Everything here depends on a volume of the website. CherryPy is a threaded server and once every thread is waiting for database, new requests won't be processed. There's also aspect of request queue, but in general it is so.
Poor man's solution
If you know that you have small traffic you can try to workaround. Increase response.timeout if needed (default is 300 seconds). Increase server.thread_pool (defaults to 10). If you use reserve proxy, like nginx, in front of CherryPy application, increase proxy timeout there as well.
The following solutions will require you to redesign your website. Specifically to make it asynchronous, where client code sends a task, and then uses pull or push to get its result. It will require changes on both sides of the wire.
CherryPy BackgroundTask
You can make use of cherrypy.process.plugins.BackgroundTask and some intermediary storage (e.g. new table in your database) at server side. XmlHttpRequest for pull or WebSockets for push to client side. CherryPy can handle both.
Note that because CherryPy is run in single Python process, the background task's thread will run within it too. If you do some SQL result set post-processing, you will be affected by GIL. So you may want rewrite it to use processes instead, which is a little more complicated.
Industrial solution
If your website operates or is deemed to operate at scale, you are better to consider a distributed task queue like Rq or Celery. It makes server-side difference. Client side is the same pull or push.
Example
Here follows a toy implementation for BackgroundTags with XHR polling.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import time
import uuid
import cherrypy
from cherrypy.process.plugins import BackgroundTask
config = {
'global' : {
'server.socket_host' : '127.0.0.1',
'server.socket_port' : 8080,
'server.thread_pool' : 8,
}
}
class App:
_taskResultMap = None
def __init__(self):
self._taskResultMap = {}
def _target(self, task, id, arg):
time.sleep(10) # long one, right?
try:
self._taskResultMap[id] = 42 + arg
finally:
task.cancel()
@cherrypy.expose
@cherrypy.tools.json_out()
def schedule(self, arg):
id = str(uuid.uuid1())
self._taskResultMap[id] = None
task = BackgroundTask(
interval = 0, function = self._target, args = [id, int(arg)],
bus = cherrypy.engine)
task.args.insert(0, task)
task.start()
return str(id)
@cherrypy.expose
@cherrypy.tools.json_out()
def poll(self, id):
if self._taskResultMap[id] is None:
return {'id': id, 'status': 'wait', 'result': None}
else:
return {
'id' : id,
'status' : 'ready',
'result' : self._taskResultMap.pop(id)
}
@cherrypy.expose
def index(self):
return '''<!DOCTYPE html>
<html>
<head>
<title>CherryPy BackgroundTask demo</title>
<script type='text/javascript'
src='http://cdnjs.cloudflare.com/ajax/libs/qooxdoo/3.5.1/q.min.js'>
</script>
<script type='text/javascript'>
// Do not structure you real JavaScript application this way.
// This callback spaghetti is only for brevity.
function sendSchedule(arg, callback)
{
var xhr = q.io.xhr('/schedule?arg=' + arg);
xhr.on('loadend', function(xhr)
{
if(xhr.status == 200)
{
callback(JSON.parse(xhr.responseText))
}
});
xhr.send();
};
function sendPoll(id, callback)
{
var xhr = q.io.xhr('/poll?id=' + id);
xhr.on('loadend', function(xhr)
{
if(xhr.status == 200)
{
callback(JSON.parse(xhr.responseText))
}
});
xhr.send();
}
function start(event)
{
event.preventDefault();
// example argument to pass to the task
var arg = Math.round(Math.random() * 100);
sendSchedule(arg, function(id)
{
console.log('scheduled (', arg, ') as', id);
q.create('<li/>')
.setAttribute('id', id)
.append('<span>' + id + ': 42 + ' + arg +
' = <img src="http://sstatic.net/Img/progress-dots.gif" />' +
'</span>')
.appendTo('#result-list');
var poll = function()
{
console.log('polling', id);
sendPoll(id, function(response)
{
console.log('polled', id, '(', response, ')');
if(response.status == 'wait')
{
setTimeout(poll, 2500);
}
else if(response.status == 'ready')
{
q('#' + id)
.empty()
.append('<span>' + id + ': 42 + ' + arg + ' = ' +
response.result + '</span>');
}
});
};
setTimeout(poll, 2500);
});
}
q.ready(function()
{
q('#run').on('click', start);
});
</script>
</head>
<body>
<p>
<a href='#' id='run'>Run a long task</a>, look in browser console.
</p>
<ul id='result-list'></ul>
</body>
</html>
'''
if __name__ == '__main__':
cherrypy.quickstart(App(), '/', config)
