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RE (4): Simple Locking

by tilly (Archbishop)
on Aug 09, 2000 at 00:08 UTC ( #26881=note: print w/replies, xml ) Need Help??


in reply to RE: RE (2): Simple Locking
in thread Simple Locking

Ah. In none of my code do I pass the locking name around, it usually is used to serialize specific programs.

All in all not significantly different from what merlyn did for Highlander - allow only one invocation at a time of an expensive CGI script. Which with this module would be:

use CGI; use Lock; local $main::highlander = Get Lock( lock_file => "highlander", timeout_limit => 10; ); unless ($main::highlander) { 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; } # No further logic required for mod_perl!!!
But I will definitely make the fix now that you have shown me that this really is a security hole and not merely a portability issue as I had thought.

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RE: RE (4): Simple Locking
by merlyn (Sage) on Aug 22, 2000 at 16:22 UTC
    You say mod_perl here, but what you really mean is Apache::Registry, just one of the many mod_perl modules, and you're relying on the trick that your code is getting wrapped into a giant subroutine, which may not necessarily be true in future implementations of Apache::Registry.

    Your trick doesn't work for mod_perl handlers in general, hence my warning on the original code.

    -- Randal L. Schwartz, Perl hacker

      Didn't know that. (I have mentioned I don't do much web stuff? Bad excuse, I know...)

      In general though, couldn't the above approach at least simplify the necessary logic somewhat? Particularly with functions with one entry and multiple exit points...?

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