ld58/code/core/impl/arena.c

void *M_ZeroSize(void *base, U64 size) {
	U8 *bytes = (U8 *) base;

	while (size--) {
		*bytes++ = 0;
	}

	return base;
}

void *M_CopySize(void *dst, void *src, U64 size) {
	U8 *se = (U8 *) src + (size - 1);
	U8 *de = (U8 *) dst + (size - 1);

	while (size--) {
		*de-- = *se--;
	}

	return dst;
}

M_Arena *_M_ArenaAlloc(U64 limit, M_ArenaOpts *opts) {
	M_Arena *result = 0;

	local_persist M_ArenaOpts _opts;
	if (!opts) {
		opts = &_opts;
	}

	U64 page_size   = VM_PageSize();
	U64 granularity = VM_AllocationGranularity();

	U64 reserve = Max(AlignUp(limit, granularity), granularity);
	U64 initial = Clamp(page_size, AlignUp(opts->initial, page_size), reserve);

	void *base = VM_Reserve(reserve);
	if (base != 0) {
		if (VM_Commit(base, initial)) {
			result = cast(M_Arena *) base;

			result->current = result;
			result->prev    = 0;

			result->base   = 0;
			result->offset = sizeof(M_Arena);
			result->limit  = reserve;

			result->committed = initial;
			result->increment = Max(AlignUp(opts->increment, page_size), page_size);

			result->flags = opts->flags;
		}
		else {
			VM_Release(base, reserve);
		}
	}

	Assert(result != 0);

	return result;
}

void *_M_ArenaPush(M_Arena *arena, U64 esize, M_ArenaPushOpts *opts) {
	void *result = 0;

	local_persist M_ArenaPushOpts _opts = { .count = 1, .align = 8 };
	if (!opts) {
		opts = &_opts;
	}

	U64 alignment    = Clamp(1, opts->align, 4096);
	M_Arena *current = arena->current;

	U64 total  = esize * opts->count;
	U64 offset = AlignUp(current->offset, alignment);
	U64 end    = offset + total;

	if (end > current->limit) {
		// Not enough space, chain a new arena if flags allow
		if ((arena->flags & M_ARENA_FIXED_SIZE) == 0) {
			U64 reserve   = Min(total + sizeof(M_Arena), M_ARENA_CHAIN_RESERVE);
			M_Arena *next = M_ArenaAlloc(reserve, .flags = arena->flags);

			next->base = current->base + current->limit;

			SLL_PushN(arena->current, next, prev);

			current = next;
			offset  = AlignUp(current->offset, alignment);
			end     = offset + total;
		}
	}

	if (end > current->committed) {
		// Not enough committed, commit more memory
		U64 commit_offset = AlignUp(end, current->increment);
		U64 commit_limit  = Min(commit_offset, current->limit);

		U8 *commit_base = cast(U8 *) current + current->committed;
		U64 commit_size = commit_limit - current->committed;

		if (VM_Commit(commit_base, commit_size)) {
			current->committed = commit_limit;
		}
	}

	if (end <= current->committed) {
		// Successfully got enough memory, push the allocation
		result = cast(U8 *) current + offset;
		current->offset = end;

		if (((opts->flags | arena->flags) & M_ARENA_NO_ZERO) == 0){
			M_ZeroSize(result, total);
		}
	}

	Assert(result != 0);
	Assert(((U64) result & (alignment - 1)) == 0);

	return result;
}

void *_M_ArenaPushCopy(M_Arena *arena, void *from, U64 size, M_ArenaPushOpts *opts) {
	void *result = M_CopySize(_M_ArenaPush(arena, size, opts), from, size);
	return result;
}

void M_ArenaReset(M_Arena *arena) {
	M_Arena *base = arena->current;
	while (base->base != 0) {
		M_Arena *prev = base->prev;

		VM_Release(base, base->limit);
		base = prev;
	}

	Assert(arena == base);

	// @Todo: We could decommit some of the memory in the base arena, do we want to give a
	// parameter to choose how much :decommit
	base->offset   = sizeof(M_Arena);
	arena->current = base;
}

void M_ArenaRelease(M_Arena *arena) {
	M_ArenaReset(arena);
	VM_Release(arena, arena->limit);
}

U64 M_ArenaOffset(M_Arena *arena) {
	U64 result = arena->current->base + arena->current->offset;
	return result;
}

void M_ArenaPop(M_Arena *arena, U64 offset) {
	M_Arena *base = arena->current;
	while (base->base > offset) {
		M_Arena *prev = base->prev;

		VM_Release(base, base->limit);
		base = prev;
	}

	// :decommit
	arena->current = base;
	base->offset   = Max(offset - base->base, sizeof(M_Arena));
}

void M_ArenaPopSize(M_Arena *arena, U64 size) {
	U64 offset = M_ArenaOffset(arena);
	offset -= Min(offset, size);

	M_ArenaPop(arena, offset);
}

#define M_TEMP_ARENA_LIMIT GB(4)
static thread_var M_Arena *__tls_temp[2];

M_Temp M_TempAcquire(U64 count, M_Arena **conflicts) {
	M_Temp result = { 0 };

	for (U32 it = 0; it < ArraySize(__tls_temp); ++it) {
		if (!__tls_temp[it]) {
			__tls_temp[it] = M_ArenaAlloc(M_TEMP_ARENA_LIMIT, .initial = MB(1), .increment = MB(1));
		}

		result.arena = __tls_temp[it];

		for (U32 c = 0; c < count; ++c) {
			if (__tls_temp[it] == conflicts[c]) {
				result.arena = 0;
				break;
			}
		}

		if (result.arena) {
			result.offset = M_ArenaOffset(result.arena);
			break;
		}
	}

	Assert(result.arena != 0);

	return result;
}

void M_TempRelease(M_Temp temp) {
	M_ArenaPop(temp.arena, temp.offset);
}