use threads;
use strict;
use warnings;

for (;;) {
 my $thr = threads->new($sub1)->join;
 undef $thr;
}

##</code><code>##

i=0; while :; do A=$(ps -C threads3 -o ppid,pid,cmd,rss --no-headers); [ -n "$A" ] && echo $i $A || i=0 ; sleep 1; i=$(($i+1)); done

##</code><code>##

# $sub1 = sub { my $a=[ 1 .. 10000] };
1 19959 1137 /usr/bin/perl ./threads3 5276
2 19959 1137 /usr/bin/perl ./threads3 5140
3 19959 1137 /usr/bin/perl ./threads3 5700
[...]
642 19959 1137 /usr/bin/perl ./threads3 124244
643 19959 1137 /usr/bin/perl ./threads3 124736
644 19959 1137 /usr/bin/perl ./threads3 125380
# $sub1 = sub { my $a=[ 1 .. 100000] };
1 19959 8329 /usr/bin/perl ./threads3 24176
2 19959 8329 /usr/bin/perl ./threads3 24176
3 19959 8329 /usr/bin/perl ./threads3 24176
[...]
642 19959 8329 /usr/bin/perl ./threads3 28368
643 19959 8329 /usr/bin/perl ./threads3 26036
644 19959 8329 /usr/bin/perl ./threads3 34460
# $sub1 = sub { };
1 19959 13288 /usr/bin/perl ./threads3 3152
2 19959 13288 /usr/bin/perl ./threads3 3796
3 19959 13288 /usr/bin/perl ./threads3 4564
[...]
642 19959 13288 /usr/bin/perl ./threads3 400640
643 19959 13288 /usr/bin/perl ./threads3 401312
644 19959 13288 /usr/bin/perl ./threads3 401980