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Highlander - allow only one invocation at a time of an expensive CGI script

by merlyn (Sage)
on May 22, 2000 at 22:54 UTC ( #14260=snippet: print w/ replies, xml ) Need Help??

Description: My ISP's machine was overloaded this morning because a CGI script that uses a DBI connection was being invoked heavily (in response to a mass mailing of a newsletter). While the proper solution would have been to rewrite this to use mod_perl, I merely coded up a "highlander" solution using a sentinel file that gets flocked.
"You only have one life! If you value it, go home!" -- Connor MacLeod in Highlander
use CGI;
use Fcntl qw(LOCK_EX LOCK_NB);

open HIGHLANDER, ">>/tmp/renew.cgi.highlander" or die "Cannot open hig
+hlander: $!";
{
  my $count = 0;
  {
    flock HIGHLANDER, LOCK_EX | LOCK_NB and last;
    sleep 1;
    redo if ++$count < 10;
    ## couldn't get it after 10 seconds...
    my $host = $ENV{REMOTE_HOST};
    $host = $ENV{REMOTE_ADDR} unless defined $host;
    warn "$0 @ ".(localtime).": highlander abort for $host after 10 se
+conds\n";
    print CGI::header(-status => 503,
                      -retry_after => 30,
                      -type => 'text/plain'),
                        "Our server is overloaded.  Please try again i
+n a few minutes.\n";
    exit 0;
  }
}
## be sure to close HIGHLANDER at end of critical region if using mod_
+perl

Comment on Highlander - allow only one invocation at a time of an expensive CGI script
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RE: Highlander - allow only one invocation at a time of an expensive CGI script
by Simplicus (Monk) on May 23, 2000 at 19:08 UTC
    excellent. <q>There can be only one.</q>
    Simplicus
RE: Highlander - allow only one invocation at a time of an expensive CGI script
by rjimlad (Acolyte) on May 26, 2000 at 00:25 UTC
    A very impressive-looking script locking mechanism... I just have to wonder if there's a shorter way to do it...

    ----
    Arrr, Jim lad.

RE: Highlander - allow only one invocation at a time of an expensive CGI script
by nature (Initiate) on May 27, 2000 at 03:53 UTC
    I should point out that the need for this snip of code is "my fault" :-). The load comes from a SQL query and not from the perl code. Mod_perl was not an option here as eventually the code will be moved to a machine that does not run mod_perl (excuses, excuses). Regardless, since the query is what creates the load little could be gained by running it under mod_perl with respect to the load generated from the functionality. This is typically not the case as mod_perl often yeilds huge perfomance increases.
RE: Highlander - allow only one invocation at a time of an expensive CGI script
by lindex (Friar) on Jul 19, 2000 at 13:07 UTC
    Well I know that ISP your speaking of (I think) and I know that that was none of my code (i.e I used to work there)
    /****************************/ jason@gost.net, wh@ckz.org http://jason.gost.net /*****************************/

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