factor/vm/data_gc.c

#include "factor.h"

/* this function tests if a given faulting location is in a poison page. The
page address is taken from area + round_up_to_page_size(area_size) + 
 pagesize*offset */
bool in_page(void *fault, void *i_area, CELL area_size, int offset)
{
	const int pagesize = getpagesize();
	intptr_t area = (intptr_t) i_area;
	area += pagesize * ((area_size + (pagesize - 1)) / pagesize);
	area += offset * pagesize;

	const int page = area / pagesize;
	const int fault_page = (intptr_t)fault / pagesize;
	return page == fault_page;
}

void *safe_malloc(size_t size)
{
	void *ptr = malloc(size);
	if(ptr == 0)
		fatal_error("malloc() failed", 0);
	return ptr;
}

CELL object_size(CELL tagged)
{
	if(tagged == F || TAG(tagged) == FIXNUM_TYPE)
		return 0;
	else
		return untagged_object_size(UNTAG(tagged));
}

CELL untagged_object_size(CELL pointer)
{
	return align8(unaligned_object_size(pointer));
}

CELL unaligned_object_size(CELL pointer)
{
	switch(untag_header(get(pointer)))
	{
	case WORD_TYPE:
		return sizeof(F_WORD);
	case ARRAY_TYPE:
	case TUPLE_TYPE:
	case BIGNUM_TYPE:
	case BYTE_ARRAY_TYPE:
	case QUOTATION_TYPE:
		return array_size(array_capacity((F_ARRAY*)(pointer)));
	case HASHTABLE_TYPE:
		return sizeof(F_HASHTABLE);
	case VECTOR_TYPE:
		return sizeof(F_VECTOR);
	case STRING_TYPE:
		return string_size(string_capacity((F_STRING*)(pointer)));
	case SBUF_TYPE:
		return sizeof(F_SBUF);
	case RATIO_TYPE:
		return sizeof(F_RATIO);
	case FLOAT_TYPE:
		return sizeof(F_FLOAT);
	case COMPLEX_TYPE:
		return sizeof(F_COMPLEX);
	case DLL_TYPE:
		return sizeof(DLL);
	case ALIEN_TYPE:
		return sizeof(ALIEN);
	case WRAPPER_TYPE:
		return sizeof(F_WRAPPER);
	default:
		critical_error("Cannot determine untagged_object_size",pointer);
		return -1; /* can't happen */
	}
}

void primitive_size(void)
{
	drepl(tag_fixnum(object_size(dpeek())));
}

/* The number of cells from the start of the object which should be scanned by
the GC. Some types have a binary payload at the end (string, word, DLL) which
we ignore. */
CELL binary_payload_start(CELL pointer)
{
	switch(untag_header(get(pointer)))
	{
	/* these objects do not refer to other objects at all */
	case STRING_TYPE:
	case FLOAT_TYPE:
	case BYTE_ARRAY_TYPE:
	case BIGNUM_TYPE:
		return 0;
	/* these objects have some binary data at the end */
	case WORD_TYPE:
		return sizeof(F_WORD) - CELLS;
	case ALIEN_TYPE:
	case DLL_TYPE:
		return CELLS * 2;
	/* everything else consists entirely of pointers */
	default:
		return unaligned_object_size(pointer);
	}
}

void primitive_data_room(void)
{
	F_ARRAY *a = array(ARRAY_TYPE,gen_count,F);
	int gen;
	box_unsigned_cell(cards_end - cards);
	box_unsigned_cell(prior.limit - prior.base);
	for(gen = 0; gen < gen_count; gen++)
	{
		ZONE *z = &generations[gen];
		put(AREF(a,gen),make_array_2(tag_cell(z->limit - z->here),
			tag_cell(z->limit - z->base)));
	}
	dpush(tag_object(a));
}

/* Disables GC and activates next-object ( -- obj ) primitive */
void primitive_begin_scan(void)
{
	garbage_collection(TENURED,false);
	heap_scan_ptr = tenured.base;
	heap_scan = true;
}

/* Push object at heap scan cursor and advance; pushes f when done */
void primitive_next_object(void)
{
	CELL value = get(heap_scan_ptr);
	CELL obj = heap_scan_ptr;
	CELL type;

	if(!heap_scan)
		general_error(ERROR_HEAP_SCAN,F,F,true);

	if(heap_scan_ptr >= tenured.here)
	{
		dpush(F);
		return;
	}
	
	type = untag_header(value);
	heap_scan_ptr += untagged_object_size(heap_scan_ptr);

	if(type <= HEADER_TYPE)
		dpush(RETAG(obj,type));
	else
		dpush(RETAG(obj,OBJECT_TYPE));
}

/* Re-enables GC */
void primitive_end_scan(void)
{
	heap_scan = false;
}

/* scan all the objects in the card */
INLINE void collect_card(CARD *ptr, CELL here)
{
	CARD c = *ptr;
	CELL offset = (c & CARD_BASE_MASK);
	CELL card_scan = (CELL)CARD_TO_ADDR(ptr) + offset;
	CELL card_end = (CELL)CARD_TO_ADDR(ptr + 1);

	if(offset == 0x7f)
	{
		if(c == 0xff)
			critical_error("bad card",(CELL)ptr);
		else
			return;
	}

	while(card_scan < card_end && card_scan < here)
		card_scan = collect_next(card_scan);
	
	cards_scanned++;
}

INLINE void collect_gen_cards(CELL gen)
{
	CARD *ptr = ADDR_TO_CARD(generations[gen].base);
	CELL here = generations[gen].here;
	CARD *last_card = ADDR_TO_CARD(here);
	
	if(generations[gen].here == generations[gen].limit)
		last_card--;
	
	for(; ptr <= last_card; ptr++)
	{
		if(card_marked(*ptr))
			collect_card(ptr,here);
	}
}

void unmark_cards(CELL from, CELL to)
{
	CARD *ptr = ADDR_TO_CARD(generations[from].base);
	CARD *last_card = ADDR_TO_CARD(generations[to].here);
	if(generations[to].here == generations[to].limit)
		last_card--;
	for(; ptr <= last_card; ptr++)
		unmark_card(ptr);
}

void clear_cards(CELL from, CELL to)
{
	/* NOTE: reverse order due to heap layout. */
	CARD *last_card = ADDR_TO_CARD(generations[from].limit);
	CARD *ptr = ADDR_TO_CARD(generations[to].base);
	for(; ptr < last_card; ptr++)
		clear_card(ptr);
}

/* scan cards in all generations older than the one being collected */
void collect_cards(CELL gen)
{
	int i;
	for(i = gen + 1; i < gen_count; i++)
		collect_gen_cards(i);
}

/* Generational copying garbage collector */

CELL init_zone(ZONE *z, CELL size, CELL base)
{
	z->base = z->here = base;
	z->limit = z->base + size;
	z->alarm = z->base + (size * 3) / 4;
	return z->limit;
}

/* update this global variable. since it is stored in a non-volatile register,
we need to save its contents and re-initialize it when entering a callback,
and restore its contents when leaving the callback. see stack.c */
void update_cards_offset(void)
{
	cards_offset = (CELL)cards - (data_heap_start >> CARD_BITS);
}

/* input parameters must be 8 byte aligned */
/* the data heap layout is important:
- two semispaces: tenured and prior
- younger generations follow
there are two reasons for this:
- we can easily check if a pointer is in some generation or a younger one
- the nursery grows into the guard page, so allot() does not have to
check for out of memory, whereas allot_zone() (used by the GC) longjmp()s
back to collecting a higher generation */
void init_data_heap(CELL gens, CELL young_size, CELL aging_size)
{
	int i;
	CELL alloter;

	CELL total_size = (gens - 1) * young_size + 2 * aging_size;
	CELL cards_size = total_size / CARD_SIZE;

	gen_count = gens;
	generations = safe_malloc(sizeof(ZONE) * gen_count);

	data_heap_start = (CELL)(alloc_bounded_block(total_size)->start);
	data_heap_end = data_heap_start + total_size;

	cards = safe_malloc(cards_size);
	cards_end = cards + cards_size;
	update_cards_offset();

	alloter = data_heap_start;

	alloter = init_zone(&tenured,aging_size,alloter);
	alloter = init_zone(&prior,aging_size,alloter);

	for(i = gen_count - 2; i >= 0; i--)
		alloter = init_zone(&generations[i],young_size,alloter);

	clear_cards(NURSERY,TENURED);

	if(alloter != data_heap_start + total_size)
		fatal_error("Oops",alloter);

	heap_scan = false;
	gc_time = 0;
	minor_collections = 0;
	cards_scanned = 0;
}

void collect_callframe_triple(CELL *callframe,
	CELL *callframe_scan, CELL *callframe_end)
{
	*callframe_scan -= *callframe;
	*callframe_end -= *callframe;
	copy_handle(callframe);
	*callframe_scan += *callframe;
	*callframe_end += *callframe;
}

void collect_stack(BOUNDED_BLOCK *region, CELL top)
{
	CELL bottom = region->start;
	CELL ptr;

	for(ptr = bottom; ptr <= top; ptr += CELLS)
		copy_handle((CELL*)ptr);
}

void collect_callstack(BOUNDED_BLOCK *region, CELL top)
{
	CELL bottom = region->start;
	CELL ptr;

	for(ptr = bottom; ptr <= top; ptr += CELLS * 3)
		collect_callframe_triple((CELL*)ptr,
			(CELL*)ptr + 1, (CELL*)ptr + 2);
}

void collect_roots(void)
{
	int i;
	STACKS *stacks;

	copy_handle(&T);
	copy_handle(&bignum_zero);
	copy_handle(&bignum_pos_one);
	copy_handle(&bignum_neg_one);
	collect_callframe_triple(&callframe,&callframe_scan,&callframe_end);

	save_stacks();
	stacks = stack_chain;

	while(stacks)
	{
		collect_stack(stacks->data_region,stacks->data);
		collect_stack(stacks->retain_region,stacks->retain);
		
		collect_callstack(stacks->call_region,stacks->call);

		if(stacks->next != NULL)
		{
			collect_callframe_triple(&stacks->callframe,
				&stacks->callframe_scan,&stacks->callframe_end);
		}

		copy_handle(&stacks->catch_save);

		stacks = stacks->next;
	}

	for(i = 0; i < USER_ENV; i++)
		copy_handle(&userenv[i]);
}

/* Given a pointer to oldspace, copy it to newspace. */
INLINE void *copy_untagged_object(void *pointer, CELL size)
{
	void *newpointer;
	if(newspace->here + size >= newspace->limit)
		longjmp(gc_jmp,1);
	newpointer = allot_zone(newspace,size);
	memcpy(newpointer,pointer,size);
	return newpointer;
}

INLINE CELL copy_object_impl(CELL pointer)
{
	CELL newpointer = (CELL)copy_untagged_object((void*)UNTAG(pointer),
		object_size(pointer));

	/* install forwarding pointer */
	put(UNTAG(pointer),RETAG(newpointer,GC_COLLECTED));

	return newpointer;
}

/* follow a chain of forwarding pointers */
CELL resolve_forwarding(CELL untagged, CELL tag)
{
	CELL header = get(untagged);
	/* another forwarding pointer */
	if(TAG(header) == GC_COLLECTED)
		return resolve_forwarding(UNTAG(header),tag);
	/* we've found the destination */
	else
	{
		CELL pointer = RETAG(untagged,tag);
		if(should_copy(untagged))
			pointer = RETAG(copy_object_impl(pointer),tag);
		return pointer;
	}
}

/*
Given a pointer to a tagged pointer to oldspace, copy it to newspace.
If the object has already been copied, return the forwarding
pointer address without copying anything; otherwise, install
a new forwarding pointer.
*/
CELL copy_object(CELL pointer)
{
	CELL tag;
	CELL header;

	if(pointer == F)
		return F;

	tag = TAG(pointer);

	if(tag == FIXNUM_TYPE)
		return pointer;

	header = get(UNTAG(pointer));
	if(TAG(header) == GC_COLLECTED)
		return resolve_forwarding(UNTAG(header),tag);
	else
		return RETAG(copy_object_impl(pointer),tag);
}

INLINE void collect_object(CELL scan)
{
	CELL payload_start = binary_payload_start(scan);
	CELL end = scan + payload_start;

	scan += CELLS;

	while(scan < end)
	{
		copy_handle((CELL*)scan);
		scan += CELLS;
	}
}

CELL collect_next(CELL scan)
{
	CELL size = untagged_object_size(scan);
	collect_object(scan);
	return scan + size;
}

void reset_generations(CELL from, CELL to)
{
	CELL i;
	for(i = from; i <= to; i++)
		generations[i].here = generations[i].base;
	clear_cards(from,to);
}

void begin_gc(CELL gen)
{
	collecting_gen = gen;
	collecting_gen_start = generations[gen].base;

	if(gen == TENURED)
	{
		/* when collecting the oldest generation, rotate it
		with the semispace */
		ZONE z = generations[gen];
		generations[gen] = prior;
		prior = z;
		generations[gen].here = generations[gen].base;
		newspace = &generations[gen];
		clear_cards(TENURED,TENURED);
	}
	else
	{
		/* when collecting a younger generation, we copy
		reachable objects to the next oldest generation,
		so we set the newspace so the next generation. */
		newspace = &generations[gen + 1];
	}
}

void end_gc(CELL gen)
{
	if(gen == TENURED)
	{
		/* we did a full collection; no more
		old-to-new pointers remain since everything
		is in tenured space */
		unmark_cards(TENURED,TENURED);
		/* all generations except tenured space are
		now empty */
		reset_generations(NURSERY,TENURED - 1);

		fprintf(stderr,"*** Data GC (%ld minor, %ld cards)\n",
			minor_collections,cards_scanned);
		minor_collections = 0;
		cards_scanned = 0;
	}
	else
	{
		/* we collected a younger generation. so the
		next-oldest generation no longer has any
		pointers into the younger generation (the
		younger generation is empty!) */
		unmark_cards(gen + 1,gen + 1);
		/* all generations up to and including the one
		collected are now empty */
		reset_generations(NURSERY,gen);
		
		minor_collections++;
	}
}

/* collect gen and all younger generations */
void garbage_collection(CELL gen, bool code_gc)
{
	s64 start = current_millis();
	CELL scan;

	if(heap_scan)
		critical_error("GC disabled during heap scan",gen);

	/* we come back here if a generation is full */
	if(setjmp(gc_jmp))
	{
		if(gen == TENURED)
		{
			/* oops, out of memory */
			critical_error("Out of memory",0);
		}
		else
			gen++;
	}

	begin_gc(gen);

	/* initialize chase pointer */
	scan = newspace->here;

	/* collect objects referenced from stacks and environment */
	collect_roots();
	
	/* collect objects referenced from older generations */
	collect_cards(gen);

	/* collect literal objects referenced from compiled code */
	collect_literals();
	
	while(scan < newspace->here)
		scan = collect_next(scan);

	end_gc(gen);

	gc_time += (current_millis() - start);
}

void primitive_gc(void)
{
	bool code_gc = unbox_boolean();
	CELL gen = to_fixnum(dpop());
	if(gen <= NURSERY || code_gc)
		gen = NURSERY;
	else if(gen >= TENURED)
		gen = TENURED;
	garbage_collection(gen,code_gc);
}

/* WARNING: only call this from a context where all local variables
are also reachable via the GC roots. */
void maybe_gc(CELL size)
{
	if(nursery.here + size > nursery.alarm)
	{
		CELL gen = NURSERY;
		while(gen < TENURED)
		{
			ZONE *z = &generations[gen + 1];
			if(z->here < z->alarm)
				break;
			gen++;
		}

		garbage_collection(gen,false);
	}
}

void simple_gc(void)
{
	maybe_gc(0);
}

void primitive_gc_time(void)
{
	simple_gc();
	dpush(tag_bignum(s48_long_long_to_bignum(gc_time)));
}