sub new {
    ...
    # [10] limiter
    (!$is_winenv && !$tid) ? MCE::Semaphore->new(3,1) : (),
    ...
}

sub _wait { 
    ...
    $obj->[10]->down if $obj->[10];    # limiter
    my ($parties, $synced, $timed_out, $aborted) = $obj->_up($flag);
    $obj->[10]->up   if $obj->[10];
    ...
}