use MCE::Simple -strict, (
    spawn_limit => 2,  # MCE::Child processes
    max_workers => 2,  # number of MCE workers
    init_relay  => 1,  # define to enable MCE::relay 
);

# Run MCE in the foreground.

mce_foreach my $i (10..18) {
    MCE::relay {
        # output orderly
        say "$$: $i";
    };
}

# Run MCE in the background.

spawn sub {
    mce_foreach my $i (20..28) {
        MCE::relay {
            say "$$: $i";
        };
    }
};

sync;

# Spin a worker per each input element.
# Up to "spawn_limit" will run simultaneously.
# Blocking otherwise, until next availability.

spawn my $i (30..38) {
    say "$$: $i";
}

sync;