与 asyncio.to_thread 相反

Question

如何以阻塞方式运行异步函数？我不允许修改我的模拟函数 f1() 的签名，也不能轻易切换到 async def，因此不能使用 await 表达式。

async def cc2():
    await asyncio.sleep(1)
    await asyncio.to_thread(print, "qwerty")

def f1():
    t = asyncio.create_task(cc2())
    # wait until the task finished before returning

async def main():
    f1()  # typical call from many places of a program

asyncio.run(main())

我尝试了asyncio.get_running_loop().run_until_complete(t)，但破解不起作用，我收到下一个错误。

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.9/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "<stdin>", line 2, in main
  File "<stdin>", line 3, in f1
  File "/usr/lib/python3.9/asyncio/base_events.py", line 618, in run_until_complete
    self._check_running()
  File "/usr/lib/python3.9/asyncio/base_events.py", line 578, in _check_running
    raise RuntimeError('This event loop is already running')
RuntimeError: This event loop is already running

Answer 1

如何以阻塞方式运行异步函数？

如果您在同步代码中，您可以使用asyncio.run(async_function()) 调用它。如果你在异步代码中，你可以await async_function() 或asyncio.create_task(async_function())，后者安排它在后台运行。不允许在异步代码中使用 asyncio.run()（或 run_until_complete，即使是新创建的事件循环对象），因为它会阻塞并可能停止外部事件循环。

但如果您需要它来进行测试，您可以随时执行以下操作：

# XXX dangerous - could block the current event loop
with concurrent.futures.ThreadPoolExecutor() as pool:
    pool.submit(asyncio.run, async_function()).result()