Regarding the example _get_loop():

```
       def _get_loop(self):
           loop = asyncio.get_running_loop()
           if self._loop is None:
                self._loop = loop
           if loop is not self._loop: raise
           if not loop.is_running(): raise
```

Would this be added to all asyncio primitives to be called anytime a reference to the loop is needed within a coroutine?

Also, regarding the last line "if not loop.is_running(): raise" I'm not 100% certain that I understand the purpose. Wouldn't it already raise a RuntimeError from `asyncio.get_running_loop()` if the event loop wasn't running?

The only thing I can think of where it would have an effect is if somehow the event loop was running at the start of `_get_loop()` and then the event loop was stopped (e.g. a loop in an alternative thread was stopped by the main thread while the alternative thread was in the middle of executing `_get_loop()`). But to me, that seems to be enough of an edge case to simplify it to the following:


```
       def _get_loop(self):
           loop = asyncio.get_running_loop()
           if self._loop is None:
                self._loop = loop
           if loop is not self._loop: raise
```

(Unless you intended for the first line `loop = asyncio.get_running_loop()` to instead be using the private `asyncio._get_running_loop()`, which returns None and doesn't raise. In that case, the original would be good to me.)

Other than that, I think the approach seems solid.