Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change
 
PerlMonks  

Re^7: disable functions if module not installed

by lepetitalbert (Monsignor)
on Nov 04, 2008 at 11:19 UTC ( #721349=note: print w/ replies, xml ) Need Help??


in reply to Re^6: disable functions if module not installed
in thread disable functions if module not installed

Hi Monks,

going nuts !

#!/usr/bin/perl -w use strict; use warnings; use diagnostics; eval { require Image::Magick }; my $is_Magick = $@ ? 0 : 1; print "Content-type: text/html; charset=ISO-8859-1\n\n"; print "<h1>$is_Magick</h1>";

which finally works on my XP box, now gives me

Deep recursion on subroutine "Image::Magick::Autoload"

and an out of memory ! on a debian server

has anyone a real working example ? an idea ? anything ? I cannot believe this can't be done !

thanks

Have a nice day !

"There is only one good, namely knowledge, and only one evil, namely ignorance." Socrates


Comment on Re^7: disable functions if module not installed
Select or Download Code
Re^8: disable functions if module not installed
by ikegami (Pope) on Nov 04, 2008 at 12:20 UTC

    AUTOLOAD is going into an infinite loop trying to reflect a constant, eating up the entire "C" stack. That's the memory you're running out of.

    I'm curious as to what is being autloaded. I'd add a print statement to Image/Magick.pm to print out $constname.

    The immediate cause of the problem is probably $! =~ /Invalid/ returning false when it is intended to return true. I'd add a print statement to Image/Magick.pm to print out (0+$!).":$!".

    Of course, that's assuming your version of Image::Magick is anything like the latest one. You haven't provided any version info.

    By the way,
    eval { require Image::Magick };
    my $is_Magick = $@ ? 0 : 1;
    is simpler and safer when written as
    my $is_Magick = eval { require Image::Magick; 1 };

      It seems like he didn't install imagemagick correctly (both perl bindings, and library)

        That's would cause bootstrap to die, setting $is_Magick to false. All's good.

        So what's calling AUTOLOAD?

        Hi ikegami and Anonymous Monk,

        ImageMagick-6.4.4-2 and perl 5.10, PerlMagick is installed by the IM installer.

        Everything worked fine with use Image::Magick.

        ikegami , added a print $constname here

        sub AUTOLOAD { # This AUTOLOAD is used to 'autoload' constants from the constant( +) # XS function. If a constant is not found then control is passed # to the AUTOLOAD in AutoLoader. my $constname; ($constname = $AUTOLOAD) =~ s/.*:://; print "\nDEBUG " . $constname . "\n";

        but nothing is printed. If I remove a concatenation point have an operator missing error. Did I put this in the wrong place ?

        And, after a server reboot, the script worked 2 times and then went OOM again !?

        thanks a lot and have a nice day !

        "There is only one good, namely knowledge, and only one evil, namely ignorance." Socrates
Re^8: disable functions if module not installed
by almut (Canon) on Nov 04, 2008 at 15:29 UTC

    Endless recursion would occur, if constant() is not being found - for whatever reason... Normally, the routine is provided by the XS code, but in case the wrong shared library is being loaded, or the symbol isn't exported properly, or something like that, the call to constant() would be routed to AUTOLOAD itself, leading to the next level of recursion...

    Quick proof of concept code:

    #!/usr/bin/perl package Image::Magick; sub AUTOLOAD { # This AUTOLOAD is used to 'autoload' constants from the constant( +) # XS function. If a constant is not found then control is passed # to the AUTOLOAD in AutoLoader. my $constname; ($constname = $AUTOLOAD) =~ s/.*:://; print STDERR "$constname "; # DEBUG my $val = constant($constname, @_ ? $_[0] : 0); # the following code from the original sub is irrelevant (never re +ached) #if ($! != 0) { # if ($! =~ /Invalid/) { # $AutoLoader::AUTOLOAD = $AUTOLOAD; # goto &AutoLoader::AUTOLOAD; # } # else { # my($pack,$file,$line) = caller; # die "Your vendor has not defined PerlMagick macro $pack\: +\:$constname, used at $file line $line.\n"; # } #} #eval "sub $AUTOLOAD { $val }"; #goto &$AUTOLOAD; } package main; Image::Magick::not_there(); # starts endless recursion

    I'm not sure why lepetitalbert's respective print statement doesn't print anything, but maybe it's just that STDOUT isn't connected to the terminal here, or some such...

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://721349]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others chilling in the Monastery: (3)
As of 2014-09-22 02:34 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    How do you remember the number of days in each month?











    Results (177 votes), past polls