I think you are barking up the wrong tree looking at %datahash as the cause of the problem.

The following simple script emulated what you are describing and once the 101 threads are up and running, the memory usage is rock steady under both 5.8.6/AS811 with the AS delivered core version of threads and 5.8.8/AS817 with the latest cpan versions of threads & threads::shared. And that's relying upon Perl's garbage collection alone.

More information needed. (I still suspect Data::Dump)

#! perl -slw
use threads;
use threads::shared;

print $threads::VERSION;
print $threads::shared::VERSION;
print $];

@th = map{
    threads->new(
        sub{
            while( 1 ){
                local %h = ( 1 .. 10000 );
                sleep 1
            }
        }
    )
} 1 .. 100;

$_->join for @th

__END__
c:\test>junk9
Name "main::h" used only once: possible typo at c:\test\junk9.pl line 
+13.
1.05
0.92
5.008006
Terminating on signal SIGINT(2)

c:\test>\AS817\perl\bin\perl5.8.8.exe junk9.pl
Name "main::h" used only once: possible typo at junk9.pl line 13.
1.1201
0.99
5.008008
Terminating on signal SIGINT(2)
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