** * implementation of {@link ppboundedfifo} which uses a circular array * internally. * * look at the documentation in ppboundedfifo to see how the methods are * supposed to work. * * the data is stored in the slots array. count is the number of items currently * in the fifo. when the fifo is not empty, head is the index of the next item * to remove. when the fifo is not full, tail is the index of the next available * slot to use for an added item. both head and tail need to jump to index 0 * when they "increment" past the last valid index of slots (this is what makes * it circular).