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from __future__ import annotations
import math
from collections.abc import Generator
from contextlib import contextmanager
from types import TracebackType
from ..abc._tasks import TaskGroup, TaskStatus
from ._eventloop import get_async_backend
class _IgnoredTaskStatus(TaskStatus[object]):
def started(self, value: object = None) -> None:
pass
TASK_STATUS_IGNORED = _IgnoredTaskStatus()
class CancelScope:
"""
Wraps a unit of work that can be made separately cancellable.
:param deadline: The time (clock value) when this scope is cancelled automatically
:param shield: ``True`` to shield the cancel scope from external cancellation
"""
def __new__(
cls, *, deadline: float = math.inf, shield: bool = False
) -> CancelScope:
return get_async_backend().create_cancel_scope(shield=shield, deadline=deadline)
def cancel(self) -> None:
"""Cancel this scope immediately."""
raise NotImplementedError
@property
def deadline(self) -> float:
"""
The time (clock value) when this scope is cancelled automatically.
Will be ``float('inf')`` if no timeout has been set.
"""
raise NotImplementedError
@deadline.setter
def deadline(self, value: float) -> None:
raise NotImplementedError
@property
def cancel_called(self) -> bool:
"""``True`` if :meth:`cancel` has been called."""
raise NotImplementedError
@property
def cancelled_caught(self) -> bool:
"""
``True`` if this scope suppressed a cancellation exception it itself raised.
This is typically used to check if any work was interrupted, or to see if the
scope was cancelled due to its deadline being reached. The value will, however,
only be ``True`` if the cancellation was triggered by the scope itself (and not
an outer scope).
"""
raise NotImplementedError
@property
def shield(self) -> bool:
"""
``True`` if this scope is shielded from external cancellation.
While a scope is shielded, it will not receive cancellations from outside.
"""
raise NotImplementedError
@shield.setter
def shield(self, value: bool) -> None:
raise NotImplementedError
def __enter__(self) -> CancelScope:
raise NotImplementedError
def __exit__(
self,
exc_type: type[BaseException] | None,
exc_val: BaseException | None,
exc_tb: TracebackType | None,
) -> bool | None:
raise NotImplementedError
@contextmanager
def fail_after(
delay: float | None, shield: bool = False
) -> Generator[CancelScope, None, None]:
"""
Create a context manager which raises a :class:`TimeoutError` if does not finish in
time.
:param delay: maximum allowed time (in seconds) before raising the exception, or
``None`` to disable the timeout
:param shield: ``True`` to shield the cancel scope from external cancellation
:return: a context manager that yields a cancel scope
:rtype: :class:`~typing.ContextManager`\\[:class:`~anyio.CancelScope`\\]
"""
current_time = get_async_backend().current_time
deadline = (current_time() + delay) if delay is not None else math.inf
with get_async_backend().create_cancel_scope(
deadline=deadline, shield=shield
) as cancel_scope:
yield cancel_scope
if cancel_scope.cancelled_caught and current_time() >= cancel_scope.deadline:
raise TimeoutError
def move_on_after(delay: float | None, shield: bool = False) -> CancelScope:
"""
Create a cancel scope with a deadline that expires after the given delay.
:param delay: maximum allowed time (in seconds) before exiting the context block, or
``None`` to disable the timeout
:param shield: ``True`` to shield the cancel scope from external cancellation
:return: a cancel scope
"""
deadline = (
(get_async_backend().current_time() + delay) if delay is not None else math.inf
)
return get_async_backend().create_cancel_scope(deadline=deadline, shield=shield)
def current_effective_deadline() -> float:
"""
Return the nearest deadline among all the cancel scopes effective for the current
task.
:return: a clock value from the event loop's internal clock (or ``float('inf')`` if
there is no deadline in effect, or ``float('-inf')`` if the current scope has
been cancelled)
:rtype: float
"""
return get_async_backend().current_effective_deadline()
def create_task_group() -> TaskGroup:
"""
Create a task group.
:return: a task group
"""
return get_async_backend().create_task_group()
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