to_thread.py

"""
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/>
"""
from __future__ import annotations

import asyncio
import threading
from typing import (
    Any,
    Awaitable,
    Callable,
    Coroutine,
    Generator,
    Optional,
    TypeVar,
    Union,
)
from typing_extensions import T_Params, T_Return

T = TypeVar("T")


def to_thread(coro: Union[Generator[Any, None, T], Awaitable[T]]) -> T:

    result: Optional[T] = None
    exception: Optional[BaseException] = None
    event_loop = asyncio.get_event_loop_policy().new_event_loop()

    def target() -> None:
        nonlocal result
        nonlocal exception
        asyncio.set_event_loop(event_loop)
        try:
            result = asyncio.get_event_loop().run_until_complete(coro)
        except BaseException as err:
            exception = err
        asyncio.get_event_loop().stop()

    thread = threading.Thread(target=target)
    thread.start()
    thread.join()
    if result:
        return result
    elif exception:
        raise exception
    else:
        raise Exception("Unexpected error occured")


def run_in_thread(
    func: Callable[T_Params, Coroutine[None, None, T_Return]]
) -> Callable[T_Params, T_Return]:
    """Make a coroutine function into a function which runs in its own thread.

    Be careful when using this function, because the coroutine runs within a thread with its own event loop.
    It's not possible to await coroutines or futures created in an event loop from another
    """

    def wrapper(*args: T_Params.args, **kwargs: T_Params.kwargs) -> T_Return:
        return to_thread(func(*args, **kwargs))

    return wrapper