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

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 3.6.0
• Component/s: python
• 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
• Assignee: Unassigned
• Reporter: Gavin Aten
• Created: 19/Jun/22 17:40
• Updated: 20/Jun/22 18:47
• Resolved: 20/Jun/22 18:47

Description

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 (run over AWS Neptune DB) 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

 

 

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

 

Issue Links

• duplicates: TINKERPOP-2755 gremlinpython gives error "RuntimeError: Cannot run the event loop while another loop is running".