对 coroutine.__await__() 调用 next 为什么会导致重复进入 Future.__await__()

import types
from typing import Any, Awaitable


@types.coroutine
def _async_yield(obj):
    return (yield obj)


async def gather(*aws: Awaitable[Any], return_exceptions: bool = False):
    result_array: list[Any] = [None for _ in range(len(aws))]
    done, pending = [], [*aws]
    while pending:
        for i, awaitable in enumerate(aws):
            if awaitable in done:
                continue
            try:
                next(awaitable.__await__())
                await _async_yield(None)
            except StopIteration as exc:
                result_array[i] = exc.value
                done.append(awaitable)
                pending.remove(awaitable)
            except BaseException as exc:
                if not return_exceptions:
                    raise
                result_array[i] = exc
                done.append(awaitable)
                pending.remove(awaitable)
    return result_array


async def test_wait():
    async def a():
        return 1

    async def b():
        import asyncio

        await asyncio.sleep(0)
        return 2

    async def c():
        import asyncio

        await asyncio.sleep(1)
        return 3

    return await gather(a(), b(), c(), asyncio.create_task(c()))


if __name__ == "__main__":
    import asyncio

    print(asyncio.run(test_wait()))

报错所处的位置：

    # asyncio/futures.py line 281
    def __await__(self):
        if not self.done():
            self._asyncio_future_blocking = True
            yield self  # This tells Task to wait for completion.
        if not self.done():
            raise RuntimeError("await wasn't used with future")
        return self.result()  # May raise too.