Writing a simple pool allocator in C

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2025-01-05 23:30:03

I found out about pool allocators some time ago, and I really liked its simplicity and high performance, so I decided to write my own. This article was initially inspired by Dmitry Soshnikov’s article.

Similarly to malloc, a pool allocator allows the user to allocate memory at run time. The pool allocator, however, is much faster than malloc, at the cost of having a fixed pool size. It allows the user to allocate and free memory blocks (referred to as chunks, from now on) in O(1) linear time. This implementation also uses very little memory: when creating the pool, a very small Pool structure is allocated, along with the pool itself. Free chunks are used to store information, so the memory impact is minimal.

Lastly, I would like to mention that this article is based on my ANSI C library for pool allocation, libpool. In the future, I might make small changes to the code on that repository and they won’t be reflected here, so feel free to check it out as well.

The following implementation corresponds to version v1.0.0 of my libpool library, with some notable “visual” differences (e.g. without ANSI restrictions). Some improvements, like being able to resize/reallocate an existing pool, will also be expanded below.