wb_memory_arena.c

//wb_memory_arena.c
//by William Bundy

// A simple linear allocator using free and malloc
// Should use mmap on linux; calls to VirtualAlloc and VirtualFree are commented out
// arena_end_temp is technically broken; can be implemented much better with virtual memory

//This is free and unencumbered software released into the public domain.

#define LogError(...)

typedef const char* string;
typedef unsigned char u8;
typedef int64_t isize;
typedef int32_t i32; 

#define PAGE_SIZE 4096

typedef struct MemoryArena
{
	string name;
	u8* data;
	u8* head;
	u8* temp_head;
	u8* end;
	isize size;
	i32 was_bootstrapped;
	i32 align;
} MemoryArena;

static inline 
isize mem_align(isize p, isize n)
{
	isize mod = p & (n-1);
	return mod ? p + n - mod : p;
}

void arena_init(MemoryArena* arena, string name, isize size)
{
	arena->name = name;
	arena->align = 4;
	size = mem_align(size, PAGE_SIZE);
	arena->size = size;
	arena->data = malloc(size);//VirtualAlloc(NULL, size, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
	arena->end = arena->data + arena->size;
	arena->head = arena->data;
	arena->temp_head = NULL;
}

MemoryArena* arena_bootstrap(string name, isize size)
{
	MemoryArena local;
	size += sizeof(MemoryArena);
	arena_init(&local, name, size);
	MemoryArena* arena = arena_push(&local, sizeof(MemoryArena));
	*arena = local;
	arena->was_bootstrapped = 1;
	return arena;
}

void* arena_push(MemoryArena* arena, isize size)
{
	isize head = (isize)arena->head;
	isize newhead = mem_align(head + size, arena->align);
	if(newhead >= (isize)arena->end) {
		LogError(UserError, "[%s] was filled\n", arena->name);
		return NULL;
	}
	arena->head = (void*)newhead;

	return (void*)head;
}

void arena_start_temp(MemoryArena* arena)
{
	if(arena->temp_head != NULL) return;
	arena->temp_head = arena->head; 
	arena->head = (void*)mem_align((isize)arena->head, PAGE_SIZE);
}

void arena_end_temp(MemoryArena* arena)
{
	if(arena->temp_head == NULL) return;

	isize start = mem_align((isize)arena->temp_head, PAGE_SIZE);
	isize size = mem_align((isize)arena->head, PAGE_SIZE) - start;
	//VirtualFree((void*)start, size, MEM_DECOMMIT);
	//VirtualAlloc((void*)start, size, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
	memset(start, 0, size);

	arena->head = arena->temp_head;
	arena->temp_head = NULL;
}

void arena_clear(MemoryArena** arena)
{
	MemoryArena local = **arena;
	
	//VirtualFree(local.data, local.size, MEM_DECOMMIT);
	//VirtualAlloc(local.data, local.size, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
	free(local.data);
	local.data = malloc(local.size);
	local.head = local.data;

	if(local.was_bootstrapped) {
		*arena = ArenaPush(&local, sizeof(MemoryArena) + 64);
		**arena = local;
	}
}

MemoryArena arena_free(MemoryArena* arena)
{
	MemoryArena local = *arena;
	//VirtualFree(local.data, local.size, MEM_RELEASE);
	free(local.data)
	return local;
}
/*
This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org/>
*/