Python Asyncio中Coroutines,Tasks,Future可等待对象的关系及作用

import asyncio
async def main():
    await asyncio.sleep(0)
asyncio.run(main())

class Runner:
    ...
    def run(self, coro, *, context=None):
        """Run a coroutine inside the embedded event loop."""
        # 省略代码
        ...

        # 把coroutine转为task
        task = self._loop.create_task(coro, context=context)

        # 省略代码
        ...

        try:
            # 如果传入的是Future或者coroutine，也会专为task
            return self._loop.run_until_complete(task)
        except exceptions.CancelledError:

        # 省略代码
        ...

import asyncio
async def main():
    await asyncio.create_task(asyncio.sleep(0))
asyncio.run(main())

# demo_coro.py
import asyncio
import time
async def main():
    await asyncio.sleep(1)
    await asyncio.sleep(2)
s_t = time.time()
asyncio.run(main())
print(time.time() - s_t)
# // Output: 3.0028765201568604
# demo_task.py
import asyncio
import time
async def main():
    task_1 = asyncio.create_task(asyncio.sleep(1))
    task_2 = asyncio.create_task(asyncio.sleep(2))
    await task_1
    await task_2

s_t = time.time()
asyncio.run(main())
print(time.time() - s_t)
# // Output: 2.0027475357055664

class Future:
    ...
    def set_result(self, result):
        """设置结果，并安排下一个调用"""
        if self._state != _PENDING:
            raise exceptions.InvalidStateError(f'{self._state}: {self!r}')
        self._result = result
        self._state = _FINISHED
        self.__schedule_callbacks()
    def set_exception(self, exception):
        """设置异常，并安排下一个调用"""
        if self._state != _PENDING:
            raise exceptions.InvalidStateError(f'{self._state}: {self!r}')
        if isinstance(exception, type):
            exception = exception()
        if type(exception) is StopIteration:
            raise TypeError("StopIteration interacts badly with generators "
                            "and cannot be raised into a Future")
        self._exception = exception
        self._state = _FINISHED
        self.__schedule_callbacks()
        self.__log_traceback = True
    def __await__(self):
        """设置为blocking，并接受await或者yield from调用"""
        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.

    __iter__ = __await__  # make compatible with 'yield from'.

async def demo(future: asyncio.Future):
    await future
    print("aha")

class Task(futures._PyFuture):  # Inherit Python Task implementation                            # from a Python Future implementation.
    _log_destroy_pending = True
    def __init__(self, coro, *, loop=None, name=None, context=None):
        super().__init__(loop=loop)
        # 省略部分初始化代码
        ...
        # 托管的coroutine
        self._coro = coro
        if context is None:
            self._context = contextvars.copy_context()
        else:
            self._context = context
        # 通过loop.call_sonn，在Task初始化后马上就通知事件循环在下次有空的时候执行自己的__step函数
        self._loop.call_soon(self.__step, context=self._context)
    def __step(self, exc=None):
        coro = self._coro
        # 方便asyncio自省
        _enter_task(self._loop, self)
        # Call either coro.throw(exc) or coro.send(None).
        try:
            if exc is None:
                # 通过send预激托管的coroutine
                # 这时候只会得到coroutine yield回来的数据或者收到一个StopIteration的异常
                # 对于Future或者Task返回的是Self
                result = coro.send(None)
            else:
                # 发送异常给coroutine 
                result = coro.throw(exc)
        except StopIteration as exc:
            # StopIteration代表Coroutine运行完毕
            if self._must_cancel:
                # coroutine在停止之前被执行了取消操作，则需要显示的执行取消操作
                self._must_cancel = False
                super().cancel(msg=self._cancel_message)
            else:
                # 把运行完毕的值发送到结果值中
                super().set_result(exc.value)
        # 省略其它异常封装
        ...
        else:
            # 如果没有异常抛出
            blocking = getattr(result, '_asyncio_future_blocking', None)
            if blocking is not None:
                # 通过Future代码可以判断，如果带有_asyncio_future_blocking属性，则代表当前result是Future或者是Task
                # 意味着这个Task里面裹着另外一个的Future或者Task
                # 省略Future判断
                ...

                if blocking:
                    # 代表这这个Future或者Task处于卡住的状态，
                    # 此时的Task放弃了自己对事件循环的控制权，等待这个卡住的Future或者Task执行完成时唤醒一下自己
                    result._asyncio_future_blocking = False
                    result.add_done_callback(self.__wakeup, context=self._context)
                    self._fut_waiter = result
                    if self._must_cancel:
                        if self._fut_waiter.cancel(msg=self._cancel_message):
                            self._must_cancel = False
                else:
                    # 不能被await两次
                    new_exc = RuntimeError(
                        f'yield was used instead of yield from '
                        f'in task {self!r} with {result!r}')
                    self._loop.call_soon(
                        self.__step, new_exc, context=self._context)

            elif result is None:
                # 放弃了对事件循环的控制权，代表自己托管的coroutine可能有个coroutine在运行，接下来会把控制权交给他和事件循环 
                # 当前的coroutine里面即使没有Future或者Task,但是子Future可能有
                self._loop.call_soon(self.__step, context=self._context)
        finally:
            _leave_task(self._loop, self)
            self = None  # Needed to break cycles when an exception occurs.

    def __wakeup(self, future):
        # 其它Task和Future完成后会调用到该函数，接下来进行一些处理
        try:
            # 回收Future的状态，如果Future发生了异常，则把异常传回给自己
            future.result()
        except BaseException as exc:
            # This may also be a cancellation.
            self.__step(exc)
        else:
            # Task并不需要自己托管的Future的结果值，而且如下注释，这样能使调度变得更快
            # Don't pass the value of `future.result()` explicitly,
            # as `Future.__iter__` and `Future.__await__` don't need it.
            # If we call `_step(value, None)` instead of `_step()`,
            # Python eval loop would use `.send(value)` method call,
            # instead of `__next__()`, which is slower for futures
            # that return non-generator iterators from their `__iter__`.
            self.__step()
        self = None  # Needed to break cycles when an exception occurs.

# demo_coro.py
import asyncio
import time
async def main():
    await asyncio.sleep(1)
    await asyncio.sleep(2)
s_t = time.time()
asyncio.run(main())
print(time.time() - s_t)
# // Output: 3.0028765201568604

# demo_task.py
import asyncio
import time
async def main():
    task_1 = asyncio.create_task(asyncio.sleep(1))
    task_2 = asyncio.create_task(asyncio.sleep(2))
    await task_1
    await task_2
s_t = time.time()
asyncio.run(main())
print(time.time() - s_t)
# // Output: 2.0027475357055664

# demo_task.py
import asyncio
import time
def mutli_task():
    task_1 = asyncio.create_task(asyncio.sleep(1))
    task_2 = asyncio.create_task(asyncio.sleep(2))
async def main():
    mutli_task()
    await asyncio.sleep(1.5) 
s_t = time.time()
asyncio.run(main())
print(time.time() - s_t)
# // Output: 1.5027475357055664