for (...) {
   ...
   push(@forkArray, $level);
   push(@forkArray, $writeCounter);
   push(@forkArray, $nextMerge);
}

for (my $ct = 0; $ct <= $#forkArray; $ct+=3) {
   my $level      = $forkArray[$ct+0];
   my $mergeLast  = $forkArray[$ct+1];
   my $mergeFirst = $forkArray[$ct+2];
   ...
}

##</code><code>##

for (...) {
   ...
   push @forkArray, [ $level, $writeCounter, $nextMerge ];
}

foreach (@forkArray) {
   my ($level, $mergeLast, $mergeFirst) = $@_;
   ...
}