struct Queue:
    signed int size
    unsigned int consumer_index
    unsigned int producer_index
    unsigned int capacity

consumer:
    atomic dec size
    atomic read local_size := size

    if size < 0:
        atomic inc size
        ret Err
    else:
        atomic inc consumer_index
        read result := queue[consumer_index]
        ret Success(result)

producer:
    atomic inc size
    atomic read local_size := size

    if size > capacity:
        atomic dec size
        ret Err
    else:
        atomic inc producer_index
        put queue[consumer_index] := result
        ret Success