A Practical Introduction to Data Structures and Algorithm Analysis

Sec. 8.3 Buffers and Buffer Pools 293Secondary Storage(on disk)01 7234567891538Main Memory(in RAM)Figure 8.5 An illustration of virtual memory. The complete collection of informationresides in the slower, secondary storage (on disk). Those sectors recentlyaccessed are held in the fast main memory (in RAM). In this example, copies ofSectors 1, 7, 5, 3, and 8 from secondary storage are currently stored in the mainmemory. If a memory access to Sector 9 is received, one of the sectors currentlyin main memory must be replaced.the buffer pool class itself. The first approach is to pass “messages” between thetwo. This approach is illustrated by the following abstract class:/** ADT for buffer pools using the message-passing style */public interface BufferPoolADT {/** Copy "sz" bytes from "space" to position "pos" in thebuffered storage */public void insert(byte[] space, int sz, int pos);}/** Copy "sz" bytes from position "pos" of the bufferedstorage to "space". */public void getbytes(byte[] space, int sz, int pos);This simple class provides an interface with two member functions, insertand getbytes. The information is passed between the buffer pool user and thebuffer pool through the space parameter. This is storage space, provided by thebufferpool client and at least sz bytes long, which the buffer pool can take informationfrom (the insert function) or put information into (the getbytesfunction). Parameter pos indicates where the information will be placed in the