Memory pool (fixed-size block allocator) in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a memory pool (fixed-size block allocator)?

A memory pool is a way to manage memory by dividing a big chunk into many small fixed-size blocks. It helps quickly allocate and free memory without using the general heap.

beginner

Why use fixed-size blocks in a memory pool?

Fixed-size blocks make allocation and deallocation very fast and simple because each block is the same size. This avoids fragmentation and complex bookkeeping.

intermediate

How does a free list work in a memory pool?

A free list is a linked list of free blocks. When a block is freed, it is added back to the free list. When allocating, a block is taken from the free list.

intermediate

What happens if the memory pool runs out of free blocks?

If no free blocks are left, allocation fails or returns NULL. The program must handle this case to avoid crashes or memory errors.

intermediate

Show a simple C code snippet to initialize a memory pool with fixed-size blocks.

#define BLOCK_SIZE 32 #define BLOCK_COUNT 10 char pool[BLOCK_SIZE * BLOCK_COUNT]; void* free_list = NULL; void init_pool() { for (int i = 0; i < BLOCK_COUNT; i++) { void* block = &pool[i * BLOCK_SIZE]; *(void**)block = free_list; free_list = block; } }

What is the main advantage of using a fixed-size block memory pool?

A Automatically grows memory size

B Supports variable block sizes

C Uses less memory than heap

D Fast allocation and deallocation

Fixed-size blocks allow very fast allocation and freeing because the size is constant and bookkeeping is simple.

In a memory pool, what data structure usually tracks free blocks?

A Queue

B Binary tree

C Free list (linked list)

D Stack

A free list is a linked list that keeps track of all free blocks for quick allocation.

What should a program do if the memory pool has no free blocks left?

A Allocate from heap automatically

B Return NULL or error

C Overwrite existing blocks

D Ignore and continue

The program must handle allocation failure by returning NULL or an error to avoid crashes.

Which of these is NOT a benefit of fixed-size block allocators?

A Allows variable block sizes

B Simplifies allocation logic

C Avoids fragmentation

D Fast allocation speed

Fixed-size block allocators do NOT support variable block sizes; all blocks are the same size.

How is a block added back to the free list when freed?

A By linking it to the head of the free list

B By copying data to it

C By resizing the block

D By moving it to the end of the pool

The freed block is linked to the head of the free list for quick reuse.

Explain how a fixed-size block memory pool manages allocation and deallocation.

Think about how blocks are taken from and returned to the free list.

Describe what happens when the memory pool runs out of free blocks and how a program should handle it.

Consider what the allocator returns when no blocks are free.