public class ReadAheadInputStream
InputStream implementation which asynchronously reads ahead from the underlying input
stream when specified amount of data has been read from the current buffer. It does it by
maintaining two buffers - active buffer and read ahead buffer. Active buffer contains data
which should be returned when a read() call is issued. The read ahead buffer is used to
asynchronously read from the underlying input stream and once the current active buffer is
exhausted, we flip the two buffers so that we can start reading from the read ahead buffer
without being blocked in disk I/O.