My code (Python 3.5 on Raspbian 9 - Stretch) is divided up into a number of separate processes, which are run from main.py. A simplified example of my code is below, which I believe is plain vanilla use of Flask, socketIO, eventlet with multiprocessing.Process. The problem is it hangs when I try to access the pipe that connects the different processes.
My understanding (which wouldn’t surprise me if I was completely wrong) is that this is a long standing issue related to eventlet and multiprocessing.Process and as of January 2018 has not been resolved. How to combine multiprocessing and eventlet https://github.com/eventlet/eventlet/issues/147
My question is this. This seems like a common use case, but doesn’t work. So, what work around or different approach would you recommend?
--- in webprocess.py ---
#!/usr/bin/python3
def WebFunc(outfrompipe, intopipe):
global thread
app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app, async_mode=”eventlet”)
thread = None
thread_lock = Lock()
@app.route('/')
def index():
return render_template('index.html', async_mode=socketio.async_mode)
@socketio.on('my_event', namespace='/test')
def test_msg(msg):
# Receive a message from a web app
print(“Received message”, msg)
# Send this message to another process
# THIS IS WHERE IT HANGS!!
intopipe.send(msg)
socketio.run(app, debug=False, host='0.0.0.0')
--- in main.py ---
#!/usr/bin/python3
import webprocess as webproc
import multiprocessing
import time
if __name__ == '__main__':
multiprocessing.set_start_method('spawn')
outfrompipe, intopipe = multiprocessing.Pipe()
wf = multiprocessing.Process(name=”WebProc”, target=webproc.WebFunc,
args=(outfrompipe, intopipe))
wf.start()
while True:
message = outfrompipe.recv()
print(message)
time.sleep(1)
wf.join()
