Exceptions support

[bschindler]

I am having an issue with this library in that an exception thrown in a coroutine can cause stalls. Here is a very simple sample code:

import asyncio
import nest_asyncio


async def nested_function():
   print("Nested function called")
   await asyncio.sleep(1)

async def crashing_function():
   print("Launching crashing function")
   await asyncio.sleep(0.01)
   raise RuntimeError("This thing crashed")

def recursive_function():
   print("Initial")
   loop = asyncio.get_running_loop()
   loop.run_until_complete(nested_function())

async def calls_recursive():
   await asyncio.sleep(0.01)
   recursive_function()

async def async_main():
   print("Async main")
   nest_asyncio.apply(loop)
   tasks = [calls_recursive(), crashing_function()]
   print("Async main resuming")
   await asyncio.gather(*tasks)

loop = asyncio.get_event_loop()
loop.run_until_complete(async_main())

What I would expect this code to do is that the nested run_until_complete to finish the nested function and that the excpetion thrown in crashing_function() to be report in the await asyncio.gather() call. Instead, the nested run_until_complete call just hangs forever

[erdewit]

If the nest_asyncio.apply() is moved to the top (after the imports) it will work. Otherwise there's an unpatched task that causes problems.