arena allocator

single-header arena allocator in C99

[Inspired by Untangling Lifetimes: The Arena Allocator]

Interface

• Functions take Arena references as arguments
• int initArena(*arena) initializes an arena, typically stack-allocated as shown in the example below
• void *palloc(*arena, size) is used like malloc
• void *pzalloc(*arena, size) is used like malloc, but zeroes using memset
• void *pGrowAlloc(*arena, *ptr, old_size, new_size) can grow allocations and copy contents, somewhat like realloc but only supporting increases in size
• char *pNewStr(*arena, *str) is like strcpy but allocates the new null-terminated string in the arena
• int resetArena(*arena) will free all pages, and initialize a new page using the last page size

Example

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

#define BIGNUM 20000

int main(void) {
	Arena p;
	initArena(&p);
	uint64_t **arr = palloc(&p, BIGNUM * sizeof(uint64_t*));

	for(uint64_t i = 0; i < BIGNUM; i++) {
		arr[i] = palloc(&p, BIGNUM * sizeof(uint64_t));
		for(uint64_t j = 0; j < BIGNUM; j++) {
			arr[i][j] = i * j;
		}
	}
	termArena(&p);
	return 0;
}

Settings

• MEMORY_HOG_FACTOR 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
• DEFAULT_PAGE_SIZE is the first page size upon initialization using initArena(). Default value 4096

Miscellaneous

• int setAllocator(fn_ptr) allows overriding malloc if desired. Replacement must be of the form void *(*alloc_fn)(size_t) (like malloc)
• getBytesUsed(*arena), getBytesAllocd(*arena), and printArenaInfo(*arena) can be used to retrieve or print usage information at runtime