[SOLVED] `eventlet.spawn` doesn't work as expected

`eventlet.spawn` doesn't work as expected

I'm writing a web UI for data analysis tasks.

Here's the way it's supposed to work:

After a user specifies parameters like dataset and learning rate, I create a new task record, then a executor for this task is started asyncly (The executor may take a long time to run.), and the user is redirected to some other page.

After searching for an async library for python, I started with eventlet, here's what I wrote in a flask view function:

db.save(task)
eventlet.spawn(executor, task)
return redirect("/show_tasks")

With the code above, the executor didn't execute at all.

What may be the problem of my code? Or maybe I should try something else?

Solution

You'll need to patch some system libraries in order to make eventlet work. Here is a minimal working example (also as gist):

#!/usr/bin/env python 

from flask import Flask 
import time 
import eventlet 

eventlet.monkey_patch() 

app = Flask(__name__) 
app.debug = True 

def background(): 
    """ do something in the background """ 
    print('[background] working in the background...') 
    time.sleep(2) 
    print('[background] done.') 
    return 42 

def callback(gt, *args, **kwargs): 
    """ this function is called when results are available """ 
    result = gt.wait() 
    print("[cb] %s" % result) 

@app.route('/') 
def index(): 
    greenth = eventlet.spawn(background) 
    greenth.link(callback) 
    return "Hello World" 

if __name__ == '__main__': 
    app.run()