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# Copyright (c) 2022 Tulir Asokan
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
from __future__ import annotations
from typing import Any
import functools
from mautrix import __optional_imports__
if __optional_imports__:
from typing import Awaitable, Callable, ParamSpec
Param = ParamSpec("Param")
Func = Callable[Param, Awaitable[Any]]
def async_getter_lock(fn: Func) -> Func:
"""
A utility decorator for locking async getters that have caches
(preventing race conditions between cache check and e.g. async database actions).
The class must have an ```_async_get_locks`` defaultdict that contains :class:`asyncio.Lock`s
(see example for exact definition). Non-cache-affecting arguments should be only passed as
keyword args.
Args:
fn: The function to decorate.
Returns:
The decorated function.
Examples:
>>> import asyncio
>>> from collections import defaultdict
>>> class User:
... _async_get_locks: dict[Any, asyncio.Lock] = defaultdict(lambda: asyncio.Lock())
... db: Any
... cache: dict[str, User]
... @classmethod
... @async_getter_lock
... async def get(cls, id: str, *, create: bool = False) -> User | None:
... try:
... return cls.cache[id]
... except KeyError:
... pass
... user = await cls.db.fetch_user(id)
... if user:
... return user
... elif create:
... return await cls.db.create_user(id)
... return None
"""
@functools.wraps(fn)
async def wrapper(cls, *args, **kwargs) -> Any:
async with cls._async_get_locks[args]:
return await fn(cls, *args, **kwargs)
return wrapper
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