asterisk users - Jun 2017 - Simplest way of executing a non-blocking (async) python AGI script?

I use a python AGI which pulls some info from a web service, which should
take half a second.

Sometimes, it takes 5-10 seconds which blocks the dialplan execution, but
the dialplan should continue immediately as it's not dependent on the
AGI/web service data.

What's the simplest, easiest quickest least-code way of firing off an AGI
with some variable, and then returning to the dialplan?

I've seen people talking about fastAGI, stasis, python ASYNC... all seems
rather complicated. I feel I must be missing something embarrassingly
obvious - isn't there just the equivalent of the unix shell's
"&"?!

Thanks.

(I'm using pyst2 if it matters)
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On Friday 30 June 2017 at 19:11:08, Jonathan H wrote:
> I use a python AGI which pulls some info from a web service, which should
> take half a second.
> 
> Sometimes, it takes 5-10 seconds which blocks the dialplan execution, but
> the dialplan should continue immediately as it's not dependent on the
> AGI/web service data.
> 
> What's the simplest, easiest quickest least-code way of firing off an
AGI
> with some variable, and then returning to the dialplan?
Write your python code to fork() the lookup to a child process, and let the 
parent return immediately to Asterisk.
> I've seen people talking about fastAGI, stasis, python ASYNC... all
seems
> rather complicated. I feel I must be missing something embarrassingly
> obvious - isn't there just the equivalent of the unix shell's
"&"?!
Not inside Asterisk, no.


Antony.

-- 
The words "e pluribus unum" on the Great Seal of the United States are
from a
poem by Virgil entitled "Moretum", which is about cheese and garlic
salad
dressing.

                                                   Please reply to the list;
                                                         please *don't* CC
me.

On Friday 30 Jun 2017, Jonathan H wrote:
> What's the simplest, easiest quickest least-code way of firing off an
AGI
> with some variable, and then returning to the dialplan?
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.
 
> I've seen people talking about fastAGI, stasis, python ASYNC... all
seems
> rather complicated. I feel I must be missing something embarrassingly
> obvious - isn't there just the equivalent of the unix shell's
"&"?!
Yes, fork!  That is what the "&" operator is using "under the
bonnet".

-- 
JKLM

Note:  Originating address only accepts e-mail from list!  If replying off-
list, change address to asterisk1list at earthshod dot co dot uk .

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()

On 30 June 2017 at 19:59, J Montoya or A J Stiles
<asterisk_list at earthshod.co.uk> wrote:
> On Friday 30 Jun 2017, Jonathan H wrote:
>> What's the simplest, easiest quickest least-code way of firing off
an AGI
>> with some variable, and then returning to the dialplan?
>
> 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.
>
>> I've seen people talking about fastAGI, stasis, python ASYNC... all
seems
>> rather complicated. I feel I must be missing something embarrassingly
>> obvious - isn't there just the equivalent of the unix shell's
"&"?!
>
> Yes, fork!  That is what the "&" operator is using
"under the bonnet".
>
> --
> JKLM
>
> Note:  Originating address only accepts e-mail from list!  If replying off-
> list, change address to asterisk1list at earthshod dot co dot uk .
>
> --
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