[jira] [Created] (TINKERPOP-2759) gremlinpython gives error "RuntimeError: Cannot run the event loop while another loop is running".

["Gavin Aten (Jira)" <ji...@apache.org>]

Gavin Aten created TINKERPOP-2759:
-------------------------------------

             Summary: gremlinpython gives error "RuntimeError: Cannot run the event loop while another loop is running".
                 Key: TINKERPOP-2759
                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2759
             Project: TinkerPop
          Issue Type: Bug
          Components: python
    Affects Versions: 3.6.0
         Environment: I am running the code inside Docker with Python 3.9 on Ubuntu 20.04 with relevant package versions as follows:

gremlinpython==3.6.0
uvicorn==0.17.6
fastapi==0.78.0


            Reporter: Gavin Aten
             Fix For: 3.6.0


Im not sure if this is the correct place to post an issue. If not, I can redirect this elsewhere.



I am trying to run a fastapi app with uvicorn but am struggling to run a gremlinpython query inside. It seems like gremlinpython tries to start up a new event loop while one is already running. Is it possible to get gremlinpython to use the current event loop if there is one running?

The following code snippet works when running with python3 but fails when running with uvicorn




```

from gremlin_python.structure.graph import Graph
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection


from fastapi import FastAPI


def run_query(conn_string, vertex_id):
graph= Graph()
remoteConn= DriverRemoteConnection(conn_string, 'g')
g=graph.traversal().withRemote(remoteConn)


details=g.V(vertex_id).valueMap(True).toList()
print(details)


remoteConn.close()
return FastAPI()


conn_string = '<conn_string>'
vertex_id = <'vertex_id'>


app = run_query(conn_string, vertex_id)


# running with: 
# uvicorn \{file_name}:app
# python3 \{file_name}

```

The error when running with uvicorn is as follows:

```

File "/code/./app/main2.py", line 20, in <module>
    app = run_query(conn_string, vertex_id)
  File "/code/./app/main2.py", line 11, in run_query
    details = g.V(vertex_id).valueMap(True).toList()
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/process/traversal.py", line 62, in toList
    return self.to_list()
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/process/traversal.py", line 65, in to_list
    return list(iter(self))
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/process/traversal.py", line 48, in __next__
    self.traversal_strategies.apply_strategies(self)
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/process/traversal.py", line 682, in apply_strategies
    traversal_strategy.apply(traversal)
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/remote_connection.py", line 78, in apply
    remote_traversal = self.remote_connection.submit(traversal.bytecode)
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/driver_remote_connection.py", line 102, in submit
    result_set = self._client.submit(bytecode, request_options=self._extract_request_options(bytecode))
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/client.py", line 148, in submit
    return self.submit_async(message, bindings=bindings, request_options=request_options).result()
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/client.py", line 180, in submit_async
    return conn.write(message)
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/connection.py", line 55, in write
    self.connect()
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/connection.py", line 45, in connect
    self._transport.connect(self._url, self._headers)
  File "/usr/local/lib/python3.9/dist-packages/gremlin_python/driver/aiohttp/transport.py", line 80, in connect
    self._loop.run_until_complete(async_connect())
  File "uvloop/loop.pyx", line 1495, in uvloop.loop.Loop.run_until_complete
  File "uvloop/loop.pyx", line 1488, in uvloop.loop.Loop.run_until_complete
  File "uvloop/loop.pyx", line 1377, in uvloop.loop.Loop.run_forever
  File "uvloop/loop.pyx", line 515, in uvloop.loop.Loop._run
RuntimeError: Cannot run the event loop while another loop is running

```



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