"""Support for tasks, coroutines and the scheduler."""
'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED',
'wait', 'wait_for', 'as_completed', 'sleep',
'gather', 'shield', 'ensure_future', 'run_coroutine_threadsafe',
'current_task', 'all_tasks',
'_register_task', '_unregister_task', '_enter_task', '_leave_task',
import concurrent.futures
from .coroutines import _is_coroutine
# Helper to generate new task names
# This uses itertools.count() instead of a "+= 1" operation because the latter
# is not thread safe. See bpo-11866 for a longer explanation.
_task_name_counter = itertools.count(1).__next__
def current_task(loop=None):
"""Return a currently executed task."""
loop = events.get_running_loop()
return _current_tasks.get(loop)
def all_tasks(loop=None):
"""Return a set of all tasks for the loop."""
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
if futures._get_loop(t) is loop and not t.done()}
def _all_tasks_compat(loop=None):
# Different from "all_task()" by returning *all* Tasks, including
# the completed ones. Used to implement deprecated "Tasks.all_task()"
loop = events.get_event_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
return {t for t in tasks if futures._get_loop(t) is loop}
def _set_task_name(task, name):
class Task(futures._PyFuture): # Inherit Python Task implementation
# from a Python Future implementation.
"""A coroutine wrapped in a Future."""
# An important invariant maintained while a Task not done:
# - Either _fut_waiter is None, and _step() is scheduled;
# - or _fut_waiter is some Future, and _step() is *not* scheduled.
# The only transition from the latter to the former is through
# _wakeup(). When _fut_waiter is not None, one of its callbacks
# If False, don't log a message if the task is destroyed whereas its
# status is still pending
_log_destroy_pending = True
def current_task(cls, loop=None):
"""Return the currently running task in an event loop or None.
By default the current task for the current event loop is returned.
None is returned when called not in the context of a Task.
warnings.warn("Task.current_task() is deprecated since Python 3.7, "
"use asyncio.current_task() instead",
loop = events.get_event_loop()
return current_task(loop)
def all_tasks(cls, loop=None):
"""Return a set of all tasks for an event loop.
By default all tasks for the current event loop are returned.
warnings.warn("Task.all_tasks() is deprecated since Python 3.7, "
"use asyncio.all_tasks() instead",
return _all_tasks_compat(loop)
def __init__(self, coro, *, loop=None, name=None):
super().__init__(loop=loop)
if self._source_traceback:
del self._source_traceback[-1]
if not coroutines.iscoroutine(coro):
# raise after Future.__init__(), attrs are required for __del__
# prevent logging for pending task in __del__
self._log_destroy_pending = False
raise TypeError(f"a coroutine was expected, got {coro!r}")
self._name = f'Task-{_task_name_counter()}'
self._must_cancel = False
self._context = contextvars.copy_context()
self._loop.call_soon(self.__step, context=self._context)
if self._state == futures._PENDING and self._log_destroy_pending:
'message': 'Task was destroyed but it is pending!',
if self._source_traceback:
context['source_traceback'] = self._source_traceback
self._loop.call_exception_handler(context)
return base_tasks._task_repr_info(self)
def set_name(self, value):
def set_result(self, result):
raise RuntimeError('Task does not support set_result operation')
def set_exception(self, exception):
raise RuntimeError('Task does not support set_exception operation')
def get_stack(self, *, limit=None):
"""Return the list of stack frames for this task's coroutine.
If the coroutine is not done, this returns the stack where it is
suspended. If the coroutine has completed successfully or was
cancelled, this returns an empty list. If the coroutine was
terminated by an exception, this returns the list of traceback
The frames are always ordered from oldest to newest.
The optional limit gives the maximum number of frames to
return; by default all available frames are returned. Its
meaning differs depending on whether a stack or a traceback is
returned: the newest frames of a stack are returned, but the
oldest frames of a traceback are returned. (This matches the
behavior of the traceback module.)
For reasons beyond our control, only one stack frame is
returned for a suspended coroutine.
return base_tasks._task_get_stack(self, limit)
def print_stack(self, *, limit=None, file=None):
"""Print the stack or traceback for this task's coroutine.
This produces output similar to that of the traceback module,
for the frames retrieved by get_stack(). The limit argument
is passed to get_stack(). The file argument is an I/O stream
to which the output is written; by default output is written
return base_tasks._task_print_stack(self, limit, file)
"""Request that this task cancel itself.
This arranges for a CancelledError to be thrown into the
wrapped coroutine on the next cycle through the event loop.
The coroutine then has a chance to clean up or even deny
the request using try/except/finally.
Unlike Future.cancel, this does not guarantee that the
task will be cancelled: the exception might be caught and
acted upon, delaying cancellation of the task or preventing
cancellation completely. The task may also return a value or
raise a different exception.
Immediately after this method is called, Task.cancelled() will
not return True (unless the task was already cancelled). A
task will be marked as cancelled when the wrapped coroutine
terminates with a CancelledError exception (even if cancel()
self._log_traceback = False
if self._fut_waiter is not None:
if self._fut_waiter.cancel():
# Leave self._fut_waiter; it may be a Task that
# catches and ignores the cancellation so we may have
# to cancel it again later.
# It must be the case that self.__step is already scheduled.
def __step(self, exc=None):
raise exceptions.InvalidStateError(
f'_step(): already done: {self!r}, {exc!r}')
if not isinstance(exc, exceptions.CancelledError):
exc = exceptions.CancelledError()
self._must_cancel = False
_enter_task(self._loop, self)
# Call either coro.throw(exc) or coro.send(None).
# We use the `send` method directly, because coroutines
# don't have `__iter__` and `__next__` methods.
except StopIteration as exc:
# Task is cancelled right before coro stops.
self._must_cancel = False
super().set_result(exc.value)
except exceptions.CancelledError:
super().cancel() # I.e., Future.cancel(self).
except (KeyboardInterrupt, SystemExit) as exc:
super().set_exception(exc)
except BaseException as exc:
super().set_exception(exc)
blocking = getattr(result, '_asyncio_future_blocking', None)
# Yielded Future must come from Future.__iter__().
if futures._get_loop(result) is not self._loop:
f'Task {self!r} got Future '
f'{result!r} attached to a different loop')
self.__step, new_exc, context=self._context)
f'Task cannot await on itself: {self!r}')
self.__step, new_exc, context=self._context)
result._asyncio_future_blocking = False
result.add_done_callback(
self.__wakeup, context=self._context)
self._fut_waiter = result
if self._fut_waiter.cancel():
self._must_cancel = False
f'yield was used instead of yield from '
f'in task {self!r} with {result!r}')
self.__step, new_exc, context=self._context)
# Bare yield relinquishes control for one event loop iteration.
self._loop.call_soon(self.__step, context=self._context)
elif inspect.isgenerator(result):
# Yielding a generator is just wrong.
f'yield was used instead of yield from for '
f'generator in task {self!r} with {result!r}')
self.__step, new_exc, context=self._context)
# Yielding something else is an error.
new_exc = RuntimeError(f'Task got bad yield: {result!r}')
self.__step, new_exc, context=self._context)
_leave_task(self._loop, self)
self = None # Needed to break cycles when an exception occurs.
def __wakeup(self, future):
except BaseException as exc:
# This may also be a cancellation.
# Don't pass the value of `future.result()` explicitly,
# as `Future.__iter__` and `Future.__await__` don't need it.
# If we call `_step(value, None)` instead of `_step()`,
# Python eval loop would use `.send(value)` method call,
# instead of `__next__()`, which is slower for futures
# that return non-generator iterators from their `__iter__`.
self = None # Needed to break cycles when an exception occurs.
# _CTask is needed for tests.
Task = _CTask = _asyncio.Task
def create_task(coro, *, name=None):
"""Schedule the execution of a coroutine object in a spawn task.
loop = events.get_running_loop()
task = loop.create_task(coro)
_set_task_name(task, name)
# wait() and as_completed() similar to those in PEP 3148.
FIRST_COMPLETED = concurrent.futures.FIRST_COMPLETED
FIRST_EXCEPTION = concurrent.futures.FIRST_EXCEPTION
ALL_COMPLETED = concurrent.futures.ALL_COMPLETED
async def wait(fs, *, loop=None, timeout=None, return_when=ALL_COMPLETED):
"""Wait for the Futures and coroutines given by fs to complete.
The fs iterable must not be empty.
Coroutines will be wrapped in Tasks.
Returns two sets of Future: (done, pending).
done, pending = await asyncio.wait(fs)
Note: This does not raise TimeoutError! Futures that aren't done
when the timeout occurs are returned in the second set.
if futures.isfuture(fs) or coroutines.iscoroutine(fs):
raise TypeError(f"expect a list of futures, not {type(fs).__name__}")
raise ValueError('Set of coroutines/Futures is empty.')
if return_when not in (FIRST_COMPLETED, FIRST_EXCEPTION, ALL_COMPLETED):
raise ValueError(f'Invalid return_when value: {return_when}')
loop = events.get_running_loop()
warnings.warn("The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning, stacklevel=2)
fs = {ensure_future(f, loop=loop) for f in set(fs)}
return await _wait(fs, timeout, return_when, loop)
def _release_waiter(waiter, *args):
async def wait_for(fut, timeout, *, loop=None):
"""Wait for the single Future or coroutine to complete, with timeout.
Coroutine will be wrapped in Task.
Returns result of the Future or coroutine. When a timeout occurs,
it cancels the task and raises TimeoutError. To avoid the task
cancellation, wrap it in shield().
If the wait is cancelled, the task is also cancelled.
This function is a coroutine.
loop = events.get_running_loop()
warnings.warn("The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning, stacklevel=2)
fut = ensure_future(fut, loop=loop)
await _cancel_and_wait(fut, loop=loop)
except exceptions.CancelledError as exc:
raise exceptions.TimeoutError() from exc
raise exceptions.TimeoutError()
waiter = loop.create_future()
timeout_handle = loop.call_later(timeout, _release_waiter, waiter)
cb = functools.partial(_release_waiter, waiter)
fut = ensure_future(fut, loop=loop)
fut.add_done_callback(cb)
# wait until the future completes or the timeout
except exceptions.CancelledError:
fut.remove_done_callback(cb)
# We must ensure that the task is not running
# after wait_for() returns.
# See https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
fut.remove_done_callback(cb)
# We must ensure that the task is not running
# after wait_for() returns.
# See https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
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