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[nutballs]

I was about to embark on this on my own, but decided against it.

What I want is to call a script every minute via cron. - no problems there...

I want the script to check to see how many instances there are of a specific process, in particular a PHP script I am running from the CLI.
I want the script to maintain a total of 10 running. So if there are 7 already going, i want it to run that command 3 more times.
Ideally, I also want it to pay attention to the Load values. Lets say, 1min avg<1 (dual quads so.. technically 8 should be max i think)

I am not sure how to count the existing procs from script. I know how to view them, but not count them.
ps aux | grep "some special string"

also I have no idea how to do a loop. I am guessing its similar syntax actually to PHP. And frankly, i assume it could even be a PHP file that I run as the script from CLI instead of a .sh right? So if I can do PHP, I might be able to figure it out on my own. But a quick VS style 4 character magic code would be cool too.

[vsloathe]

Code:

ps aux | grep -c 'script_name'

Will return the number of processes running, plus one for the grep itself.

[nutballs]

-c    DUH
thanks V

seriously I think My --help keys are stuck

[nop_90]

WTF is this love of cron people have ?

Better to have one program.
Have the program fork/spawn all the child programs you need.

That way you can control the input/output/what ever.
You can also check exit code of function.

Fork is the best. As perks said, because of the way linux is setup. Extra forks do not take any extra memory.
(Hard to believe but it is true).

[nutballs]

im actually going to be moving towards that. An infinite loop that checks for processes and launches as needed, probably going to do it in PHP-cli.

I just have been currently using cron because it was there and worked with what i already had with little effort.

[perkiset]

WTF is this love of cron people have ?

LOL Because I don't want to have to re-code 5,10,25,30,55 * 1,3,5,6 1-6, *

cron is awesome as a timer when you don't want something to run * * * * *

[nop_90]

WTF is this love of cron people have ?

LOL Because I don't want to have to re-code 5,10,25,30,55 * 1,3,5,6 1-6, *

cron is awesome as a timer when you don't want something to run * * * * *

Ok so I was not the only one who experienced that

I remember once i played with cron. I wasted like 2 hours trying to get it work.
After I read about how great it was.
processes = []
while 1 :
        for p in processes :
             if p.exitcode == 0 :
                  do something
        time.sleep(30)
there all your logic done

[vsloathe]

I've always found CRON pretty straightforward...

[perkiset]

I agree, and I think that writing your own forker is important when you want sub-minute dispatch, but anything other than that cron is a gem IMO.

I write forkers only when I need something either interrupt driven or running much more than once per minute.

[arms]

python has a multi processing library that has a process pool implementation.
this way you can manage processes like a thread pool with n amount of worker processes.

if your language of choice doesn't have something this you could throw it together in python and have that script manage your php scripts.

http://docs.python.org/library/multiprocessing.html

backport for python 2.5:
http://code.google.com/p/python-multiprocessing/

[perkiset]

Hmmm... so you'd use Python as your daemon management daemon, correct? Is this what you'd do in the same situation?

[arms]

possibly. it's basically how i started using python. i wanted a shell script for something when i was still on windows and found python more intuitive and flexible than ms' bat syntax. then in linux, rather than learn sh i just converted over those python scripts.

but actually the library i linked to is not apropriate for this. it appears it's for running python functions in a subprocess.
 

the snippet nop posted is almost working python code and would be an easy solution.

[nop_90]

For what I am doing I use the multiprocessing module that arms talks about.
If you peek inside the code it just basically wraps the "fork" function.

As perks said. Amazingly enuff with increased forks your memory ussuage hardly goes up.
Ur processor ussuage will but not ur memory.

multiprocessing module is good if u are running same group of python "functions" etc.
There are a few crevates. Also if there is possibily that one of the subprocess with seg fault do not use shared memory.

If u want to do run "non-python" programs.
Then use subprocess
Advantage is u automatically have the stdin/stdout/stderr pipes attached

Code:

def runGocr(pilImage):
    io = StringIO.StringIO()
    pilImage.save(io,"ppm")
    imgStr = io.getvalue()
    io.close()
   
    p = subprocess.Popen(("gocr", "-"),
                          stdin = subprocess.PIPE,
                          stdout = subprocess.PIPE,
                          stderr = subprocess.PIPE,
                          close_fds = True)
   
    stdout_text, stderr_text = p.communicate(imgStr)
    return stdout_text.strip()

notice in the above snippit how the image is directly piped into GOCR using stdin.
Notice how the result is pulled out from stdout
In the above case it will block (which is what i want it to do) but you can check out module.

[arms]

i always use os.popen and just pass the command as a string, but this would save me a step of writing to file before.