How can I completely delete a package in Perl?

Question

How do you completely delete a package in Perl? This means not only the package variables, but also any magic tables that Perl updates to handle inheritance changes and other things.

This simple test:

use warnings; use strict;
use Test::LeakTrace;
use Symbol 'delete_package';

leaktrace {
   package test;
   our $x = 1;

   package main;
   delete_package 'test';
};

results in the following output:

leaked ARRAY(0x81c930)  from /lib/perl5/5.10.1/Symbol.pm line 166.
leaked HASH(0x827760)   from /lib/perl5/5.10.1/Symbol.pm line 166.
leaked SCALAR(0x821920) from /lib/perl5/5.10.1/Symbol.pm line 166.

Using the -verbose flag for leaktrace results in screenfuls of data which I can post on request.

Things get worse if the line our @ISA = 'main'; is added to the test package:

leaked ARRAY(0x81cd10) from so.pl line 32.
leaked SCALAR(0x81c930) from so.pl line 32.
leaked ARRAY(0x8219d0) from so.pl line 32.
leaked HASH(0x8219c0) from so.pl line 32.
leaked SCALAR(0x8219b0) from so.pl line 32.
leaked HASH(0x8219a0) from so.pl line 32.
leaked SCALAR(0x821970) from /lib/perl5/5.10.1/Symbol.pm line 161.
leaked HASH(0x821950) from so.pl line 32.
leaked SCALAR(0x821940) from so.pl line 32.

Line 32 is where the our @ISA is.

To illustrate that these are indeed leaks and not just noise from the interpreter:

my $num = 0;
while (1) {
    no strict 'refs';
    @{$num.'::ISA'} = 'main';
    delete_package $num++;
}

will eat memory at a constant rate

So, is there a better way to get rid of a package than Symbol's delete_package? Is there something else that I have to do to help it along?

I have seen the same behavior in 5.8.8, 5.10.1, and 5.12

Answer 1

So this is a bug in perl, a reported one even as you discovered. Short of fixing that, it seems like your only way to avoid these leaks is to chose another approach to solve your problem.

How come you need a semi-anonymous package instead of, for example, a closure? Those are easy enough to make not leak, and, with some creativity, you can still implement pretty much every external interface on top of them, for example by blessing your closure coderefs and provide methods for them, providing overloading for them, etc.