title: Can gevent workers be used in the python 3 app engine standard environment?
body: <p>Attempting to use them gives me the following error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/env/lib/python3.7/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
      worker.init_process()
    File "/env/lib/python3.7/site-packages/gunicorn/workers/ggevent.py", line 196, in init_process
      self.patch()
    File "/env/lib/python3.7/site-packages/gunicorn/workers/ggevent.py", line 75, in patch
      fileno=s.sock.fileno()))
    File "/env/lib/python3.7/site-packages/gevent/_socket3.py", line 114, in __init__
      self._sock = self._gevent_sock_class(family, type, proto, fileno)
  OSError: [Errno 92] Protocol not available: 'protocol'
  </code></pre>
  
  <p>Are sockets not supported in the python 3 environment? Is this the reason it won't work?</p>
  
  <p>My application spends a lot of time blocked on other web servers, so using async workers is necessary for decent performance. In the meantime I will try using <code>eventlet</code> workers instead.</p>
  
  <p>EDIT: Including some more context around usage</p>
  
  <p>app.yaml</p>
  
  <pre><code>runtime: python37
  instance_class: F2
  
  entrypoint: gunicorn -c gunicorn.conf.py -b :$PORT my_project.server:app
  </code></pre>
  
  <p>gunicorn.conf.py</p>
  
  <pre><code># Recommended number of workers based on instance size:
  # https://cloud.google.com/appengine/docs/standard/python3/runtime#entrypoint_best_practices
  workers = 2
  # Use an asynchronous worker as most of the work is waiting for websites to load
  worker_class = 'gevent'
  </code></pre>
  
  <p>Since it is during gunicorn launch I don't believe the app definition context will be useful. However for completeness I'm launching a basic flask application. Something like:</p>
  
  <p>my_project/server.py</p>
  
  <pre><code>from flask import Flask
  
  from my_project.handlers import run
  
  app = Flask(__name__)
  app.register_blueprint(run, url_prefix='/run')
  </code></pre>