Use the recommended async with syntax to acquire and release an asyncio Lock.

See https://docs.python.org/3/library/asyncio-sync.html#asyncio.Lock

I think this also works in Python 3.5: https://docs.python.org/3/whatsnew/3.5.html#pep-492-coroutines-with-async-and-await-syntax

Author: jasongrout

jupyter_server_proxy/handlers.py

@@ -491,7 +491,7 @@ async def ensure_process(self):
         # FIXME: Make sure this times out properly?
         # Invariant here should be: when lock isn't being held, either 'proc' is in state &
         # running, or not.
-        with (await self.state['proc_lock']):
+        async with self.state['proc_lock']:
             if 'proc' not in self.state:
                 # FIXME: Prevent races here
                 # FIXME: Handle graceful exits of spawned processes here