Python fork() from within PHP

Aeiri · 10-02-2009, 10:29 PM

So basically, I have a PHP script that I want to execute a Python script from (both are my code), and I want to use fork() within Python to fork it into the background. The problem is that when I do this, the PHP script waits for the child to quit.

I have boiled this issue down to 2 files that illustrate the problem:

bgtest.php:

Code:

<?

$stdout = shell_exec("python bgtest.py; echo shell echo");
print_r($stdout);

?>

bgtest.py:

Code:

#!/usr/bin/env python

import os, time

if os.fork() == 0:
  time.sleep(2)
  print "child"

else:
  print "parent"

Calling the PHP outputs this:

Code:

$ php bgtest.php 
parent
shell echo
child

As you can see, the Python fork() works just fine since "shell echo" is output before the child output is.

So I've tried using exec(), shell_exec(), system(), etc from PHP and nothing changes it. I've tried using & and calling disown, but that doesn't work either.

I would really prefer a way that doesn't involve using fork() in PHP since this child is going to be a pretty hefty process so I don't want the overhead of an extra PHP process running (this is the main reason that I am making this fork into the background). I also would like to have the output of the parent process (This is to make sure everything executed okay. Basically it will have exception handling and report back to PHP).

I think the only way this will work is if PHP will completely ignore the fact that there is a child process and continue with its business, but I'm not sure how.

Thanks!

smeezekitty · 10-02-2009, 10:32 PM

i thought system() pauses the parent

Aeiri · 10-02-2009, 11:26 PM

Quote:

Originally Posted by smeezekitty

i thought system() pauses the parent

Okay, I didn't know that. Thank you for that information. I tried popen() instead:

Code:

<?

$p = popen("python bgtest.py", "r");
$stdout = stream_get_contents($p);
pclose($p);

print_r($stdout);

?>

...and it's still doing the same thing. Does popen() call system() as well?

smeezekitty · 10-02-2009, 11:33 PM

i dont know i am not a PHP guru and dont rely 100% on what i say
i just know the basic ins and outs of PHP and a fair amount of C and some C++

smeezekitty · 10-02-2009, 11:33 PM

i dont know i am not a PHP guru and dont rely 100% on what i say
i just know the basic ins and outs of PHP and a fair amount of C and some C++

ghostdog74 · 10-02-2009, 11:50 PM

what exactly are you wanting to do?

Aeiri · 10-03-2009, 10:42 AM

Quote:

Originally Posted by ghostdog74

what exactly are you wanting to do?

Well I thought I said it pretty clearly, but I guess I'll word it differently this time.

I am trying to execute a Python process from within PHP, and I want that Python process to fork(), where the parent returns to PHP that it successfully forked, and the child runs in the background on the server and does its tasks as a regular Python application.

Aeiri · 10-03-2009, 09:39 PM

I figured it out, somewhat. It's a bit hacky but it works.

Basically if you call exec() or anything from PHP, it checks to see if stdout/stderr is set to output to the "screen". If you redirect both to somewhere, such as /dev/null, it will immediately go to the next PHP statement. If you need the output of the parent process, the best way I can think of is to do: "&> file & echo !1" at the end. This will return the PID, and then you can monitor the status of the process with "ps" calls. Then you just read from the file you redirected to.

Hope this information helps someone.