boysenberry has asked for the wisdom of the Perl Monks concerning the following question:

I'm getting some "Attempt to free unreferenced scalar" errors while using mod_perl and am trying to use Devel::Leak and/or Devel::LeakTrace to find out which scalar references are off.

In the Devel::Leak doc it gives the following as an example: 
use Devel::Leak;
... setup code
my $count = Devel::Leak::NoteSV($handle);
... code that may leak
Devel::Leak::CheckSV($handle);

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In the above what would $handle be? I'm using my own PerlHandler in my httpd.conf file.

Replies are listed 'Best First'.
Re: Need Help gettng Devel::Leak working (or Devel::LeakTrace)
by Util (Priest) on Aug 20, 2005 at 19:37 UTC

    $handle is an output parameter; it is just a integer pointing to a block of memory that Devel::Leak::NoteSV is using to store its internal table. The documentation should probably read:

      use Devel::Leak;
  ... setup code

  my $handle;
  my $count = Devel::Leak::NoteSV($handle);

  ... code that may leak

  Devel::Leak::CheckSV($handle);

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    Also, be aware that most production builds of Perl do not have -DDEBUGGING turned on, and that the Devel::Leak documentation says:

    Note that you need a perl built with -DDEBUGGING for sv_dump() to print anything, but counts are valid in any perl.
    So, if you were expecting Devel::Leak::CheckSV to give you the details of the leaking objects (as I was when I played with it), you may be disappointed. You can use `perl -V | grep DEBUGGING` to check your build.

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      That is a problem for me actually. I'm using an OS X box and tried recompiling in the past with little success.

      Is there another way to track down leaked scalars?

      I have been able to get the mod_perl debugger working via
      httpd -X -DPERLDB

      [download]
      The "Attempt to free unreferenced scalar" errors I get are on apachectl stop or restart.
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Re: Need Help gettng Devel::Leak working (or Devel::LeakTrace)
by boysenberry (Acolyte) on Aug 20, 2005 at 22:42 UTC
    Ok so now I have: 
        my $this = {};
    bless( $this );

    my $count = Devel::Leak::NoteSV( $this->{handle} );

       ...application ( too much to list )

    Devel::Leak::CheckSV($this->{handle});

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    And in my error_log I'm getting:
    new 0xa29e18 :
    ...
    new 0x96f61c :
    old (1):
    0
    new 0xa0fe0c :
    ...
    new 0x9fabe4 :
    old (1):
    0
    new 0x9ffe30 :
    ...
    new 0x96f61c :
    old (1):
    0
    new 0xa00e18 :
    ...
    new 0x96f61c :
    old (1):
    0


    What does the old (1): 0 mean?
    Would that be causing the "Attempt to free unreferenced scalar" errors?
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