Client close if loop is still running (#760)

Author: martindurant

s3fs/core.py

@@ -541,6 +541,12 @@ async def set_session(self, refresh=False, kwargs={}):
     @staticmethod
     def close_session(loop, s3):
         if loop is not None and loop.is_running():
+            try:
+                loop = asyncio.get_event_loop()
+                loop.create_task(s3.__aexit__(None, None, None))
+                return
+            except RuntimeError:
+                pass
             try:
                 sync(loop, s3.__aexit__, None, None, None, timeout=0.1)
                 return