in Python 3.12. Its use is strongly discouraged by the SQLite3 documentation. See `the SQLite3 docs diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst index 7d318ca..2c807ca 100644 --- a/Doc/whatsnew/3.12.rst +++ b/Doc/whatsnew/3.12.rst @@ -408,6 +408,11 @@ Deprecated :exc:`ImportWarning`). (Contributed by Brett Cannon in :gh:`65961`.) +* The :meth:`~asyncio.DefaultEventLoopPolicy.get_event_loop` method of the + default event loop policy now emits a :exc:`DeprecationWarning` if there + is no current event loop set and it decides to create one. + (Contributed by Serhiy Storchaka and Guido van Rossum in :gh:`100160`.) + Pending Removal in Python 3.13 ------------------------------ @@ -710,18 +715,6 @@ Changes in the Python API around process-global resources, which are best managed from the main interpreter. (Contributed by Dong-hee Na in :gh:`99127`.) -* :func:`asyncio.get_event_loop` and many other :mod:`asyncio` functions like - :func:`~asyncio.ensure_future`, :func:`~asyncio.shield` or - :func:`~asyncio.gather`, and also the - :meth:`~asyncio.BaseDefaultEventLoopPolicy.get_event_loop` method of - :class:`~asyncio.BaseDefaultEventLoopPolicy` now raise a :exc:`RuntimeError` - if called when there is no running event loop and the current event loop was - not set. - Previously they implicitly created and set a new current event loop. - :exc:`DeprecationWarning` is no longer emitted if there is no running - event loop but the current event loop is set in the policy. - (Contributed by Serhiy Storchaka in :gh:`93453`.) - Build Changes ============= diff --git a/Lib/asyncio/events.py b/Lib/asyncio/events.py index 6cff8c5..ce44942 100644 --- a/Lib/asyncio/events.py +++ b/Lib/asyncio/events.py @@ -619,7 +619,7 @@ class AbstractEventLoopPolicy: Returns an event loop object implementing the BaseEventLoop interface, or raises an exception in case no event loop has been set for the - current context. + current context and the current policy does not specify to create one. It should never return None.""" raise NotImplementedError @@ -672,6 +672,28 @@ class BaseDefaultEventLoopPolicy(AbstractEventLoopPolicy): Returns an instance of EventLoop or raises an exception. """ + if (self._local._loop is None and + not self._local._set_called and + threading.current_thread() is threading.main_thread()): + stacklevel = 2 + try: + f = sys._getframe(1) + except AttributeError: + pass + else: + # Move up the call stack so that the warning is attached + # to the line outside asyncio itself. + while f: + module = f.f_globals.get('__name__') + if not (module == 'asyncio' or module.startswith('asyncio.')): + break + f = f.f_back + stacklevel += 1 + import warnings + warnings.warn('There is no current event loop', + DeprecationWarning, stacklevel=stacklevel) + self.set_event_loop(self.new_event_loop()) + if self._local._loop is None: raise RuntimeError('There is no current event loop in thread %r.' % threading.current_thread().name) diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py index 093f8c1..214544b 100644 --- a/Lib/test/test_asyncio/test_events.py +++ b/Lib/test/test_asyncio/test_events.py @@ -2614,8 +2614,33 @@ class PolicyTests(unittest.TestCase): def test_get_event_loop(self): policy = asyncio.DefaultEventLoopPolicy() self.assertIsNone(policy._local._loop) - with self.assertRaisesRegex(RuntimeError, 'no current event loop'): - policy.get_event_loop() + with self.assertWarns(DeprecationWarning) as cm: + loop = policy.get_event_loop() + self.assertEqual(cm.filename, __file__) + self.assertIsInstance(loop, asyncio.AbstractEventLoop) + + self.assertIs(policy._local._loop, loop) + self.assertIs(loop, policy.get_event_loop()) + loop.close() + + def test_get_event_loop_calls_set_event_loop(self): + policy = asyncio.DefaultEventLoopPolicy() + + with mock.patch.object( + policy, "set_event_loop", + wraps=policy.set_event_loop) as m_set_event_loop: + + with self.assertWarns(DeprecationWarning) as cm: + loop = policy.get_event_loop() + self.addCleanup(loop.close) + self.assertEqual(cm.filename, __file__) + + # policy._local._loop must be set through .set_event_loop() + # (the unix DefaultEventLoopPolicy needs this call to attach + # the child watcher correctly) + m_set_event_loop.assert_called_with(loop) + + loop.close() def test_get_event_loop_after_set_none(self): policy = asyncio.DefaultEventLoopPolicy() @@ -2801,8 +2826,10 @@ class GetEventLoopTestsMixin: loop = asyncio.new_event_loop() self.addCleanup(loop.close) - with self.assertRaisesRegex(RuntimeError, 'no current'): - asyncio.get_event_loop() + with self.assertWarns(DeprecationWarning) as cm: + loop2 = asyncio.get_event_loop() + self.addCleanup(loop2.close) + self.assertEqual(cm.filename, __file__) asyncio.set_event_loop(None) with self.assertRaisesRegex(RuntimeError, 'no current'): asyncio.get_event_loop() diff --git a/Lib/test/test_asyncio/test_unix_events.py b/Lib/test/test_asyncio/test_unix_events.py index 600a590..33d0ea1 100644 --- a/Lib/test/test_asyncio/test_unix_events.py +++ b/Lib/test/test_asyncio/test_unix_events.py @@ -1884,7 +1884,9 @@ class TestFork(unittest.IsolatedAsyncioTestCase): if pid == 0: # child try: - loop = asyncio.get_event_loop_policy().get_event_loop() + with self.assertWarns(DeprecationWarning): + loop = asyncio.get_event_loop_policy().get_event_loop() + os.write(w, b'LOOP:' + str(id(loop)).encode()) except RuntimeError: os.write(w, b'NO LOOP') except: @@ -1893,7 +1895,9 @@ class TestFork(unittest.IsolatedAsyncioTestCase): os._exit(0) else: # parent - self.assertEqual(os.read(r, 100), b'NO LOOP') + result = os.read(r, 100) + self.assertEqual(result[:5], b'LOOP:', result) + self.assertNotEqual(int(result[5:]), id(loop)) wait_process(pid, exitcode=0) @hashlib_helper.requires_hashdigest('md5') diff --git a/Misc/NEWS.d/next/Library/2022-12-21-17-49-50.gh-issue-100160.N0NHRj.rst b/Misc/NEWS.d/next/Library/2022-12-21-17-49-50.gh-issue-100160.N0NHRj.rst new file mode 100644 index 0000000..d5cc785 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2022-12-21-17-49-50.gh-issue-100160.N0NHRj.rst @@ -0,0 +1,3 @@ +Emit a deprecation warning in +:meth:`asyncio.DefaultEventLoopPolicy.get_event_loop` if there is no current +event loop set and it decides to create one. -- cgit v0.12