Implementation

Data Structures and Algorithms with Object-Oriented Design Patterns in C++

Implementation

Program declares the class DoublyLinkedPool. It is a concrete class derived from the abstract base class StoragePool. The public interface of the class comprises a constructor, the destructor, and the two member functions Acquire and Release. In addition, two private member functions, Unlink and InsertAfter are declared. These abstract common linked list manipulations.

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Program: DoublyLinkedPool Class Definition

The nested structures Header and Block are used to implement the layout shown in Figure . The Header structure contains information which appears in the first block of an area, regardless of whether it is reserved or free. In this case, the header comprises two members, status and length, packed into a single word of memory. The first member is a one-bit field of type Status. Status is an enumeration of the values reserved and free. The second field in the header, length, records the length in blocks of the associated area.

The Block structure contains a union. The union overlays an instance of the structure Links, which is used to hold pointers to the next and previous elements of the free list when the block is free, with the userPart of the block which is the space given to the user when the block is reserved.

In this implementation the size of a block (in bytes) is required to be at least

On a 32-bit machine the minimum block size is typically 12 bytes. In the implementation shown in Program , the size of the Block structure is set to 16 bytes.