libflint/docs/memory.md

memory

Custom allocators and memory functions

Arena Allocator

A simple arena-style allocator

Structs

ArenaAllocator

Represents an arena allocator. ArenaAllocator holds its own buffer, but managing its size is left to the user. Like most structs in libflint, it must be malloc'd first before being passed to arena_init().

typedef struct {
    unsigned char* buf;
    size_t buf_sz;
    size_t offset_cur;
    size_t offset_prev;
} ArenaAllocator;

Functions

arena_init

Initializes the ArenaAllocator. The struct must first be created by the user using malloc(), see the example below. buf_sz is the size of the underlying buffer in bytes.

void arena_init(ArenaAllocator *allocator, size_t buf_sz);

/* Usage */
ArenaAllocator *a = malloc(sizeof(ArenaAllocator));
arena_init(a, 1024);

arena_free

Frees allocator and its underlying buffer. Users should set allocator to NULL after calling arena_free().

void arena_free(ArenaAllocator *allocator);

/* Usage */
arena_free(allocator);
allocator = NULL;

arena_clear

Resets the offset markers of the arena to 0, but does not wipe the underlying buffer. Technically, any assigned pointers will still work and

void arena_clear(ArenaAllocator *allocator);

*arena_malloc

Request memory of size bytes in length from the arena. Returns NULL if the assignment failed.

void *arena_malloc(ArenaAllocator* allocator, size_t size);

arena_resize_buf

Reallocates the underlying buffer in the arena to new_sz. You can grow or shrink the arena using this function. Any pointers allocated out of the arena are invalid after using this function.

void arena_resize_buf(ArenaAllocator *allocator, size_t new_sz);

*arena_resize

Resize an allocated pointer from the arena. See the example below for a simple use case

void *arena_resize(ArenaAllocator *allocator, void *mem, size_t old_sz, size_t new_sz);

/* Usage */
int *i = arena_malloc(a, sizeof(int));
*i = 1;
long *l = arena_resize(a, i1, sizeof(int), sizeof(long));
assert(*l == 1);

Macros

arena_sz

Convenience macro for getting the size of the arena's buffer

#define arena_sz(a) (a)->buf_sz

Pool Allocator

A pool-based allocator for chunks of the same size. Useful for quickly allocating and using memory of the same size without worrying about order; most operations are O(1)

Structs

PoolAllocator

Represents a pool allocator. PoolAllocator holds its own buffer, but managing its size is left to the user. Like most structs in libflint, it must be malloc'd first before being passed to pool_init().

typedef struct {
	unsigned char *buf;
    size_t buf_sz;
    size_t chunk_size;

    List *free_list;
} PoolAllocator;

Functions

pool_init

Initializes the PoolAllocator. The struct must first be created by the user using malloc(), see the example below.

• buf_sz: Size of the underlying buffer in bytes
• chunk_sz: Size of each chunk in bytes
• chunk_align: The alignment of the chunks. TheLF_DEFAULT_ALIGNMENT macro is available as a good default for basic types

void pool_init(PoolAllocator *allocator, size_t buf_sz, size_t chunk_sz, size_t chunk_align);

/* Usage */
PoolAllocator *pool = malloc(sizeof(PoolAllocator));
pool_init(pool, 64, 16, LF_DEFAULT_ALIGNMENT);

pool_free

Return a single chunk back to the pool. ptr is a pointer to the allocated chunk.

void pool_free(PoolAllocator *allocator, void *ptr);

pool_free_all

Returns all chunks back to the pool. Any pointers received before this call are now invalid and must be reasigned with pool_alloc or set to NULL.

void pool_free_all(PoolAllocator *allocator);

pool_alloc

Allocate a chunk from the pool. Returns NULL on failure.

void *pool_alloc(PoolAllocator *allocator);

pool_destroy

Destroys the underlying buffer and List in allocator, then frees it. User is responsible for setting allocator to NULL afterwards.

void pool_destroy(PoolAllocator *allocator);

Macros

pool_count_available

Returns the amount of chunks left available in the pool

#define pool_count_available(x) (x)->free_list->size

LF_DEFAULT_ALIGNMENT

The default alignment for allocators. Use this as a simple default (defaults to 16 bytes on amd64 systems) when storing basic types

#ifndef DEFAULT_ALIGNMENT
#define LF_DEFAULT_ALIGNMENT (2*sizeof(void*))
#endif // DEFAULT_ALIGNMENT