Arena allocator

Features

• multiple regions
• allocated values are properly aligned
• mmap as underlying allocator

The capacity of arena itself and all its regions is always multiple of page size.

C23 is required. Just because I love nullptr. Plus, GNU extensions are required for mmap.

In notoriously stable Devuan this can be compiled with

clang-16 --std=gnu2x

(as of July 2024)

How to use

#include <stdio.h>
#include "arena.h"

int main(int argc, char* argv[])
{
    Arena *arena = create_arena(0);

    for(int i = 0; i < 500; i++) {
        arena_alloc(arena, 3, long long);
    }

    arena_fit(arena, 10, char);
    arena_fit(arena, 3000, char);

    arena_print(arena);
    delete_arena(arena);
}

API

Arena* create_arena(size_t capacity);

Create new arena with desired capacity or at least one page.

The capacity of subsequent regions will be same capacity unless adjusted with set_region_capacity.

void delete_arena(Arena* arena);

Free arena and all its regions.

void set_region_capacity(Arena* arena, size_t capacity);

Set desired capacity for newly created regions.

void* arena_alloc(Arena* arena, size_t num_elements, element_type_name);

Allocate properly aligned num_elements from the last region. If the last region has no space available, allocate new region.

void* arena_fit(Arena* arena, size_t num_elements, element_type_name);

Try to find a region with sufficient free space and allocate from it. If no region has space available, allocate new region.