my @array = ();
sub processA {
     push(@array,$some_data);
     common_stuff(); 
     # clear the array?   
}

sub processB {
     for(1 .. 1000) {
          push(@array,$some_data);
     }

     common_stuff();
     # clear the array?
}

sub common_stuff {
    foreach(@array) {
        #do stuff ...
    }
}