Launching a subprocess without waiting around for the result?

[erikcw]

Hi,

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

What is the correct way to launch subprocess without waiting for the
result to return?

Thanks!

[Ben Finney]

erikcw <er***********@gmail.comwrites:

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

For "how do I deal with subprocesses from Python", the (new in Python
2.4) 'subprocess' module is the default go-to answer
<URL:http://www.python.org/doc/lib/module-subprocess>, replacing a
rather fragmented set of modules before it.

What is the correct way to launch subprocess without waiting for the
result to return?

Creating an instance of 'subprocess.Popen' will launch the process and
return the Popen instance. You then have the option of polling it or
waiting for it to complete.

--
\ “To stay young requires unceasing cultivation of the ability to |
`\ unlearn old falsehoods.� —Robert Anson Heinlein |
_o__) |
Ben Finney

[erikcw]

On Sep 18, 3:33*pm, Ben Finney <[e-mail]>
wrote:

erikcw <[e-mail]:

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

For "how do I deal with subprocesses from Python", the (new in Python
2.4) 'subprocess' module is the default go-to answer
<URL:http://www.python.org/doc/lib/module-subprocess>, replacing a
rather fragmented set of modules before it.

What is the correct way to launch subprocess without waiting for the
result to return?

Creating an instance of 'subprocess.Popen' will launch the process and
return the Popen instance. You then have the option of polling it or
waiting for it to complete.

--
*\ * * “To stay young requires unceasing cultivation of the ability to |
* `\ * * * * * * * * * unlearn old falsehoods.” —Robert Anson Heinlein |
_o__) * * * * * * * * * * * * * * * * ** * * * * * * * * * * * * * * *|
Ben Finney

So if I create a Popen object and then just ignore the object and exit
the program the subproccess will finish it's work and then exit itself
cleanly?

[Ben Finney]

erikcw <er***********@gmail.comwrites:

On Sep 18, 3:33Â*pm, Ben Finney <[e-mail]>
wrote:

erikcw <[e-mail]:

What is the correct way to launch subprocess without waiting for
the result to return?

Creating an instance of 'subprocess.Popen' will launch the process
and return the Popen instance. You then have the option of polling
it or waiting for it to complete.

So if I create a Popen object and then just ignore the object and
exit the program the subproccess will finish it's work and then exit
itself cleanly?

Ah, no, that's a different thing. If the parent exits, the child will
also be killed I believe.

If you want to spawn a process and have it live on independent of the
parent, you want to make the child process a "daemon", detatching
itself from the parent's environment. I don't recall how that's done
immediately, but those are the terms to search for.

--
\ “Pinky, are you pondering what I'm pondering?� “Yes Brain, but |
`\ if our knees bent the other way, how would we ride a bicycle?� |
_o__) —_Pinky and The Brain_ |
Ben Finney

[John Fabiani]

erikcw wrote:

On Sep 18, 3:33Â*pm, Ben Finney <[e-mail]>
wrote:

>erikcw <[e-mail]:

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

For "how do I deal with subprocesses from Python", the (new in Python
2.4) 'subprocess' module is the default go-to answer
<URL:http://www.python.org/doc/lib/module-subprocess>, replacing a
rather fragmented set of modules before it.

What is the correct way to launch subprocess without waiting for the
result to return?

Creating an instance of 'subprocess.Popen' will launch the process and
return the Popen instance. You then have the option of polling it or
waiting for it to complete.

--
\ Â* Â* “To stay young requires unceasing cultivation of the ability to |
`\ Â* Â* Â* Â* Â* Â* Â* Â* Â* unlearn old falsehoods.â€� —Robert Anson Heinlein |
_o__) Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â*|
Ben Finney

So if I create a Popen object and then just ignore the object and exit
the program the subproccess will finish it's work and then exit itself
cleanly?

Just so happens that I ran into the same problem recently. I started with
exec(), then os.system(), next os.popen(), and last os.spawn().
This is what I discovered on a windows platform. The exec() replaced the
current running process. os.system did not start a completely new process.
os.popen() created a new process but did not open a command box to display
any print statements. Lastly os.spawn() worked - it created a new process
and opened a command box to display any print statements I needed.

Johnf

[r0g]

erikcw wrote:

Hi,

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

What is the correct way to launch subprocess without waiting for the
result to return?

Thanks!

Try exec() with " &" at the end of your command line.

Roger.

[r0g]

erikcw wrote:

Hi,

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

What is the correct way to launch subprocess without waiting for the
result to return?

Thanks!

Whoops, that was PHP! Imeant...

os.system(yourcommandline+" &")

;-)

Roger

[Marco Bizzarri]

On Fri, Sep 19, 2008 at 10:48 PM, Almar Klein <al*********@gmail.comwrote:

>Ah, no, that's a different thing. If the parent exits, the child will
also be killed I believe.

Not if it's stuck in some endless loop...

>If you want to spawn a process and have it live on independent of the
parent, you want to make the child process a "daemon", detatching
itself from the parent's environment. I don't recall how that's done
immediately, but those are the terms to search for.

I'm curious how this can be done, does anyone know this?

Almar

--
http://mail.python.org/mailman/listinfo/python-list

First result in "making a daemon in python with google":

http://mail.python.org/pipermail/pyt...ry/427692.html

(not tested)

Regards
Marco
--
Marco Bizzarri
http://notenotturne.blogspot.com/
http://iliveinpisa.blogspot.com/

[Gary Herron]

Almar Klein wrote:

>
Ah, no, that's a different thing. If the parent exits, the child will
also be killed I believe.
Not if it's stuck in some endless loop...

If you want to spawn a process and have it live on independent of the
parent, you want to make the child process a "daemon", detatching
itself from the parent's environment. I don't recall how that's done
immediately, but those are the terms to search for.
I'm curious how this can be done, does anyone know this?

I just dove into this several day ago for a small project.

On Linux it's easy -- it involves a couple of forks and other system
calls. Google for daemonize.py.
<http://github.com/lfittl/python-helpers/tree/master/daemonize.py>

On Windows, a bit of searching seems to find a consensus that the way to
do something similar is as a Window's service. I'm just now looking
into how to register and start a service, and how to stop and remove it
later. Google finds lots of information on this -- perhaps I'll post my
result when I've pulled it all together.

Gary Herron

[Michael Palmer]

On Sep 18, 5:33 pm, erikcw <[e-mail]:

Hi,

I have a cgi script where users are uploading large files for
processing. I want to launch a subprocess to process the file so the
user doesn't have to wait for the page to load.

What is the correct way to launch subprocess without waiting for the
result to return?

Thanks!

both os.spawn or subprocess can be used. I actually find subprocess
hard to remember so usually prefer os.spawn. For various examples and
explanations, see

http://effbot.org/librarybook/os.htm