arena allocator

(not recommended due to lack of alignment)
updated to support alignment for cross-platform compatibility. speed untested

simple arena allocator in C99 with allocation alignment using alignof() macro

[Inspired by Untangling Lifetimes: The Arena Allocator]

Interface

• Functions take rkp_arena references as arguments
• int rkp_arena_init(rkp_arena *arena) initializes an arena, typically stack-allocated as shown in the example below. Data pages come from malloc
• void *rkp_arena_alloc(rkp_arena *arena, size_t size, size_t alignment) is used like malloc
• void *rkp_arena_zalloc(rkp_arena *arena, size_t size, size_t alignment) is used like malloc, but zeroes using memset
• void *rkp_arena_grow_alloc(void *ptr, size_t old_size, size_t new_size, rkp_arena *arena) can grow allocations and copy contents, somewhat like realloc but only supporting increases in size
• char *rkp_arena_new_str(char *str, rkp_arena *arena) is like strcpy but allocates the new null-terminated string within the specified arena
• int rkp_arena_reset(rkp_arena *arena) will free all pages, and initialize a new page using the last page size.

Failure Behavior

• exit() is called if malloc() fails

Example

#include <stdio.h>
#include <inttypes.h>
#include <stdalign.h>

#include "rkp_arena.h"

#define BIGNUM 20000

int main(void) {

	rkp_arena p;
	rkp_arena_init(&p);

	uint64_t **arr = rkp_arena_alloc(&p, BIGNUM * sizeof(uint64_t*), alignof(uint64_t *));

	for(uint64_t i = 0; i < BIGNUM; i++) {

		arr[i] = rkp_arena_alloc(&p, BIGNUM * sizeof(uint64_t), alignof(uint64_t));

		for(uint64_t j = 0; j < BIGNUM; j++) {
			arr[i][j] = i * j;
		}
	}
	rkp_arena_print_info(&p);
	rkp_arena_term(&p);
	return 0;
}

Settings

• #define MEMORY_HOG_FACTOR 8 will be multiplied by requested allocation size to determine new page size, in case the current page is not large enough. Larger values result in fewer overall calls to malloc. Default value 8
• #define DEF_BLOCK_SIZE 4096 is the first page size upon initialization using initArena(). Default value 4096

Miscellaneous

• rkp_arena_get_bytes_used, rkp_arena_get_bytes_allocd, and rkp_arena_print_info functions can be used to retrieve or print usage information at runtime