SPUG: Web interface problem

[Melissa D. Binde]

You need to close both standard out and standard error after printing your
"this job is being processed message":

    close(STDOUT);
    close(STDERR);

that tells the web server that it's okay to continue.

Then fork twice to disassociate yourself from the parent process and set
yourself up as the leader of a new process group:

    if (!defined($pid = fork)) {
        &error_and_exit ("Unable to fork: $!\n");
    } elsif ($pid) {
        waitpid ($pid, 0);
        exit 0;
    }

    #
    # child.  fork again.
    #

    if (!defined($pid = fork)) {
        &error_and_exit ("Unable to fork: $!\n");
        exit 1;
    } elsif ($pid) {
        exit 0;
    }

    &POSIX::setsid();

My script can also be run from the command line (it behaves "correctly"
based on whether it's being called in a CGI context or not), so the double
forking and new process group may not be required for a web solution, I
don't know.  I'm sure someone here can answer, though.

The resulting disassociated process then emails the user when it's done.

Conversely, you can use a page that refreshes (simply the parent, in the
first fork there) to show current status to the user ("Yes/No" for
completion.)




Twas brillig, on Wed Mar 06 at 11:26:49 AM, and Daryn Nakhuda burbled:

> 
> I'd love to hear a good way to do this as well.. Fork seemed to keep the 
> little globe spinning in IE, but maybe I was doing it wrong. My hack to 
> make it seem okay to the end user was just to schedule an at job (+10 
> seconds) from the cgi, then tell them it was being processed. I then had 
> another place where you could check the status of jobs (the script being 
> run by at updated the database as it ran).
> 
> 
> 
> On Wed, 6 Mar 2002, Mikel Tidwell wrote:
> 
> > Hi everyone,
> > 
> > I'm stumped on how to proceed on a page for a web interface I'm creating
> > for my web site.  I want to be able to download a typically large file off
> > another web server, and store it on the local server.  By large, I mean an
> > average of 20 MB or so, but up to 100 MB at a typical rate of 30K/s.
> > 
> > Here's how I expect it to work:
> > 
> >  * User locates the file on another site, comes to the interface, and
> > commands the file be downloaded.
> >  * Script uses either LWP or `wget` to fetch file. <Problem>
> >  * Script moves on to allow the person how to name the file, etc.
> > 
> > Problem: Downloading a file usually takes more than two minutes.  If the
> > client doesn't time out by then, the web server will terminate the process
> > anyway (cgi time limit in Roxen).  I could simply change this limit, but
> > I'm looking for a smarter solution.
> > 
> > I thought about creating a child process, but I know very little about
> > fork(), or what happens to the parent in this scenario.  I also have an
> > issue with, should the child be able to download the file, notifying the
> > user that the download was complete, so he/she can continue.
> > 
> > If this still makes any sense, please help.  Thanks... ^^
> > 
> >  _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _
> >   -- Mikel Tidwell   President: RPGamer -- http://www.rpgamer.com/
> >    MSNM: FireMyst    Personal Home Page -- http://dragon.rpgamer.com/
> >  - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ - _ -
> > 
> > 
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> 
> 
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-M.

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     POST TO: spug-list at pm.org       PROBLEMS: owner-spug-list at pm.org
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  Replace ACTION by subscribe or unsubscribe, EMAIL by your Email-address
 For daily traffic, use spug-list for LIST ;  for weekly, spug-list-digest
     Seattle Perl Users Group (SPUG) Home Page: http://seattleperl.org