ASync Shell Commands from Tornado

I’ve been using Tornado at work for a bunch of web interface stuff and found I needed to call shell commands that might block for a while.  To avoid blocking Tornado itself, I looked around the web for a while trying to find a nice way of going about it.  I found this:

https://gist.github.com/489093 – by Philip Plante

which worked but meant lots of replicated code in every handler.  I’ve also modified the example to use Tornado’s newer gen way of doing things.

I’ve put my version here: https://gist.github.com/1370533 and is embedded below:

# Adapted from here: https://gist.github.com/489093
# Original credit goes to pplante and copyright notice pasted below
 
# Copyright (c) 2010, Philip Plante of EndlessPaths.com
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
 
 
# Modifications Copyright (c) 2011, Stephen Willey of cerealkillers.co.uk
# License remains as above
# Modifications allow it to be included once in multiple handlers.  Save it
# as async_process.py and put it in the path somewhere.  Use it like this:
#
# from handlers.base import BaseHandler
# 
# import tornado.web
# from tornado import gen
# from async_process import call_subprocess, on_subprocess_result
# 
# class ShellHandler(BaseHandler):
#     @tornado.web.asynchronous
#     @gen.engine
#     def get(self):
#         self.write("Before sleep<br />")
#         self.flush()
#         response = yield gen.Task(call_subprocess, self, "ls /")
#         self.write("Output is:\n%s" % (response.read(),))
#         self.finish()
#
 
import logging
import shlex
import subprocess
import tornado
 
def call_subprocess(context, command, callback=None):
    context.ioloop = tornado.ioloop.IOLoop.instance()
    context.pipe = p = subprocess.Popen(shlex.split(command), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, close_fds=True)
    context.ioloop.add_handler(p.stdout.fileno(), context.async_callback(on_subprocess_result, context, callback), context.ioloop.READ)
 
def on_subprocess_result(context, callback, fd, result):
    try:
        if callback:
            callback(context.pipe.stdout)
    except Exception, e:
        logging.error(e)
    finally:
        context.ioloop.remove_handler(fd)

Too Many Things To Try

Having a really short attention span and a wide range of interests makes for lots and lots of things to try. Now I just need to figure out what to do with some of these: