May 1, 2023 · Mar 20, 2023 · Mar 20, 2023 · Mar 20, 2023 · Mar 22, 2023 · Mar 22, 2023
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
      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
 ===========================

diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst
 * 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
 ========================
diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h
        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)
        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)
diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h
diff --git a/Lib/asyncio/base_tasks.py b/Lib/asyncio/base_tasks.py

    info.insert(1, 'name=%r' % task.get_name())

    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}')
        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}>')

    return info


diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
    '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',
 )

    """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
    # thread while we do so. 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.
    # capturing the set of eager tasks first, so if an eager task "graduates"
    # to a regular task in another thread, we don't risk missing it.
    eager_tasks = list(_eager_tasks)
    # Looping over the WeakSet isn't safe as it can be updated from another
    # 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 intasks
    return {t for t initertools.chain(scheduled_tasks, eager_tasks)
            if futures._get_loop(t) is loop and not t.done()}


    # 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]
        else:
            self._context = context

        self._loop.call_soon(self.__step, context=self._context)
        _register_task(self)
        if eager_start and self._loop.is_running():
            self.__eager_start()
        else:
            self._loop.call_soon(self.__step, context=self._context)
            _register_task(self)

    def __del__(self):
        if self._state == futures._PENDING and self._log_destroy_pending:
            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(
            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
                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):
    return future


 # WeakSet containing all alive tasks.
 _all_tasks = weakref.WeakSet()
 def create_eager_task_factory(custom_task_constructor):

    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}
 _current_tasks = {}


 def _register_task(task):
    """Register a new task in asyncio as executed by loop."""
    _all_tasks.add(task)
    """Register an asyncio Task scheduled to run on an event loop."""
    _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):
    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."""
    _all_tasks.discard(task)
    """Unregister a completed, scheduled 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,
                          _enter_task, _leave_task,
                          _all_tasks, _current_tasks,
    from _asyncio import (_register_task, _register_eager_task,
                          _unregister_task, _unregister_eager_task,
                          _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
Original file line number	Diff line number	Diff line change
Expand Up		@@ -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
		===========================

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -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
		========================
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -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)
Expand DownExpand Up		@@ -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)
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -15,11 +15,13 @@ def _task_repr_info(task):

		info.insert(1, 'name=%r' % task.get_name())

		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}')
		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}>')

		return info


Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -6,6 +6,7 @@
		'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',
		)

Expand DownExpand Up		@@ -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
		# thread while we do so. 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.
		# capturing the set of eager tasks first, so if an eager task "graduates"
		# to a regular task in another thread, we don't risk missing it.
		eager_tasks = list(_eager_tasks)
		# Looping over the WeakSet isn't safe as it can be updated from another
		# 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 intasks
		return {t for t initertools.chain(scheduled_tasks, eager_tasks)
		if futures._get_loop(t) is loop and not t.done()}


Expand DownExpand Up		@@ -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]
Expand All		@@ -117,8 +123,11 @@ def __init__(self, coro, *, loop=None, name=None, context=None):
		else:
		self._context = context

		self._loop.call_soon(self.__step, context=self._context)
		_register_task(self)
		if eager_start and self._loop.is_running():
		self.__eager_start()
		else:
		self._loop.call_soon(self.__step, context=self._context)
		_register_task(self)

		def __del__(self):
		if self._state == futures._PENDING and self._log_destroy_pending:
Expand DownExpand Up		@@ -250,6 +259,25 @@ def uncancel(self):
		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(
Expand All		@@ -258,11 +286,17 @@ def __step(self, exc=None):
		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
Expand DownExpand Up		@@ -334,7 +368,6 @@ def __step(self, exc=None):
		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):
Expand DownExpand Up		@@ -897,17 +930,41 @@ def callback():
		return future


		# WeakSet containing all alive tasks.
		_all_tasks = weakref.WeakSet()
		def create_eager_task_factory(custom_task_constructor):

		if "eager_start" not in inspect.signature(custom_task_constructor).parameters:
itamaro marked this conversation as resolved. Show resolvedHide resolved
		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}
		_current_tasks = {}


		def _register_task(task):
		"""Register a new task in asyncio as executed by loop."""
		_all_tasks.add(task)
		"""Register an asyncio Task scheduled to run on an event loop."""
		_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):
Expand All		@@ -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."""
		_all_tasks.discard(task)
		"""Unregister a completed, scheduled 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,
		_enter_task, _leave_task,
		_all_tasks, _current_tasks,
		from _asyncio import (_register_task, _register_eager_task,
		_unregister_task, _unregister_eager_task,
		_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