Arena Allocator in C: A Fixed-Memory-Pool Approach

Table of Contents

1. Introduction
2. The Fixed-Memory-Pool Arena Allocator
3. Anatomy of the Arena Allocator
4. Allocation and Management
5. Implementation of an Arena Allocator
6. Benefits and Use Cases
7. Conclusion

1 - Introduction

Memory management is a fundamental aspect of software development, especially in resource-constrained environments like embedded systems. Arena allocation, a memory management technique, offers an efficient alternative to dynamic memory allocation. In this article, we delve deeper into arena allocation with a focus on the fixed-memory-pool approach, exploring its benefits, use cases, and implementation details.

2 - The Fixed-Memory-Pool Arena Allocator

At the core of arena allocation is the concept of a fixed-memory pool. Instead of relying on dynamic memory allocation, a predetermined, static memory pool is allocated. This pool remains constant throughout the application's lifetime, making it a valuable choice for scenarios where dynamic allocation is less efficient or not advisable.

3 - Anatomy of the Arena Allocator

The arena allocator comprises key components:

Memory Pool Size

The size of the memory pool is defined upfront, representing the total available memory for allocation. This static allocation ensures a predictable and constant memory footprint.

Arena Structure

Each arena is encapsulated within an Arena structure, which contains:

• Memory Pool: The actual memory pool (data) where allocations occur.
• Used Memory: The amount of memory used (used) within the arena.
• Next Arena: A pointer to the next arena in the list. This linked structure allows for seamless expansion of the allocator as needed.

4 - Allocation and Management

Initializing Arenas

The arena_create function initializes a new arena, setting the used memory to 0 and preparing it for allocation. Notably, this initialization does not involve dynamic memory allocation. Instead, the memory pool is allocated statically.

Allocating Memory

The arena_alloc function is responsible for allocating memory from an arena. It enforces the constraint that the requested memory size must not exceed the remaining space in the arena's memory pool. If sufficient space is available, a pointer to the allocated memory is returned. This process repeats until the arena is fully utilized, after which a new arena can be added.

Arena Reset

In practice, a complete arena allocator would implement the arena_reset function to clean up the arena when it's no longer needed. This might involve releasing the memory associated with the arena or resetting the used memory to 0 for reuse.

5 - Implementation of an arena allocator

Here's an implementation of an arena allocator in C . We will manage a fixed pool of memory, and allocation will be performed from this pool.