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())));
}

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);
}

/* 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);
	}
}

/* Every object has a regular representation in the runtime, which makes GC
much simpler. Every slot of the object until binary_payload_start is a pointer
to some other object. */
INLINE void collect_object(CELL start)
{
	CELL scan = start;
	CELL payload_start = binary_payload_start(scan);
	CELL end = scan + payload_start;

	scan += CELLS;

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

	/* It is odd to put this hook here, but this is the only special case
	made for any type of object by the GC. If code GC is being performed,
	compiled code blocks referenced by this word must be marked. */
	if(collecting_code && object_type(start) == WORD_TYPE)
	{
		F_WORD *word = (F_WORD *)start;
		if(word->compiledp != F)
			recursive_mark(word->xt);
	}
}

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, bool code_gc)
{
	collecting_gen = gen;
	collecting_gen_start = generations[gen].base;
	collecting_code = code_gc;

	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()
{
	if(collecting_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,"*** %s GC (%ld minor, %ld cards)\n",
			collecting_code ? "Code and data" : "Data",
			minor_collections,cards_scanned);
		fflush(stderr);
		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(collecting_gen + 1,collecting_gen + 1);
		/* all generations up to and including the one
		collected are now empty */
		reset_generations(NURSERY,collecting_gen);
		
		minor_collections++;
	}
	
	if(collecting_code)
	{
		/* now that all reachable code blocks have been marked,
		deallocate the rest */
		free_unmarked(&compiling);
	}
}

/* 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,code_gc);

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

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

	if(!code_gc)
	{
		/* if we are doing code GC, then we will copy over literals
		from any code block which gets marked as live. if we are not
		doing code GC, just consider all literals as roots. */
		collect_literals();
	}

	while(scan < newspace->here)
		scan = collect_next(scan);

	end_gc();

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

void primitive_data_gc(void)
{
	CELL gen = to_fixnum(dpop());
	if(gen <= NURSERY)
		gen = NURSERY;
	else if(gen >= TENURED)
		gen = TENURED;
	garbage_collection(gen,false);
}

/* 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)));
}