tie my %hash, 'MCE::Shared';
    my $shared = MCE::Shared->hash();
    my $mutex = MCE::Mutex->new();

    $hash{number} = 0;   # 1 trip, store
    $shared->set( number => 0 );   # 1 trip

    # 2 trips fetch and store, needs a mutex
    $mutex->enter( $hash{number} += 2 );

    # 1 trip via the OO interface
    $shared->incrby( number => 2 );