gh-97696: asyncio eager tasks factory (#102853)

Co-authored-by: Jacob Bower <jbower@meta.com>
Co-authored-by: Carol Willing <carolcode@willingconsulting.com>

Doc/library/asyncio-task.rst

@@ -527,6 +527,42 @@ Running Tasks Concurrently
       and there is no running event loop.
 
 
+Eager Task Factory
+==================
+
+.. function:: eager_task_factory(loop, coro, *, name=None, context=None)
+
+    A task factory for eager task execution.
+
+    When using this factory (via :meth:`loop.set_task_factory(asyncio.eager_task_factory) <loop.set_task_factory>`),
+    coroutines begin execution synchronously during :class:`Task` construction.
+    Tasks are only scheduled on the event loop if they block.
+    This can be a performance improvement as the overhead of loop scheduling
+    is avoided for coroutines that complete synchronously.
+
+    A common example where this is beneficial is coroutines which employ
+    caching or memoization to avoid actual I/O when possible.
+
+    .. note::
+
+        Immediate execution of the coroutine is a semantic change.
+        If the coroutine returns or raises, the task is never scheduled
+        to the event loop. If the coroutine execution blocks, the task is
+        scheduled to the event loop. This change may introduce behavior
+        changes to existing applications. For example,
+        the application's task execution order is likely to change.
+
+    .. versionadded:: 3.12
+
+.. function:: create_eager_task_factory(custom_task_constructor)
+
+    Create an eager task factory, similar to :func:`eager_task_factory`,
+    using the provided *custom_task_constructor* when creating a new task instead
+    of the default :class:`Task`.
+
+    .. versionadded:: 3.12
+
+
 Shielding From Cancellation
 ===========================
 

Doc/whatsnew/3.12.rst

@@ -613,6 +613,11 @@ Optimizations
 * Speed up :class:`asyncio.Task` creation by deferring expensive string formatting.
   (Contributed by Itamar O in :gh:`103793`.)
 
+* Added :func:`asyncio.eager_task_factory` and :func:`asyncio.create_eager_task_factory`
+  functions to allow opting an event loop in to eager task execution,
+  speeding up some use-cases by up to 50%.
+  (Contributed by Jacob Bower & Itamar O in :gh:`102853`)
+
 
 CPython bytecode changes
 ========================

Include/internal/pycore_global_objects_fini_generated.h

@@ -882,6 +882,7 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) {
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(dst_dir_fd));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(duration));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(e));
+    _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(eager_start));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(effective_ids));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(element_factory));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(encode));
@@ -972,6 +973,7 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) {
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(instructions));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(intern));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(intersection));
+    _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(is_running));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(isatty));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(isinstance));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(isoformat));

Include/internal/pycore_global_strings.h

@@ -370,6 +370,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(dst_dir_fd)
         STRUCT_FOR_ID(duration)
         STRUCT_FOR_ID(e)
+        STRUCT_FOR_ID(eager_start)
         STRUCT_FOR_ID(effective_ids)
         STRUCT_FOR_ID(element_factory)
         STRUCT_FOR_ID(encode)
@@ -460,6 +461,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(instructions)
         STRUCT_FOR_ID(intern)
         STRUCT_FOR_ID(intersection)
+        STRUCT_FOR_ID(is_running)
         STRUCT_FOR_ID(isatty)
         STRUCT_FOR_ID(isinstance)
         STRUCT_FOR_ID(isoformat)

Include/internal/pycore_runtime_init_generated.h

@@ -876,6 +876,7 @@ extern "C" {
     INIT_ID(dst_dir_fd), \
     INIT_ID(duration), \
     INIT_ID(e), \
+    INIT_ID(eager_start), \
     INIT_ID(effective_ids), \
     INIT_ID(element_factory), \
     INIT_ID(encode), \
@@ -966,6 +967,7 @@ extern "C" {
     INIT_ID(instructions), \
     INIT_ID(intern), \
     INIT_ID(intersection), \
+    INIT_ID(is_running), \
     INIT_ID(isatty), \
     INIT_ID(isinstance), \
     INIT_ID(isoformat), \

Include/internal/pycore_unicodeobject_generated.h

@@ -963,6 +963,9 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) {
     string = &_Py_ID(e);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);
+    string = &_Py_ID(eager_start);
+    assert(_PyUnicode_CheckConsistency(string, 1));
+    _PyUnicode_InternInPlace(interp, &string);
     string = &_Py_ID(effective_ids);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);
@@ -1233,6 +1236,9 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) {
     string = &_Py_ID(intersection);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);
+    string = &_Py_ID(is_running);
+    assert(_PyUnicode_CheckConsistency(string, 1));
+    _PyUnicode_InternInPlace(interp, &string);
     string = &_Py_ID(isatty);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);

Lib/asyncio/base_tasks.py

@@ -15,11 +15,13 @@ def _task_repr_info(task):
 
     info.insert(1, 'name=%r' % task.get_name())
 
+    if task._fut_waiter is not None:
+        info.insert(2, f'wait_for={task._fut_waiter!r}')
+
+    if task._coro:
         coro = coroutines._format_coroutine(task._coro)
         info.insert(2, f'coro=<{coro}>')
 
-    if task._fut_waiter is not None:
-        info.insert(3, f'wait_for={task._fut_waiter!r}')
     return info
 
 

Lib/asyncio/tasks.py

@@ -6,6 +6,7 @@ __all__ = (
     'wait', 'wait_for', 'as_completed', 'sleep',
     'gather', 'shield', 'ensure_future', 'run_coroutine_threadsafe',
     'current_task', 'all_tasks',
+    'create_eager_task_factory', 'eager_task_factory',
     '_register_task', '_unregister_task', '_enter_task', '_leave_task',
 )
 
@@ -43,22 +44,26 @@ def all_tasks(loop=None):
     """Return a set of all tasks for the loop."""
     if loop is None:
         loop = events.get_running_loop()
-    # Looping over a WeakSet (_all_tasks) isn't safe as it can be updated from another
+    # capturing the set of eager tasks first, so if an eager task "graduates"
-    # thread while we do so. Therefore we cast it to list prior to filtering. The list
+    # to a regular task in another thread, we don't risk missing it.
-    # cast itself requires iteration, so we repeat it several times ignoring
+    eager_tasks = list(_eager_tasks)
-    # RuntimeErrors (which are not very likely to occur). See issues 34970 and 36607 for
+    # Looping over the WeakSet isn't safe as it can be updated from another
-    # details.
+    # thread, therefore we cast it to list prior to filtering. The list cast
+    # itself requires iteration, so we repeat it several times ignoring
+    # RuntimeErrors (which are not very likely to occur).
+    # See issues 34970 and 36607 for details.
+    scheduled_tasks = None
     i = 0
     while True:
         try:
-            tasks = list(_all_tasks)
+            scheduled_tasks = list(_scheduled_tasks)
         except RuntimeError:
             i += 1
             if i >= 1000:
                 raise
         else:
             break
-    return {t for t in tasks
+    return {t for t in itertools.chain(scheduled_tasks, eager_tasks)
             if futures._get_loop(t) is loop and not t.done()}
 
 
@@ -93,7 +98,8 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
     # status is still pending
     _log_destroy_pending = True
 
-    def __init__(self, coro, *, loop=None, name=None, context=None):
+    def __init__(self, coro, *, loop=None, name=None, context=None,
+                 eager_start=False):
         super().__init__(loop=loop)
         if self._source_traceback:
             del self._source_traceback[-1]
@@ -117,6 +123,9 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
         else:
             self._context = context
 
+        if eager_start and self._loop.is_running():
+            self.__eager_start()
+        else:
             self._loop.call_soon(self.__step, context=self._context)
             _register_task(self)
 
@@ -250,6 +259,25 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
             self._num_cancels_requested -= 1
         return self._num_cancels_requested
 
+    def __eager_start(self):
+        prev_task = _swap_current_task(self._loop, self)
+        try:
+            _register_eager_task(self)
+            try:
+                self._context.run(self.__step_run_and_handle_result, None)
+            finally:
+                _unregister_eager_task(self)
+        finally:
+            try:
+                curtask = _swap_current_task(self._loop, prev_task)
+                assert curtask is self
+            finally:
+                if self.done():
+                    self._coro = None
+                    self = None  # Needed to break cycles when an exception occurs.
+                else:
+                    _register_task(self)
+
     def __step(self, exc=None):
         if self.done():
             raise exceptions.InvalidStateError(
@@ -258,11 +286,17 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
             if not isinstance(exc, exceptions.CancelledError):
                 exc = self._make_cancelled_error()
             self._must_cancel = False
-        coro = self._coro
         self._fut_waiter = None
 
         _enter_task(self._loop, self)
-        # Call either coro.throw(exc) or coro.send(None).
+        try:
+            self.__step_run_and_handle_result(exc)
+        finally:
+            _leave_task(self._loop, self)
+            self = None  # Needed to break cycles when an exception occurs.
+
+    def __step_run_and_handle_result(self, exc):
+        coro = self._coro
         try:
             if exc is None:
                 # We use the `send` method directly, because coroutines
@@ -334,7 +368,6 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
                 self._loop.call_soon(
                     self.__step, new_exc, context=self._context)
         finally:
-            _leave_task(self._loop, self)
             self = None  # Needed to break cycles when an exception occurs.
 
     def __wakeup(self, future):
@@ -897,8 +930,27 @@ def run_coroutine_threadsafe(coro, loop):
     return future
 
 
-# WeakSet containing all alive tasks.
+def create_eager_task_factory(custom_task_constructor):
-_all_tasks = weakref.WeakSet()
+
+    if "eager_start" not in inspect.signature(custom_task_constructor).parameters:
+        raise TypeError(
+            "Provided constructor does not support eager task execution")
+
+    def factory(loop, coro, *, name=None, context=None):
+        return custom_task_constructor(
+            coro, loop=loop, name=name, context=context, eager_start=True)
+
+
+    return factory
+
+eager_task_factory = create_eager_task_factory(Task)
+
+
+# Collectively these two sets hold references to the complete set of active
+# tasks. Eagerly executed tasks use a faster regular set as an optimization
+# but may graduate to a WeakSet if the task blocks on IO.
+_scheduled_tasks = weakref.WeakSet()
+_eager_tasks = set()
 
 # Dictionary containing tasks that are currently active in
 # all running event loops.  {EventLoop: Task}
@@ -906,8 +958,13 @@ _current_tasks = {}
 
 
 def _register_task(task):
-    """Register a new task in asyncio as executed by loop."""
+    """Register an asyncio Task scheduled to run on an event loop."""
-    _all_tasks.add(task)
+    _scheduled_tasks.add(task)
+
+
+def _register_eager_task(task):
+    """Register an asyncio Task about to be eagerly executed."""
+    _eager_tasks.add(task)
 
 
 def _enter_task(loop, task):
@@ -926,28 +983,49 @@ def _leave_task(loop, task):
     del _current_tasks[loop]
 
 
+def _swap_current_task(loop, task):
+    prev_task = _current_tasks.get(loop)
+    if task is None:
+        del _current_tasks[loop]
+    else:
+        _current_tasks[loop] = task
+    return prev_task
+
+
 def _unregister_task(task):
-    """Unregister a task."""
+    """Unregister a completed, scheduled Task."""
-    _all_tasks.discard(task)
+    _scheduled_tasks.discard(task)
+
+
+def _unregister_eager_task(task):
+    """Unregister a task which finished its first eager step."""
+    _eager_tasks.discard(task)
 
 
 _py_current_task = current_task
 _py_register_task = _register_task
+_py_register_eager_task = _register_eager_task
 _py_unregister_task = _unregister_task
+_py_unregister_eager_task = _unregister_eager_task
 _py_enter_task = _enter_task
 _py_leave_task = _leave_task
+_py_swap_current_task = _swap_current_task
 
 
 try:
-    from _asyncio import (_register_task, _unregister_task,
+    from _asyncio import (_register_task, _register_eager_task,
-                          _enter_task, _leave_task,
+                          _unregister_task, _unregister_eager_task,
-                          _all_tasks, _current_tasks,
+                          _enter_task, _leave_task, _swap_current_task,
+                          _scheduled_tasks, _eager_tasks, _current_tasks,
                           current_task)
 except ImportError:
     pass
 else:
     _c_current_task = current_task
     _c_register_task = _register_task
+    _c_register_eager_task = _register_eager_task
     _c_unregister_task = _unregister_task
+    _c_unregister_eager_task = _unregister_eager_task
     _c_enter_task = _enter_task
     _c_leave_task = _leave_task
+    _c_swap_current_task = _swap_current_task

Lib/test/test_asyncio/test_eager_task_factory.py

@@ -0,0 +1,344 @@
+"""Tests for base_events.py"""
+
+import asyncio
+import contextvars
+import gc
+import time
+import unittest
+
+from types import GenericAlias
+from unittest import mock
+from asyncio import base_events
+from asyncio import tasks
+from test.test_asyncio import utils as test_utils
+from test.test_asyncio.test_tasks import get_innermost_context
+from test import support
+
+MOCK_ANY = mock.ANY
+
+
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
+class EagerTaskFactoryLoopTests:
+
+    Task = None
+
+    def run_coro(self, coro):
+        """
+        Helper method to run the `coro` coroutine in the test event loop.
+        It helps with making sure the event loop is running before starting
+        to execute `coro`. This is important for testing the eager step
+        functionality, since an eager step is taken only if the event loop
+        is already running.
+        """
+
+        async def coro_runner():
+            self.assertTrue(asyncio.get_event_loop().is_running())
+            return await coro
+
+        return self.loop.run_until_complete(coro)
+
+    def setUp(self):
+        super().setUp()
+        self.loop = asyncio.new_event_loop()
+        self.eager_task_factory = asyncio.create_eager_task_factory(self.Task)
+        self.loop.set_task_factory(self.eager_task_factory)
+        self.set_event_loop(self.loop)
+
+    def test_eager_task_factory_set(self):
+        self.assertIsNotNone(self.eager_task_factory)
+        self.assertIs(self.loop.get_task_factory(), self.eager_task_factory)
+
+        async def noop(): pass
+
+        async def run():
+            t = self.loop.create_task(noop())
+            self.assertIsInstance(t, self.Task)
+            await t
+
+        self.run_coro(run())
+
+    def test_await_future_during_eager_step(self):
+
+        async def set_result(fut, val):
+            fut.set_result(val)
+
+        async def run():
+            fut = self.loop.create_future()
+            t = self.loop.create_task(set_result(fut, 'my message'))
+            # assert the eager step completed the task
+            self.assertTrue(t.done())
+            return await fut
+
+        self.assertEqual(self.run_coro(run()), 'my message')
+
+    def test_eager_completion(self):
+
+        async def coro():
+            return 'hello'
+
+        async def run():
+            t = self.loop.create_task(coro())
+            # assert the eager step completed the task
+            self.assertTrue(t.done())
+            return await t
+
+        self.assertEqual(self.run_coro(run()), 'hello')
+
+    def test_block_after_eager_step(self):
+
+        async def coro():
+            await asyncio.sleep(0.1)
+            return 'finished after blocking'
+
+        async def run():
+            t = self.loop.create_task(coro())
+            self.assertFalse(t.done())
+            result = await t
+            self.assertTrue(t.done())
+            return result
+
+        self.assertEqual(self.run_coro(run()), 'finished after blocking')
+
+    def test_cancellation_after_eager_completion(self):
+
+        async def coro():
+            return 'finished without blocking'
+
+        async def run():
+            t = self.loop.create_task(coro())
+            t.cancel()
+            result = await t
+            # finished task can't be cancelled
+            self.assertFalse(t.cancelled())
+            return result
+
+        self.assertEqual(self.run_coro(run()), 'finished without blocking')
+
+    def test_cancellation_after_eager_step_blocks(self):
+
+        async def coro():
+            await asyncio.sleep(0.1)
+            return 'finished after blocking'
+
+        async def run():
+            t = self.loop.create_task(coro())
+            t.cancel('cancellation message')
+            self.assertGreater(t.cancelling(), 0)
+            result = await t
+
+        with self.assertRaises(asyncio.CancelledError) as cm:
+            self.run_coro(run())
+
+        self.assertEqual('cancellation message', cm.exception.args[0])
+
+    def test_current_task(self):
+        captured_current_task = None
+
+        async def coro():
+            nonlocal captured_current_task
+            captured_current_task = asyncio.current_task()
+            # verify the task before and after blocking is identical
+            await asyncio.sleep(0.1)
+            self.assertIs(asyncio.current_task(), captured_current_task)
+
+        async def run():
+            t = self.loop.create_task(coro())
+            self.assertIs(captured_current_task, t)
+            await t
+
+        self.run_coro(run())
+        captured_current_task = None
+
+    def test_all_tasks_with_eager_completion(self):
+        captured_all_tasks = None
+
+        async def coro():
+            nonlocal captured_all_tasks
+            captured_all_tasks = asyncio.all_tasks()
+
+        async def run():
+            t = self.loop.create_task(coro())
+            self.assertIn(t, captured_all_tasks)
+            self.assertNotIn(t, asyncio.all_tasks())
+
+        self.run_coro(run())
+
+    def test_all_tasks_with_blocking(self):
+        captured_eager_all_tasks = None
+
+        async def coro(fut1, fut2):
+            nonlocal captured_eager_all_tasks
+            captured_eager_all_tasks = asyncio.all_tasks()
+            await fut1
+            fut2.set_result(None)
+
+        async def run():
+            fut1 = self.loop.create_future()
+            fut2 = self.loop.create_future()
+            t = self.loop.create_task(coro(fut1, fut2))
+            self.assertIn(t, captured_eager_all_tasks)
+            self.assertIn(t, asyncio.all_tasks())
+            fut1.set_result(None)
+            await fut2
+            self.assertNotIn(t, asyncio.all_tasks())
+
+        self.run_coro(run())
+
+    def test_context_vars(self):
+        cv = contextvars.ContextVar('cv', default=0)
+
+        coro_first_step_ran = False
+        coro_second_step_ran = False
+
+        async def coro():
+            nonlocal coro_first_step_ran
+            nonlocal coro_second_step_ran
+            self.assertEqual(cv.get(), 1)
+            cv.set(2)
+            self.assertEqual(cv.get(), 2)
+            coro_first_step_ran = True
+            await asyncio.sleep(0.1)
+            self.assertEqual(cv.get(), 2)
+            cv.set(3)
+            self.assertEqual(cv.get(), 3)
+            coro_second_step_ran = True
+
+        async def run():
+            cv.set(1)
+            t = self.loop.create_task(coro())
+            self.assertTrue(coro_first_step_ran)
+            self.assertFalse(coro_second_step_ran)
+            self.assertEqual(cv.get(), 1)
+            await t
+            self.assertTrue(coro_second_step_ran)
+            self.assertEqual(cv.get(), 1)
+
+        self.run_coro(run())
+
+
+class PyEagerTaskFactoryLoopTests(EagerTaskFactoryLoopTests, test_utils.TestCase):
+    Task = tasks._PyTask
+
+
+@unittest.skipUnless(hasattr(tasks, '_CTask'),
+                     'requires the C _asyncio module')
+class CEagerTaskFactoryLoopTests(EagerTaskFactoryLoopTests, test_utils.TestCase):
+    Task = getattr(tasks, '_CTask', None)
+
+
+class AsyncTaskCounter:
+    def __init__(self, loop, *, task_class, eager):
+        self.suspense_count = 0
+        self.task_count = 0
+
+        def CountingTask(*args, eager_start=False, **kwargs):
+            if not eager_start:
+                self.task_count += 1
+            kwargs["eager_start"] = eager_start
+            return task_class(*args, **kwargs)
+
+        if eager:
+            factory = asyncio.create_eager_task_factory(CountingTask)
+        else:
+            def factory(loop, coro, **kwargs):
+                return CountingTask(coro, loop=loop, **kwargs)
+        loop.set_task_factory(factory)
+
+    def get(self):
+        return self.task_count
+
+
+async def awaitable_chain(depth):
+    if depth == 0:
+        return 0
+    return 1 + await awaitable_chain(depth - 1)
+
+
+async def recursive_taskgroups(width, depth):
+    if depth == 0:
+        return
+
+    async with asyncio.TaskGroup() as tg:
+        futures = [
+            tg.create_task(recursive_taskgroups(width, depth - 1))
+            for _ in range(width)
+        ]
+
+
+async def recursive_gather(width, depth):
+    if depth == 0:
+        return
+
+    await asyncio.gather(
+        *[recursive_gather(width, depth - 1) for _ in range(width)]
+    )
+
+
+class BaseTaskCountingTests:
+
+    Task = None
+    eager = None
+    expected_task_count = None
+
+    def setUp(self):
+        super().setUp()
+        self.loop = asyncio.new_event_loop()
+        self.counter = AsyncTaskCounter(self.loop, task_class=self.Task, eager=self.eager)
+        self.set_event_loop(self.loop)
+
+    def test_awaitables_chain(self):
+        observed_depth = self.loop.run_until_complete(awaitable_chain(100))
+        self.assertEqual(observed_depth, 100)
+        self.assertEqual(self.counter.get(), 0 if self.eager else 1)
+
+    def test_recursive_taskgroups(self):
+        num_tasks = self.loop.run_until_complete(recursive_taskgroups(5, 4))
+        self.assertEqual(self.counter.get(), self.expected_task_count)
+
+    def test_recursive_gather(self):
+        self.loop.run_until_complete(recursive_gather(5, 4))
+        self.assertEqual(self.counter.get(), self.expected_task_count)
+
+
+class BaseNonEagerTaskFactoryTests(BaseTaskCountingTests):
+    eager = False
+    expected_task_count = 781  # 1 + 5 + 5^2 + 5^3 + 5^4
+
+
+class BaseEagerTaskFactoryTests(BaseTaskCountingTests):
+    eager = True
+    expected_task_count = 0
+
+
+class NonEagerTests(BaseNonEagerTaskFactoryTests, test_utils.TestCase):
+    Task = asyncio.Task
+
+
+class EagerTests(BaseEagerTaskFactoryTests, test_utils.TestCase):
+    Task = asyncio.Task
+
+
+class NonEagerPyTaskTests(BaseNonEagerTaskFactoryTests, test_utils.TestCase):
+    Task = tasks._PyTask
+
+
+class EagerPyTaskTests(BaseEagerTaskFactoryTests, test_utils.TestCase):
+    Task = tasks._PyTask
+
+
+@unittest.skipUnless(hasattr(tasks, '_CTask'),
+                     'requires the C _asyncio module')
+class NonEagerCTaskTests(BaseNonEagerTaskFactoryTests, test_utils.TestCase):
+    Task = getattr(tasks, '_CTask', None)
+
+
+@unittest.skipUnless(hasattr(tasks, '_CTask'),
+                     'requires the C _asyncio module')
+class EagerCTaskTests(BaseEagerTaskFactoryTests, test_utils.TestCase):
+    Task = getattr(tasks, '_CTask', None)
+
+if __name__ == '__main__':
+    unittest.main()

Misc/NEWS.d/next/Library/2023-03-15-12-18-07.gh-issue-97696.DtnpIC.rst

@@ -0,0 +1,6 @@
+Implemented an eager task factory in asyncio.
+When used as a task factory on an event loop, it performs eager execution of
+coroutines. Coroutines that are able to complete synchronously (e.g. return or
+raise without blocking) are returned immediately as a finished task, and the
+task is never scheduled to the event loop. If the coroutine blocks, the
+(pending) task is scheduled and returned.

Modules/_asynciomodule.c

@@ -8,6 +8,7 @@
 #include "pycore_runtime_init.h"  // _Py_ID()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "structmember.h"         // PyMemberDef
+#include "cpython/context.h"
 #include <stddef.h>               // offsetof()
 
 
@@ -31,8 +32,11 @@ typedef struct {
        all running event loops.  {EventLoop: Task} */
     PyObject *current_tasks;
 
-    /* WeakSet containing all alive tasks. */
+    /* WeakSet containing all tasks scheduled to run on event loops. */
-    PyObject *all_tasks;
+    PyObject *scheduled_tasks;
+
+    /* Set containing all eagerly executing tasks. */
+    PyObject *eager_tasks;
 
     /* An isinstance type cache for the 'is_coroutine()' function. */
     PyObject *iscoroutine_typecache;
@@ -156,6 +160,9 @@ class _asyncio.Future "FutureObj *" "&Future_Type"
 /* Get FutureIter from Future */
 static PyObject * future_new_iter(PyObject *);
 
+static PyObject *
+task_step_handle_result_impl(asyncio_state *state, TaskObj *task, PyObject *result);
+
 
 static int
 _is_coroutine(asyncio_state *state, PyObject *coro)
@@ -1830,6 +1837,7 @@ class _asyncio.Task "TaskObj *" "&Task_Type"
 static int task_call_step_soon(asyncio_state *state, TaskObj *, PyObject *);
 static PyObject * task_wakeup(TaskObj *, PyObject *);
 static PyObject * task_step(asyncio_state *, TaskObj *, PyObject *);
+static int task_eager_start(asyncio_state *state, TaskObj *task);
 
 /* ----- Task._step wrapper */
 
@@ -1940,7 +1948,7 @@ static  PyMethodDef TaskWakeupDef = {
 static int
 register_task(asyncio_state *state, PyObject *task)
 {
-    PyObject *res = PyObject_CallMethodOneArg(state->all_tasks,
+    PyObject *res = PyObject_CallMethodOneArg(state->scheduled_tasks,
                                                  &_Py_ID(add), task);
     if (res == NULL) {
         return -1;
@@ -1949,11 +1957,16 @@ register_task(asyncio_state *state, PyObject *task)
     return 0;
 }
 
+static int
+register_eager_task(asyncio_state *state, PyObject *task)
+{
+    return PySet_Add(state->eager_tasks, task);
+}
 
 static int
 unregister_task(asyncio_state *state, PyObject *task)
 {
-    PyObject *res = PyObject_CallMethodOneArg(state->all_tasks,
+    PyObject *res = PyObject_CallMethodOneArg(state->scheduled_tasks,
                                      &_Py_ID(discard), task);
     if (res == NULL) {
         return -1;
@@ -1962,6 +1975,11 @@ unregister_task(asyncio_state *state, PyObject *task)
     return 0;
 }
 
+static int
+unregister_eager_task(asyncio_state *state, PyObject *task)
+{
+    return PySet_Discard(state->eager_tasks, task);
+}
 
 static int
 enter_task(asyncio_state *state, PyObject *loop, PyObject *task)
@@ -2015,6 +2033,54 @@ leave_task(asyncio_state *state, PyObject *loop, PyObject *task)
     return _PyDict_DelItem_KnownHash(state->current_tasks, loop, hash);
 }
 
+static PyObject *
+swap_current_task(asyncio_state *state, PyObject *loop, PyObject *task)
+{
+    PyObject *prev_task;
+    Py_hash_t hash;
+    hash = PyObject_Hash(loop);
+    if (hash == -1) {
+        return NULL;
+    }
+
+    prev_task = _PyDict_GetItem_KnownHash(state->current_tasks, loop, hash);
+    if (prev_task == NULL) {
+        if (PyErr_Occurred()) {
+            return NULL;
+        }
+        prev_task = Py_None;
+    }
+
+    if (task == Py_None) {
+        if (_PyDict_DelItem_KnownHash(state->current_tasks, loop, hash) == -1) {
+            return NULL;
+        }
+    } else {
+        if (_PyDict_SetItem_KnownHash(state->current_tasks, loop, task, hash) == -1) {
+            return NULL;
+        }
+    }
+
+    Py_INCREF(prev_task);
+
+    return prev_task;
+}
+
+static int
+is_loop_running(PyObject *loop)
+{
+    PyObject *func = PyObject_GetAttr(loop, &_Py_ID(is_running));
+    if (func == NULL) {
+        PyErr_Format(PyExc_TypeError, "Loop missing is_running()");
+        return -1;
+    }
+    PyObject *res = PyObject_CallNoArgs(func);
+    int retval = Py_IsTrue(res);
+    Py_DECREF(func);
+    Py_DECREF(res);
+    return !!retval;
+}
+
 /* ----- Task */
 
 /*[clinic input]
@@ -2025,15 +2091,16 @@ _asyncio.Task.__init__
     loop: object = None
     name: object = None
     context: object = None
+    eager_start: bool = False
 
 A coroutine wrapped in a Future.
 [clinic start generated code]*/
 
 static int
 _asyncio_Task___init___impl(TaskObj *self, PyObject *coro, PyObject *loop,
-                            PyObject *name, PyObject *context)
+                            PyObject *name, PyObject *context,
-/*[clinic end generated code: output=49ac96fe33d0e5c7 input=924522490c8ce825]*/
+                            int eager_start)
-
+/*[clinic end generated code: output=7aced2d27836f1a1 input=18e3f113a51b829d]*/
 {
     if (future_init((FutureObj*)self, loop)) {
         return -1;
@@ -2083,6 +2150,19 @@ _asyncio_Task___init___impl(TaskObj *self, PyObject *coro, PyObject *loop,
         return -1;
     }
 
+    if (eager_start) {
+        int loop_running = is_loop_running(self->task_loop);
+        if (loop_running == -1) {
+            return -1;
+        }
+        if (loop_running) {
+            if (task_eager_start(state, self)) {
+                return -1;
+            }
+            return 0;
+        }
+    }
+
     if (task_call_step_soon(state, self, NULL)) {
         return -1;
     }
@@ -2831,6 +2911,20 @@ task_step_impl(asyncio_state *state, TaskObj *task, PyObject *exc)
         Py_RETURN_NONE;
     }
 
+    PyObject *ret = task_step_handle_result_impl(state, task, result);
+    return ret;
+
+fail:
+    return NULL;
+}
+
+
+static PyObject *
+task_step_handle_result_impl(asyncio_state *state, TaskObj *task, PyObject *result)
+{
+    int res;
+    PyObject *o;
+
     if (result == (PyObject*)task) {
         /* We have a task that wants to await on itself */
         goto self_await;
@@ -3062,6 +3156,65 @@ task_step(asyncio_state *state, TaskObj *task, PyObject *exc)
     }
 }
 
+static int
+task_eager_start(asyncio_state *state, TaskObj *task)
+{
+    assert(task != NULL);
+    PyObject *prevtask = swap_current_task(state, task->task_loop, (PyObject *)task);
+    if (prevtask == NULL) {
+        return -1;
+    }
+
+    if (register_eager_task(state, (PyObject *)task) == -1) {
+        Py_DECREF(prevtask);
+        return -1;
+    }
+
+    if (PyContext_Enter(task->task_context) == -1) {
+        Py_DECREF(prevtask);
+        return -1;
+    }
+
+    int retval = 0;
+
+    PyObject *stepres = task_step_impl(state, task, NULL);
+    if (stepres == NULL) {
+        PyObject *exc = PyErr_GetRaisedException();
+        _PyErr_ChainExceptions1(exc);
+        retval = -1;
+    } else {
+        Py_DECREF(stepres);
+    }
+
+    PyObject *curtask = swap_current_task(state, task->task_loop, prevtask);
+    Py_DECREF(prevtask);
+    if (curtask == NULL) {
+        retval = -1;
+    } else {
+        assert(curtask == (PyObject *)task);
+        Py_DECREF(curtask);
+    }
+
+    if (unregister_eager_task(state, (PyObject *)task) == -1) {
+        retval = -1;
+    }
+
+    if (PyContext_Exit(task->task_context) == -1) {
+        retval = -1;
+    }
+
+    if (task->task_state == STATE_PENDING) {
+        if (register_task(state, (PyObject *)task) == -1) {
+            retval = -1;
+        }
+    } else {
+        // This seems to really help performance on pyperformance benchmarks
+        Py_CLEAR(task->task_coro);
+    }
+
+    return retval;
+}
+
 static PyObject *
 task_wakeup(TaskObj *task, PyObject *o)
 {
@@ -3225,6 +3378,27 @@ _asyncio__register_task_impl(PyObject *module, PyObject *task)
     Py_RETURN_NONE;
 }
 
+/*[clinic input]
+_asyncio._register_eager_task
+
+    task: object
+
+Register a new task in asyncio as executed by loop.
+
+Returns None.
+[clinic start generated code]*/
+
+static PyObject *
+_asyncio__register_eager_task_impl(PyObject *module, PyObject *task)
+/*[clinic end generated code: output=dfe1d45367c73f1a input=237f684683398c51]*/
+{
+    asyncio_state *state = get_asyncio_state(module);
+    if (register_eager_task(state, task) < 0) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 
 /*[clinic input]
 _asyncio._unregister_task
@@ -3247,6 +3421,27 @@ _asyncio__unregister_task_impl(PyObject *module, PyObject *task)
     Py_RETURN_NONE;
 }
 
+/*[clinic input]
+_asyncio._unregister_eager_task
+
+    task: object
+
+Unregister a task.
+
+Returns None.
+[clinic start generated code]*/
+
+static PyObject *
+_asyncio__unregister_eager_task_impl(PyObject *module, PyObject *task)
+/*[clinic end generated code: output=a426922bd07f23d1 input=9d07401ef14ee048]*/
+{
+    asyncio_state *state = get_asyncio_state(module);
+    if (unregister_eager_task(state, task) < 0) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 
 /*[clinic input]
 _asyncio._enter_task
@@ -3298,6 +3493,27 @@ _asyncio__leave_task_impl(PyObject *module, PyObject *loop, PyObject *task)
 }
 
 
+/*[clinic input]
+_asyncio._swap_current_task
+
+    loop: object
+    task: object
+
+Temporarily swap in the supplied task and return the original one (or None).
+
+This is intended for use during eager coroutine execution.
+
+[clinic start generated code]*/
+
+static PyObject *
+_asyncio__swap_current_task_impl(PyObject *module, PyObject *loop,
+                                 PyObject *task)
+/*[clinic end generated code: output=9f88de958df74c7e input=c9c72208d3d38b6c]*/
+{
+    return swap_current_task(get_asyncio_state(module), loop, task);
+}
+
+
 /*[clinic input]
 _asyncio.current_task
 
@@ -3379,7 +3595,8 @@ module_traverse(PyObject *mod, visitproc visit, void *arg)
     Py_VISIT(state->asyncio_InvalidStateError);
     Py_VISIT(state->asyncio_CancelledError);
 
-    Py_VISIT(state->all_tasks);
+    Py_VISIT(state->scheduled_tasks);
+    Py_VISIT(state->eager_tasks);
     Py_VISIT(state->current_tasks);
     Py_VISIT(state->iscoroutine_typecache);
 
@@ -3416,7 +3633,8 @@ module_clear(PyObject *mod)
     Py_CLEAR(state->asyncio_InvalidStateError);
     Py_CLEAR(state->asyncio_CancelledError);
 
-    Py_CLEAR(state->all_tasks);
+    Py_CLEAR(state->scheduled_tasks);
+    Py_CLEAR(state->eager_tasks);
     Py_CLEAR(state->current_tasks);
     Py_CLEAR(state->iscoroutine_typecache);
 
@@ -3496,9 +3714,14 @@ module_init(asyncio_state *state)
     PyObject *weak_set;
     WITH_MOD("weakref")
     GET_MOD_ATTR(weak_set, "WeakSet");
-    state->all_tasks = PyObject_CallNoArgs(weak_set);
+    state->scheduled_tasks = PyObject_CallNoArgs(weak_set);
     Py_CLEAR(weak_set);
-    if (state->all_tasks == NULL) {
+    if (state->scheduled_tasks == NULL) {
+        goto fail;
+    }
+
+    state->eager_tasks = PySet_New(NULL);
+    if (state->eager_tasks == NULL) {
         goto fail;
     }
 
@@ -3522,9 +3745,12 @@ static PyMethodDef asyncio_methods[] = {
     _ASYNCIO__GET_RUNNING_LOOP_METHODDEF
     _ASYNCIO__SET_RUNNING_LOOP_METHODDEF
     _ASYNCIO__REGISTER_TASK_METHODDEF
+    _ASYNCIO__REGISTER_EAGER_TASK_METHODDEF
     _ASYNCIO__UNREGISTER_TASK_METHODDEF
+    _ASYNCIO__UNREGISTER_EAGER_TASK_METHODDEF
     _ASYNCIO__ENTER_TASK_METHODDEF
     _ASYNCIO__LEAVE_TASK_METHODDEF
+    _ASYNCIO__SWAP_CURRENT_TASK_METHODDEF
     {NULL, NULL}
 };
 
@@ -3561,7 +3787,11 @@ module_exec(PyObject *mod)
         return -1;
     }
 
-    if (PyModule_AddObjectRef(mod, "_all_tasks", state->all_tasks) < 0) {
+    if (PyModule_AddObjectRef(mod, "_scheduled_tasks", state->scheduled_tasks) < 0) {
+        return -1;
+    }
+
+    if (PyModule_AddObjectRef(mod, "_eager_tasks", state->eager_tasks) < 0) {
         return -1;
     }
 

Modules/clinic/_asynciomodule.c.h

@@ -482,14 +482,15 @@ _asyncio_Future__make_cancelled_error(FutureObj *self, PyObject *Py_UNUSED(ignor
 }
 
 PyDoc_STRVAR(_asyncio_Task___init____doc__,
-"Task(coro, *, loop=None, name=None, context=None)\n"
+"Task(coro, *, loop=None, name=None, context=None, eager_start=False)\n"
 "--\n"
 "\n"
 "A coroutine wrapped in a Future.");
 
 static int
 _asyncio_Task___init___impl(TaskObj *self, PyObject *coro, PyObject *loop,
-                            PyObject *name, PyObject *context);
+                            PyObject *name, PyObject *context,
+                            int eager_start);
 
 static int
 _asyncio_Task___init__(PyObject *self, PyObject *args, PyObject *kwargs)
@@ -497,14 +498,14 @@ _asyncio_Task___init__(PyObject *self, PyObject *args, PyObject *kwargs)
     int return_value = -1;
     #if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
 
-    #define NUM_KEYWORDS 4
+    #define NUM_KEYWORDS 5
     static struct {
         PyGC_Head _this_is_not_used;
         PyObject_VAR_HEAD
         PyObject *ob_item[NUM_KEYWORDS];
     } _kwtuple = {
         .ob_base = PyVarObject_HEAD_INIT(&PyTuple_Type, NUM_KEYWORDS)
-        .ob_item = { &_Py_ID(coro), &_Py_ID(loop), &_Py_ID(name), &_Py_ID(context), },
+        .ob_item = { &_Py_ID(coro), &_Py_ID(loop), &_Py_ID(name), &_Py_ID(context), &_Py_ID(eager_start), },
     };
     #undef NUM_KEYWORDS
     #define KWTUPLE (&_kwtuple.ob_base.ob_base)
@@ -513,14 +514,14 @@ _asyncio_Task___init__(PyObject *self, PyObject *args, PyObject *kwargs)
     #  define KWTUPLE NULL
     #endif  // !Py_BUILD_CORE
 
-    static const char * const _keywords[] = {"coro", "loop", "name", "context", NULL};
+    static const char * const _keywords[] = {"coro", "loop", "name", "context", "eager_start", NULL};
     static _PyArg_Parser _parser = {
         .keywords = _keywords,
         .fname = "Task",
         .kwtuple = KWTUPLE,
     };
     #undef KWTUPLE
-    PyObject *argsbuf[4];
+    PyObject *argsbuf[5];
     PyObject * const *fastargs;
     Py_ssize_t nargs = PyTuple_GET_SIZE(args);
     Py_ssize_t noptargs = nargs + (kwargs ? PyDict_GET_SIZE(kwargs) : 0) - 1;
@@ -528,6 +529,7 @@ _asyncio_Task___init__(PyObject *self, PyObject *args, PyObject *kwargs)
     PyObject *loop = Py_None;
     PyObject *name = Py_None;
     PyObject *context = Py_None;
+    int eager_start = 0;
 
     fastargs = _PyArg_UnpackKeywords(_PyTuple_CAST(args)->ob_item, nargs, kwargs, NULL, &_parser, 1, 1, 0, argsbuf);
     if (!fastargs) {
@@ -549,9 +551,18 @@ _asyncio_Task___init__(PyObject *self, PyObject *args, PyObject *kwargs)
             goto skip_optional_kwonly;
         }
     }
+    if (fastargs[3]) {
         context = fastargs[3];
+        if (!--noptargs) {
+            goto skip_optional_kwonly;
+        }
+    }
+    eager_start = PyObject_IsTrue(fastargs[4]);
+    if (eager_start < 0) {
+        goto exit;
+    }
 skip_optional_kwonly:
-    return_value = _asyncio_Task___init___impl((TaskObj *)self, coro, loop, name, context);
+    return_value = _asyncio_Task___init___impl((TaskObj *)self, coro, loop, name, context, eager_start);
 
 exit:
     return return_value;
@@ -1064,6 +1075,63 @@ exit:
     return return_value;
 }
 
+PyDoc_STRVAR(_asyncio__register_eager_task__doc__,
+"_register_eager_task($module, /, task)\n"
+"--\n"
+"\n"
+"Register a new task in asyncio as executed by loop.\n"
+"\n"
+"Returns None.");
+
+#define _ASYNCIO__REGISTER_EAGER_TASK_METHODDEF    \
+    {"_register_eager_task", _PyCFunction_CAST(_asyncio__register_eager_task), METH_FASTCALL|METH_KEYWORDS, _asyncio__register_eager_task__doc__},
+
+static PyObject *
+_asyncio__register_eager_task_impl(PyObject *module, PyObject *task);
+
+static PyObject *
+_asyncio__register_eager_task(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    #if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
+
+    #define NUM_KEYWORDS 1
+    static struct {
+        PyGC_Head _this_is_not_used;
+        PyObject_VAR_HEAD
+        PyObject *ob_item[NUM_KEYWORDS];
+    } _kwtuple = {
+        .ob_base = PyVarObject_HEAD_INIT(&PyTuple_Type, NUM_KEYWORDS)
+        .ob_item = { &_Py_ID(task), },
+    };
+    #undef NUM_KEYWORDS
+    #define KWTUPLE (&_kwtuple.ob_base.ob_base)
+
+    #else  // !Py_BUILD_CORE
+    #  define KWTUPLE NULL
+    #endif  // !Py_BUILD_CORE
+
+    static const char * const _keywords[] = {"task", NULL};
+    static _PyArg_Parser _parser = {
+        .keywords = _keywords,
+        .fname = "_register_eager_task",
+        .kwtuple = KWTUPLE,
+    };
+    #undef KWTUPLE
+    PyObject *argsbuf[1];
+    PyObject *task;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    task = args[0];
+    return_value = _asyncio__register_eager_task_impl(module, task);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(_asyncio__unregister_task__doc__,
 "_unregister_task($module, /, task)\n"
 "--\n"
@@ -1121,6 +1189,63 @@ exit:
     return return_value;
 }
 
+PyDoc_STRVAR(_asyncio__unregister_eager_task__doc__,
+"_unregister_eager_task($module, /, task)\n"
+"--\n"
+"\n"
+"Unregister a task.\n"
+"\n"
+"Returns None.");
+
+#define _ASYNCIO__UNREGISTER_EAGER_TASK_METHODDEF    \
+    {"_unregister_eager_task", _PyCFunction_CAST(_asyncio__unregister_eager_task), METH_FASTCALL|METH_KEYWORDS, _asyncio__unregister_eager_task__doc__},
+
+static PyObject *
+_asyncio__unregister_eager_task_impl(PyObject *module, PyObject *task);
+
+static PyObject *
+_asyncio__unregister_eager_task(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    #if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
+
+    #define NUM_KEYWORDS 1
+    static struct {
+        PyGC_Head _this_is_not_used;
+        PyObject_VAR_HEAD
+        PyObject *ob_item[NUM_KEYWORDS];
+    } _kwtuple = {
+        .ob_base = PyVarObject_HEAD_INIT(&PyTuple_Type, NUM_KEYWORDS)
+        .ob_item = { &_Py_ID(task), },
+    };
+    #undef NUM_KEYWORDS
+    #define KWTUPLE (&_kwtuple.ob_base.ob_base)
+
+    #else  // !Py_BUILD_CORE
+    #  define KWTUPLE NULL
+    #endif  // !Py_BUILD_CORE
+
+    static const char * const _keywords[] = {"task", NULL};
+    static _PyArg_Parser _parser = {
+        .keywords = _keywords,
+        .fname = "_unregister_eager_task",
+        .kwtuple = KWTUPLE,
+    };
+    #undef KWTUPLE
+    PyObject *argsbuf[1];
+    PyObject *task;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    task = args[0];
+    return_value = _asyncio__unregister_eager_task_impl(module, task);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(_asyncio__enter_task__doc__,
 "_enter_task($module, /, loop, task)\n"
 "--\n"
@@ -1243,6 +1368,66 @@ exit:
     return return_value;
 }
 
+PyDoc_STRVAR(_asyncio__swap_current_task__doc__,
+"_swap_current_task($module, /, loop, task)\n"
+"--\n"
+"\n"
+"Temporarily swap in the supplied task and return the original one (or None).\n"
+"\n"
+"This is intended for use during eager coroutine execution.");
+
+#define _ASYNCIO__SWAP_CURRENT_TASK_METHODDEF    \
+    {"_swap_current_task", _PyCFunction_CAST(_asyncio__swap_current_task), METH_FASTCALL|METH_KEYWORDS, _asyncio__swap_current_task__doc__},
+
+static PyObject *
+_asyncio__swap_current_task_impl(PyObject *module, PyObject *loop,
+                                 PyObject *task);
+
+static PyObject *
+_asyncio__swap_current_task(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    #if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
+
+    #define NUM_KEYWORDS 2
+    static struct {
+        PyGC_Head _this_is_not_used;
+        PyObject_VAR_HEAD
+        PyObject *ob_item[NUM_KEYWORDS];
+    } _kwtuple = {
+        .ob_base = PyVarObject_HEAD_INIT(&PyTuple_Type, NUM_KEYWORDS)
+        .ob_item = { &_Py_ID(loop), &_Py_ID(task), },
+    };
+    #undef NUM_KEYWORDS
+    #define KWTUPLE (&_kwtuple.ob_base.ob_base)
+
+    #else  // !Py_BUILD_CORE
+    #  define KWTUPLE NULL
+    #endif  // !Py_BUILD_CORE
+
+    static const char * const _keywords[] = {"loop", "task", NULL};
+    static _PyArg_Parser _parser = {
+        .keywords = _keywords,
+        .fname = "_swap_current_task",
+        .kwtuple = KWTUPLE,
+    };
+    #undef KWTUPLE
+    PyObject *argsbuf[2];
+    PyObject *loop;
+    PyObject *task;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 2, 2, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    loop = args[0];
+    task = args[1];
+    return_value = _asyncio__swap_current_task_impl(module, loop, task);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(_asyncio_current_task__doc__,
 "current_task($module, /, loop=None)\n"
 "--\n"
@@ -1302,4 +1487,4 @@ skip_optional_pos:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=00f494214f2fd008 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=6b0e283177b07639 input=a9049054013a1b77]*/