Chapter 9.9, Problem 9.7PP

Program Plan Intro

Dynamic allocator:

Dynamic allocator keeps the heap as a group of several size blocks; each block is an attached portion of virtual memory which is allocated or free.

• An allocated block has been clearly kept for use by the application.
• A free block is offered to be allocated.

Two types of allocators:

1. 1. Explicit allocators
2. 2. Implicit allocators

Explicit allocators:

Explicit allocators need the application to explicitly free any allocated blocks.

Implicit allocators:

Implicit allocators is the method of automatically releasing vacant allocated blocks. This is also known as garbage collection.

Implicit free list:

In this method, a block contains one word header, payload and additional padding. The header encrypts the block size, which contains header and padding; and check the block is allocated or free.

• If the arrangement is single-word, the block size is constantly a multiple of “4” and the low-order bits of the block size are always zero.
• If the arrangement is double word, the block size is constantly a multiple of “8” and the low-order bits of the block size are always zero.
• Thus, essential to store only the high-order “29 bits” of the block size, freeing the remaining “3 bits” to encrypt other information.
• Here, smallest significant bits is using to represent the block is allocated or free.