164 lines
4.1 KiB
Python
164 lines
4.1 KiB
Python
from __future__ import annotations
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import enum
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from dataclasses import dataclass
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from typing import Any, Generic, Literal, TypeVar, overload
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from weakref import WeakKeyDictionary
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from ._core._eventloop import get_async_backend
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T = TypeVar("T")
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D = TypeVar("D")
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async def checkpoint() -> None:
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"""
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Check for cancellation and allow the scheduler to switch to another task.
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Equivalent to (but more efficient than)::
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await checkpoint_if_cancelled()
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await cancel_shielded_checkpoint()
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.. versionadded:: 3.0
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"""
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await get_async_backend().checkpoint()
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async def checkpoint_if_cancelled() -> None:
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"""
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Enter a checkpoint if the enclosing cancel scope has been cancelled.
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This does not allow the scheduler to switch to a different task.
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.. versionadded:: 3.0
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"""
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await get_async_backend().checkpoint_if_cancelled()
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async def cancel_shielded_checkpoint() -> None:
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"""
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Allow the scheduler to switch to another task but without checking for cancellation.
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Equivalent to (but potentially more efficient than)::
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with CancelScope(shield=True):
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await checkpoint()
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.. versionadded:: 3.0
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"""
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await get_async_backend().cancel_shielded_checkpoint()
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def current_token() -> object:
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"""
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Return a backend specific token object that can be used to get back to the event
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loop.
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"""
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return get_async_backend().current_token()
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_run_vars: WeakKeyDictionary[Any, dict[str, Any]] = WeakKeyDictionary()
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_token_wrappers: dict[Any, _TokenWrapper] = {}
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@dataclass(frozen=True)
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class _TokenWrapper:
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__slots__ = "_token", "__weakref__"
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_token: object
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class _NoValueSet(enum.Enum):
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NO_VALUE_SET = enum.auto()
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class RunvarToken(Generic[T]):
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__slots__ = "_var", "_value", "_redeemed"
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def __init__(self, var: RunVar[T], value: T | Literal[_NoValueSet.NO_VALUE_SET]):
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self._var = var
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self._value: T | Literal[_NoValueSet.NO_VALUE_SET] = value
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self._redeemed = False
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class RunVar(Generic[T]):
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"""
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Like a :class:`~contextvars.ContextVar`, except scoped to the running event loop.
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"""
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__slots__ = "_name", "_default"
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NO_VALUE_SET: Literal[_NoValueSet.NO_VALUE_SET] = _NoValueSet.NO_VALUE_SET
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_token_wrappers: set[_TokenWrapper] = set()
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def __init__(
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self, name: str, default: T | Literal[_NoValueSet.NO_VALUE_SET] = NO_VALUE_SET
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):
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self._name = name
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self._default = default
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@property
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def _current_vars(self) -> dict[str, T]:
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token = current_token()
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try:
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return _run_vars[token]
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except KeyError:
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run_vars = _run_vars[token] = {}
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return run_vars
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@overload
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def get(self, default: D) -> T | D:
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...
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@overload
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def get(self) -> T:
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...
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def get(
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self, default: D | Literal[_NoValueSet.NO_VALUE_SET] = NO_VALUE_SET
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) -> T | D:
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try:
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return self._current_vars[self._name]
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except KeyError:
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if default is not RunVar.NO_VALUE_SET:
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return default
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elif self._default is not RunVar.NO_VALUE_SET:
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return self._default
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raise LookupError(
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f'Run variable "{self._name}" has no value and no default set'
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)
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def set(self, value: T) -> RunvarToken[T]:
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current_vars = self._current_vars
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token = RunvarToken(self, current_vars.get(self._name, RunVar.NO_VALUE_SET))
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current_vars[self._name] = value
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return token
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def reset(self, token: RunvarToken[T]) -> None:
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if token._var is not self:
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raise ValueError("This token does not belong to this RunVar")
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if token._redeemed:
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raise ValueError("This token has already been used")
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if token._value is _NoValueSet.NO_VALUE_SET:
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try:
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del self._current_vars[self._name]
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except KeyError:
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pass
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else:
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self._current_vars[self._name] = token._value
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token._redeemed = True
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def __repr__(self) -> str:
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return f"<RunVar name={self._name!r}>"
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