mem_arena.h File Reference

High-performance virtual memory Arena Allocator. More...

#include "base/base_macros.h"
#include "base/base_types.h"

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Classes
struct	MemArena
	A virtual memory-backed linear allocator. More...
struct	MemArenaTemp
	A temporary snapshot of an arena's state. More...

Macros
#define	MEM_ARENA_ALIGNMENT   8
	The default byte alignment for memory pushed onto the arena.
#define	PUSH_STRUCT(arena, type)
	Type-Safe Allocation Macros.
#define	PUSH_ARRAY(arena, type, count)
	Pushes an array of structs of type T onto the arena.
#define	PUSH_STRUCT_ALIGNED(arena, type, alignment)
	Pushes a struct with custom memory alignment.
#define	PUSH_ARRAY_ALIGNED(arena, type, count, alignment)
	Pushes an array of structs with custom memory alignment.
#define	PUSH_CSTR(arena, cstr)
	Copies a NUL-terminated C string into the arena.

Typedefs
typedef struct MemArena	MemArena
	A virtual memory-backed linear allocator.
typedef struct MemArenaTemp	MemArenaTemp
	A temporary snapshot of an arena's state.

Functions
MemArena	mem_arena_create (usize reserve_size)
	Initializes a new virtual memory Arena.
void *	mem_arena_push (MemArena *arena, usize size)
	Allocates bytes sequentially on the arena without zeroing.
void *	mem_arena_push_zero (MemArena *arena, usize size)
	Allocates bytes and explicitly zero-initializes them.
void *	mem_arena_push_aligned (MemArena *arena, usize size, usize alignment)
	Allocates bytes with a specific custom alignment.
char *	mem_arena_push_cstr (MemArena *arena, const char *str, usize len)
	Copies a C string into the arena and appends a NUL terminator.
void	mem_arena_pop_to (MemArena *arena, usize pos)
	Rewinds the arena's pointer to a specific offset.
void	mem_arena_clear (MemArena *arena)
	Resets the arena pointer to zero, freeing all allocations in O(1).
void	mem_arena_clear_and_decommit (MemArena *arena)
	Clears the arena and returns all committed physical RAM to the OS.
void	mem_arena_release (MemArena *arena)
	Returns all virtual memory back to the operating system.
struct MemAllocator	mem_arena_allocator (MemArena *arena)
	Wraps a MemArena in the generic MemAllocator interface.
MemArenaTemp	mem_arena_temp_begin (MemArena *arena)
	Temporary Memory API.
void	mem_arena_temp_end (MemArenaTemp temp)
	Restores the arena to the position saved in temp.

Detailed Description

High-performance virtual memory Arena Allocator.

Reserves a massive block of virtual address space upfront but only commits physical RAM as the bump pointer advances. Eliminates individual malloc/free overhead and memory fragmentation entirely.

Allocation Model

This is a linear (bump) allocator. Individual allocations cannot be freed. Memory is reclaimed in bulk by resetting the position pointer via mem_arena_clear() or rolling back to a saved checkpoint via MemArenaTemp.

Basic Usage

// Reserve 1 GB of address space (no physical RAM used yet).
MemArena arena = mem_arena_create(GB(1));
 
// Allocate a single zeroed struct:
MyStruct *s = PUSH_STRUCT(&arena, MyStruct);
s->x = 10;
 
// Allocate a zeroed array:
float *buf = PUSH_ARRAY(&arena, float, 64);
 
// Scoped temporary memory — save, allocate, restore:
MemArenaTemp tmp = mem_arena_temp_begin(&arena);
char *scratch = PUSH_ARRAY(&arena, char, 4096);
// ... use scratch ...
mem_arena_temp_end(tmp); // arena snaps back to before tmp
 
// Per-frame reset — free everything at once, O(1):
mem_arena_clear(&arena);
 
// Return all virtual memory to the OS when done:
mem_arena_release(&arena);

Using as a MemAllocator

MemArena     arena = mem_arena_create(MB(64));
MemAllocator alloc = mem_arena_allocator(&arena);
 
// Now any API that takes MemAllocator works:
StringBuilder sb = {0};
sb_append(&sb, &alloc, STR8("hello"));

Copyright

2026 Alfred Jijo (MIT License)

Definition in file mem_arena.h.