Ooops, you are right, this one gives memory use that agrees with the OP's original script. I think the sleep calls prevent the locking problem. At least on a faster machine. :-)

#!/usr/bin/perl
use threads;
use threads::shared;

my @a : shared;

for (1..10) { 
   sleep 1;
   threads->new(\&foo); 
   }

sleep 1;
system "grep VmSize /proc/$$/status";
<>;

sub foo {
   for (1..10) { push @a, " " x 1e6; }
   print @a . " elements in \@a\n";
}
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