5 thoughts on - Simplest Way Of Executing A Non-blocking (async) Python AGI Script?

• Write your python code to fork() the lookup to a child process, and let the parent return immediately to Asterisk.

  Not inside Asterisk, no.

  Antony.

• You have to use the “fork” command. This starts a copy of the process with all the same internal state including variables and filehandles. The command returns a non-zero value (which is the PID of the child process; you may need this, if you plan to outlive your children and have to clear their entries from the process table) to the parent process, and zero to the child process.
  So in the parent, you exit and return to the dialplan; and in the child, you close STDIN, STDOUT and STDERR (so no process is waiting for you to produce output), then just take your time doing what you have to. The parent is already long dead by this time, so exiting goes nowhere.

  Yes, fork! That is what the “&” operator is using “under the bonnet”.

• OK, I give up and come grovelling, “Fork” was suggested at 18:23, it’s now 22:20 and I have been through 4 different methods, all block with a 2 second delay before returning to dialplan.

  Here are just some of the examples I have tried, as as per the suggestions, I am closing all possible outputs in the forked process.

  https://docs.python.org/3.5/library/multiprocessing.html https://docs.python.org/3.5/library/multiprocessing.html?highlight=multiprocessing#multiprocessing.Process.join https://stackoverflow.com/questions/19747371/python-exit-commands-why-so-many-and-when-should-each-be-used https://stackoverflow.com/questions/27624850/launch-a-completely-independent-process https://stackoverflow.com/questions/13612434/why-are-the-methods-sys-exit-exit-raise-systemexit-not-working https://stackoverflow.com/questions/43280947/os-fork-share-local-variable-with-parent https://stackoverflow.com/questions/24052217/may-someone-explain-the-following-os-fork-example-to-me http://www.python-course.eu/forking.php https://pymotw.com/3/subprocess/
  http://code.activestate.com/recipes/186101-really-closing-stdin-stdout-stderr/

  This is the most likely looking code based on the examples. I would really, really appreciate a couple of pointers as to where I might be going wrong:

  #! /usr/bin/env python3
  # -*- coding: utf-8 -*-

  import multiprocessing as mp import time import sys import os

  #from asterisk.agi import AGI
  #agi = AGI()

  def f(name):
  sys.stdin.close()
  sys.stdout.close()
  sys.stderr.close()
  os.close(0) # close C’s stdin stream
  os.close(1) # close C’s stdout stream
  os.close(2) # close C’s stderr stream
  time.sleep(2)
  f = open(‘/var/lib/asterisk/agi-bin/tns/testing/testout.txt’, ‘w’)
  f.write(name)
  f.close()

  if __name__ == ‘__main__’:
  print(‘before process’)
  mp.set_start_method(‘fork’)
  q = mp.Queue()
  p = mp.Process(target=f, args=(‘asterisk’,))
  p.start()
  sys.exit()

• Take a look on that:

  https://issues.asterisk.org/jira/browse/ASTERISK-20532

  Regards, Marcelo H. Terres
  IM: mhterres@jabber.mundoopensource.com.br https://www.mundoopensource.com.br https://twitter.com/mhterres https://linkedin.com/in/marceloterres

• Oh wow – thank you SO much Marcelo.

  This works perfectly – exactly as I wanted. Don’t think I’d have figured it out, though.

  Well, that ticket says “not a bug” if this isn’t a bug, then
  “behaviour which differs dramatically from that which is expected”
  would definitely be the tag.

  Again, this fix works, and thank you!