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Start an asyncronous script from a cgi page?

I need to start a script that runs for a few hours using a cgi page. I can simply run the script from the browser, but the user will have to wait these few hours (and will most probably time out) and I don't want this. I want to be able to just run the script independantly of the browser...

Is there a way to do this? Say, can I schedule a cronjob with a cgi page? Or is there another solution?
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polygon
Asked:
polygon
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1 Solution
 
mehdiCommented:
Just take the nuts and bolts of what you need to do out of your "cgi-page" and put it into a regular perl file.  Set a cronjob to run that.  This is a very common systems administration task.

There is no reason why a cronjob would not work on your actual script.  Just beware that the execution of your code is not dependant on things such as:

* URL - your not passing parameters to the script with a GET string
* SERVER_NAME, and other environment variables which are quite often used from CGI scripts.

Hope that helps

Mehdi
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polygonAuthor Commented:
The cronjob thing works fine for me... But how do I set up a cronjob from within a cgi page (this may be a trivial question, but I am not much into Perl now :))).

I need to be able to set the cronjob to run at the moment (or maybe a few seconds after) the user clicks "Start the job" link...
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polygonAuthor Commented:
The cronjob thing works fine for me... But how do I set up a cronjob from within a cgi page (this may be a trivial question, but I am not much into Perl now :))).

I need to be able to set the cronjob to run at the moment (or maybe a few seconds after) the user clicks "Start the job" link...
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SapaCommented:
polygon,

which OS your CGI runs on?
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mehdiCommented:
Let me get this strait.. you want to put a scheduled task onto the system using perl ?

Well, your obviously using a unix based system the files you need to edit are in /var/spool/cron - something like that.

You can definately edit this file with perl - should not be a problem as long as your permissions are set up correctly - however this is not generally a good idea and i would advise against it.

Cheers

Mehdi

Mehdi
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SapaCommented:
> I need to start a script that runs for a few hours using a cgi page.

What the reason to use cron if you just want to run background process, not to postpone the launch until specified time?

On unix-like systems the only you need is fork another
proces from your CGI, and detach it. For example:


use CGI;
my $query = new CGI;
...

# Create unique filename for backgroung results
my $result_html = sprintf("%i%i.html", time, $$);

unless(defined(my $kid = fork)) {
    print $query->header;
    print "<H2>Cannot fork: $!</H2>";
}

if ($kid) {
    # Parent process
    print $query->header;
    print "<H2>Your request is processing now</H2><BR>";
    print "Please visit <A HREF=$result_html>";
    print "this link</A> 4 hours later";
    exit;
}

# child process

open STDIN, '< /dev/null';
open STDOUT, "> $result_html";
open STDERR, '> bgerror.log';

# execute your long code here

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mehdiCommented:
Hmm, i see what you are saying now..

im thinking - change the system time using perl - forcing your cronjob to gogo.. then set it back - your other process is underway and bobs your uncle..

That is a real HACK, but should work i think.

Im sure there is a better way to do it.. but cant think of it right now..

Mehdi
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mehdiCommented:
Hmm, i see what you are saying now..

im thinking - change the system time using perl - forcing your cronjob to gogo.. then set it back - your other process is underway and bobs your uncle..

That is a real HACK, but should work i think.

Im sure there is a better way to do it.. but cant think of it right now..

Mehdi
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mehdiCommented:
polygon,

Ive had a thought.

Why dont you change the way your program works altogether.

You are obviously carrying out a lengthy procedure based on user interaction through cgi.Your already asking the user to come back later (when the process completes) so why not do it this way,

* Get the user input and store it as "un-processed entries", tell the user to come back later, say an hour.
* set up a crongjob to run on the server every 30 minutes or so to process the unprocessed entries.
* When the cronjob is run, it processes "un-processed" entries and marks them as "processed".
* When the user returns they are shown the result of the processed entry (if its processed).  If the entry is not yet processed, they are told to come back later.

Hope that helps, though its not so much a solution - more a work around, but i think it achieves the same thing.

Mehdi
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mehdiCommented:
Poly,

Have you tried executing $test = `command.pl &`; ? note the backticks - execute a system command... the "&" should make it run in the background.

M

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