linux-packaging-mono/mono/metadata/sgen-tarjan-bridge.c

/*
 * sgen-tarjan-bridge.c: Tarjan-based bridge implementation.
 *
 * Copyright 2011 Novell, Inc (http://www.novell.com)
 * Copyright 2014 Xamarin Inc (http://www.xamarin.com)
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 *
 *
 * Copyright 2001-2003 Ximian, Inc
 * Copyright 2003-2010 Novell, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * 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 OR COPYRIGHT HOLDERS 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.
 */

#include "config.h"

#ifdef HAVE_SGEN_GC

#include <stdlib.h>

#include "sgen-gc.h"
#include "sgen-bridge.h"
#include "sgen-hash-table.h"
#include "sgen-qsort.h"
#include "tabledefs.h"
#include "utils/mono-logger-internal.h"
#include "utils/mono-time.h"
#include "utils/mono-compiler.h"


typedef struct {
	int size;
	int capacity;
	char *data;
} DynArray;

/*Specializations*/

typedef struct {
	DynArray array;
} DynPtrArray;

/* private */

static void
dyn_array_uninit (DynArray *da, int elem_size)
{
	if (da->capacity <= 0)
		return;

	sgen_free_internal_dynamic (da->data, elem_size * da->capacity, INTERNAL_MEM_BRIDGE_DATA);
	da->data = NULL;
}

static void
dyn_array_ensure_capacity (DynArray *da, int capacity, int elem_size)
{
	int old_capacity = da->capacity;
	char *new_data;

	if (capacity <= old_capacity)
		return;

	if (da->capacity == 0)
		da->capacity = 2;
	while (capacity > da->capacity)
		da->capacity *= 2;

	new_data = sgen_alloc_internal_dynamic (elem_size * da->capacity, INTERNAL_MEM_BRIDGE_DATA, TRUE);
	if (da->data) {
		memcpy (new_data, da->data, elem_size * da->size);
		sgen_free_internal_dynamic (da->data, elem_size * old_capacity, INTERNAL_MEM_BRIDGE_DATA);
	}
	da->data = new_data;
}

static void*
dyn_array_add (DynArray *da, int elem_size)
{
	void *p;

	dyn_array_ensure_capacity (da, da->size + 1, elem_size);

	p = da->data + da->size * elem_size;
	++da->size;
	return p;
}

/* ptr */

static void
dyn_array_ptr_uninit (DynPtrArray *da)
{
	dyn_array_uninit (&da->array, sizeof (void*));
}

static int
dyn_array_ptr_size (DynPtrArray *da)
{
	return da->array.size;
}

static void
dyn_array_ptr_set_size (DynPtrArray *da, int size)
{
	da->array.size = size;
}

static void*
dyn_array_ptr_get (DynPtrArray *da, int x)
{
	return ((void**)da->array.data)[x];
}

static void
dyn_array_ptr_add (DynPtrArray *da, void *ptr)
{
	void **p = dyn_array_add (&da->array, sizeof (void*));
	*p = ptr;
}

#define dyn_array_ptr_push dyn_array_ptr_add

static void*
dyn_array_ptr_pop (DynPtrArray *da)
{
	void *p;
	int size = da->array.size;
	g_assert (size > 0);
	p = dyn_array_ptr_get (da, size - 1);
	--da->array.size;
	return p;
}

static void
dyn_array_ptr_ensure_capacity (DynPtrArray *da, int capacity)
{
	dyn_array_ensure_capacity (&da->array, capacity, sizeof (void*));
}


static void
dyn_array_ptr_set_all (DynPtrArray *dst, DynPtrArray *src)
{
	if (src->array.size > 0) {
		dyn_array_ptr_ensure_capacity (dst, src->array.size);
		memcpy (dst->array.data, src->array.data, src->array.size * sizeof (void*));
	}
	dst->array.size = src->array.size;
}

static void
enable_accounting (void)
{
	// bridge_accounting_enabled = TRUE;
	// hash_table = (SgenHashTable)SGEN_HASH_TABLE_INIT (INTERNAL_MEM_BRIDGE_HASH_TABLE, INTERNAL_MEM_BRIDGE_HASH_TABLE_ENTRY, sizeof (HashEntryWithAccounting), mono_aligned_addr_hash, NULL);
}

static MonoGCBridgeObjectKind
class_kind (MonoClass *class)
{
	MonoGCBridgeObjectKind res = bridge_callbacks.bridge_class_kind (class);

	/* If it's a bridge, nothing we can do about it. */
	if (res == GC_BRIDGE_TRANSPARENT_BRIDGE_CLASS || res == GC_BRIDGE_OPAQUE_BRIDGE_CLASS)
		return res;

	/* Non bridge classes with no pointers will never point to a bridge, so we can savely ignore them. */
	if (!class->has_references) {
		SGEN_LOG (6, "class %s is opaque\n", class->name);
		return GC_BRIDGE_OPAQUE_CLASS;
	}

	/* Some arrays can be ignored */
	if (class->rank == 1) {
		MonoClass *elem_class = class->element_class;

		/* FIXME the bridge check can be quite expensive, cache it at the class level. */
		/* An array of a sealed type that is not a bridge will never get to a bridge */
		if ((elem_class->flags & TYPE_ATTRIBUTE_SEALED) && !elem_class->has_references && !bridge_callbacks.bridge_class_kind (elem_class)) {
			SGEN_LOG (6, "class %s is opaque\n", class->name);
			return GC_BRIDGE_OPAQUE_CLASS;
		}
	}

	return GC_BRIDGE_TRANSPARENT_CLASS;
}

//enable unsage logging
// #define DUMP_GRAPH 1

enum {
	INITIAL,
	SCANNED,
	FINISHED_ON_STACK,
	FINISHED_OFF_STACK
};

/*
Optimizations:
	We can split this data structure in two, those with bridges and those without
*/
typedef struct {
	DynPtrArray other_colors;
	DynPtrArray bridges;
	int api_index    : 31;
	unsigned visited : 1;
} ColorData;


typedef struct {
	MonoObject *obj; //XXX this can be eliminated.
	mword lock_word;

	ColorData *color;
	int index;
	int low_index : 27;

	unsigned state : 2;
	unsigned is_bridge : 1;
	unsigned obj_state : 2;
} ScanData;




static DynPtrArray scan_stack, loop_stack, registered_bridges;
static DynPtrArray color_merge_array;

static int ignored_objects;
static int object_index;
static int num_colors_with_bridges;
static int xref_count;

static size_t setup_time, tarjan_time, scc_setup_time, gather_xref_time, xref_setup_time, cleanup_time;
static SgenBridgeProcessor *bridge_processor;

#define BUCKET_SIZE 8184

//ScanData buckets
#define NUM_SCAN_ENTRIES ((BUCKET_SIZE - SIZEOF_VOID_P * 2) / sizeof (ScanData))

typedef struct _ObjectBucket ObjectBucket;
struct _ObjectBucket {
	ObjectBucket *next;
	ScanData *next_data;
	ScanData data [NUM_SCAN_ENTRIES];
};

static ObjectBucket *root_object_bucket;
static ObjectBucket *cur_object_bucket;
static int object_data_count;

static ObjectBucket*
new_object_bucket (void)
{
	ObjectBucket *res = sgen_alloc_internal (INTERNAL_MEM_TARJAN_OBJ_BUCKET);
	res->next_data = &res->data [0];
	return res;
}

static void
object_alloc_init (void)
{
	root_object_bucket = cur_object_bucket = new_object_bucket ();
}

static ScanData*
alloc_object_data (void)
{
	ScanData *res;
retry:

	/* next_data points to the first free entry */
	res = cur_object_bucket->next_data;
	if (res >= &cur_object_bucket->data [NUM_SCAN_ENTRIES]) {
		ObjectBucket *b = new_object_bucket ();
		cur_object_bucket->next = b;
		cur_object_bucket = b;
		goto retry;
	}
	cur_object_bucket->next_data = res + 1;
	object_data_count++;
	return res;
}

static void
free_object_buckets (void)
{
	ObjectBucket *cur = root_object_bucket;

	object_data_count = 0;

	while (cur) {
		ObjectBucket *tmp = cur->next;
		sgen_free_internal (cur, INTERNAL_MEM_TARJAN_OBJ_BUCKET);
		cur = tmp;
	}

	root_object_bucket = cur_object_bucket = NULL;
}

//ColorData buckets
#define NUM_COLOR_ENTRIES ((BUCKET_SIZE - SIZEOF_VOID_P * 2) / sizeof (ColorData))

typedef struct _ColorBucket ColorBucket;
struct _ColorBucket {
	ColorBucket *next;
	ColorData *next_data;
	ColorData data [NUM_COLOR_ENTRIES];
};

static ColorBucket *root_color_bucket;
static ColorBucket *cur_color_bucket;
static int color_data_count;


static ColorBucket*
new_color_bucket (void)
{
	ColorBucket *res = sgen_alloc_internal (INTERNAL_MEM_TARJAN_OBJ_BUCKET);
	res->next_data = &res->data [0];
	return res;
}

static void
color_alloc_init (void)
{
	root_color_bucket = cur_color_bucket = new_color_bucket ();
}

static ColorData*
alloc_color_data (void)
{
	ColorData *res;
retry:

	/* next_data points to the first free entry */
	res = cur_color_bucket->next_data;
	if (res >= &cur_color_bucket->data [NUM_COLOR_ENTRIES]) {
		ColorBucket *b = new_color_bucket ();
		cur_color_bucket->next = b;
		cur_color_bucket = b;
		goto retry;
	}
	cur_color_bucket->next_data = res + 1;
	color_data_count++;
	return res;
}

static void
free_color_buckets (void)
{
	ColorBucket *cur, *tmp;

	color_data_count = 0;

	for (cur = root_color_bucket; cur; cur = tmp) {
		ColorData *cd;
		for (cd = &cur->data [0]; cd < cur->next_data; ++cd) {
			dyn_array_ptr_uninit (&cd->other_colors);
			dyn_array_ptr_uninit (&cd->bridges);
		}
		tmp = cur->next;
		sgen_free_internal (cur, INTERNAL_MEM_TARJAN_OBJ_BUCKET);
	}
	root_color_bucket = cur_color_bucket = NULL;
}


static ScanData*
create_data (MonoObject *obj)
{
	mword *o = (mword*)obj;
	ScanData *res = alloc_object_data ();
	res->obj = obj;
	res->color = NULL;
	res->index = res->low_index = -1;
	res->obj_state = o [0] & SGEN_VTABLE_BITS_MASK;
	res->lock_word = o [1];

	o [0] |= SGEN_VTABLE_BITS_MASK;
	o [1] = (mword)res;
	return res;
}

static ScanData*
find_data (MonoObject *obj)
{
	ScanData *a = NULL;
	mword *o = (mword*)obj;
	if ((o [0] & SGEN_VTABLE_BITS_MASK) == SGEN_VTABLE_BITS_MASK)
		a = (ScanData*)o [1];
	return a;
}

static void
clear_after_processing (void)
{
	ObjectBucket *cur;

	for (cur = root_object_bucket; cur; cur = cur->next) {
		ScanData *sd;
		for (sd = &cur->data [0]; sd < cur->next_data; ++sd) {
			mword *o = (mword*)sd->obj;
			o [0] &= ~SGEN_VTABLE_BITS_MASK;
			o [0] |= sd->obj_state;
			o [1] = sd->lock_word;
		}
	}
}

static MonoObject*
bridge_object_forward (MonoObject *obj)
{
	MonoObject *fwd;
	mword *o = (mword*)obj;
	if ((o [0] & SGEN_VTABLE_BITS_MASK) == SGEN_VTABLE_BITS_MASK)
		return obj;

	fwd = SGEN_OBJECT_IS_FORWARDED (obj);
	return fwd ? fwd : obj;
}

#ifdef DUMP_GRAPH
static const char*
safe_name_bridge (MonoObject *obj)
{
	MonoVTable *vt = (MonoVTable*)SGEN_LOAD_VTABLE (obj);
	return vt->klass->name;
}

static ScanData*
find_or_create_data (MonoObject *obj)
{
	ScanData *entry = find_data (obj);
	if (!entry)
		entry = create_data (obj);
	return entry;
}
#endif

//----------
typedef struct {
	ColorData *color;
	int hash;
} HashEntry;

/*
We tried 2/32, 2/128, 4/32, 4/128, 6/128 and 8/128.

The performance cost between 4/128 and 8/128 is so small since cache movement happens completely in the same cacheline,
making the extra space pretty much free.

The cost between 32 and 128 itens is minimal too, it's mostly a fixed, setup cost.

Memory wise, 4/32 takes 512 and 8/128 takes 8k, so it's quite reasonable.
*/

#define ELEMENTS_PER_BUCKET 8
#define COLOR_CACHE_SIZE 128
static HashEntry merge_cache [COLOR_CACHE_SIZE][ELEMENTS_PER_BUCKET];

static int
mix_hash (size_t hash)
{
	return (int)(((hash * 215497) >> 16) ^ ((hash * 1823231) + hash));
}

static void
reset_cache (void)
{
	memset (merge_cache, 0, sizeof (merge_cache));
}


static gboolean
dyn_array_ptr_contains (DynPtrArray *da, void *x)
{
	int i;
	for (i = 0; i < dyn_array_ptr_size (da); ++i)
		if (dyn_array_ptr_get (da, i) == x)
			return TRUE;
	return FALSE;
}

static gboolean
match_colors (DynPtrArray *a, DynPtrArray *b)
{
	int i;
	if (dyn_array_ptr_size (a) != dyn_array_ptr_size (b))
		return FALSE;

	for (i = 0; i < dyn_array_ptr_size (a); ++i) {
		if (!dyn_array_ptr_contains (b, dyn_array_ptr_get (a, i)))
			return FALSE;
	}
	return TRUE;
}

static int cache_hits, cache_misses;

static ColorData*
find_in_cache (int *insert_index)
{
	HashEntry *bucket;
	int i, hash, size, index;

	size = dyn_array_ptr_size (&color_merge_array);
	/* Cache checking is very ineficient with a lot of elements*/
	if (size > 3)
		return NULL;

	hash = 0;
	for (i = 0 ; i < size; ++i)
		hash += mix_hash ((size_t)dyn_array_ptr_get (&color_merge_array, i));
	if (!hash)
		hash = 1;

	index = hash & (COLOR_CACHE_SIZE - 1);
	bucket = merge_cache [index];
	for (i = 0; i < ELEMENTS_PER_BUCKET; ++i) {
		if (bucket [i].hash != hash)
			continue;
		if (match_colors (&bucket [i].color->other_colors, &color_merge_array)) {
			++cache_hits;
			return bucket [i].color;
		}
	}

	//move elements to the back
	for (i = ELEMENTS_PER_BUCKET - 1; i > 0; --i)
		bucket [i] = bucket [i - 1];
	++cache_misses;
	*insert_index = index;
	bucket [0].hash = hash;
	return NULL;
}

static ColorData*
new_color (gboolean force_new)
{
	int i = -1;
	ColorData *cd;
	/* XXX Try to find an equal one and return it */
	if (!force_new) {
		cd = find_in_cache (&i);
		if (cd)
			return cd;
	}

	cd = alloc_color_data ();
	cd->api_index = -1;
	dyn_array_ptr_set_all (&cd->other_colors, &color_merge_array);
	/* if i >= 0, it means we prepared a given slot to receive the new color */
	if (i >= 0)
		merge_cache [i][0].color = cd;

	return cd;
}


static void
register_bridge_object (MonoObject *obj)
{
	create_data (obj)->is_bridge = TRUE;
}

static gboolean
is_opaque_object (MonoObject *obj)
{
	MonoVTable *vt = (MonoVTable*)SGEN_LOAD_VTABLE (obj);
	if ((vt->gc_bits & SGEN_GC_BIT_BRIDGE_OPAQUE_OBJECT) == SGEN_GC_BIT_BRIDGE_OPAQUE_OBJECT) {
		SGEN_LOG (6, "ignoring %s\n", vt->klass->name);
		++ignored_objects;
		return TRUE;
	}
	return FALSE;
}

static void
push_object (MonoObject *obj)
{
	ScanData *data;
	obj = bridge_object_forward (obj);

#if DUMP_GRAPH
	printf ("\t= pushing %p %s -> ", obj, safe_name_bridge (obj));
#endif

	/* Object types we can ignore */
	if (is_opaque_object (obj)) {
#if DUMP_GRAPH
		printf ("opaque\n");
#endif
		return;
	}

	data = find_data (obj);

	/* Already marked - XXX must be done this way as the bridge themselves are alive. */
	if (data && data->state != INITIAL) {
#if DUMP_GRAPH
		printf ("already marked\n");
#endif
		return;
	}

	/* We only care about dead objects */
	if (!data && sgen_object_is_live (obj)) {
#if DUMP_GRAPH
		printf ("alive\n");
#endif
		return;
	}

#if DUMP_GRAPH
	printf ("pushed!\n");
#endif

	if (!data)
		data = create_data (obj);
	g_assert (data->state == INITIAL);
	g_assert (data->index == -1);
	dyn_array_ptr_push (&scan_stack, data);
}

#undef HANDLE_PTR
#define HANDLE_PTR(ptr,obj)	do {					\
		MonoObject *dst = (MonoObject*)*(ptr);			\
		if (dst) push_object (dst); 			\
	} while (0)

static void
push_all (ScanData *data)
{
	MonoObject *obj = data->obj;
	char *start = (char*)obj;
	mword desc = sgen_obj_get_descriptor_safe (start);

#if DUMP_GRAPH
	printf ("**scanning %p %s\n", obj, safe_name_bridge (obj));
#endif

	#include "sgen-scan-object.h"
}


static void
compute_low_index (ScanData *data, MonoObject *obj)
{
	ScanData *other;
	ColorData *cd;
	obj = bridge_object_forward (obj);

	other = find_data (obj);

#if DUMP_GRAPH
	printf ("\tcompute low %p ->%p (%s) %p (%d / %d)\n", data->obj, obj, safe_name_bridge (obj), other, other ? other->index : -2, other ? other->low_index : -2);
#endif
	if (!other)
		return;

	g_assert (other->state != INITIAL);

	if ((other->state == SCANNED || other->state == FINISHED_ON_STACK) && data->low_index > other->low_index)
		data->low_index = other->low_index;

	/* Compute the low color */
	if (other->color == NULL)
		return;

	cd = other->color;
	if (!cd->visited) {
		dyn_array_ptr_add (&color_merge_array, other->color);
		cd->visited = TRUE;
	}
}

#undef HANDLE_PTR
#define HANDLE_PTR(ptr,obj)	do {					\
		MonoObject *dst = (MonoObject*)*(ptr);			\
		if (dst) compute_low_index (data, dst); 			\
	} while (0)

static void
compute_low (ScanData *data)
{
	MonoObject *obj = data->obj;
	char *start = (char*)obj;
	mword desc = sgen_obj_get_descriptor_safe (start);

	#include "sgen-scan-object.h"
}

static ColorData*
reduce_color (void)
{
	ColorData *color = NULL;
	int size = dyn_array_ptr_size (&color_merge_array);

	if (size == 0)
		color = NULL;
	else if (size == 1) {
		color = dyn_array_ptr_get (&color_merge_array, 0);
	} else
		color = new_color (FALSE);

	return color;
}

static void
create_scc (ScanData *data)
{
	int i;
	gboolean found = FALSE;
	gboolean found_bridge = FALSE;
	ColorData *color_data = NULL;

	for (i = dyn_array_ptr_size (&loop_stack) - 1; i >= 0; --i) {
		ScanData *other = dyn_array_ptr_get (&loop_stack, i);
		found_bridge |= other->is_bridge;
		if (found_bridge || other == data)
			break;
	}

#if DUMP_GRAPH
	printf ("|SCC rooted in %s (%p) has bridge %d\n", safe_name_bridge (data->obj), data->obj, found_bridge);
	printf ("\tpoints-to-colors: ");
	for (i = 0; i < dyn_array_ptr_size (&color_merge_array); ++i)
		printf ("%p ", dyn_array_ptr_get (&color_merge_array, i));
	printf ("\n");

	printf ("loop stack: ");
	for (i = 0; i < dyn_array_ptr_size (&loop_stack); ++i) {
		ScanData *other = dyn_array_ptr_get (&loop_stack, i);
		printf ("(%d/%d)", other->index, other->low_index);
	}
	printf ("\n");
#endif

	if (found_bridge) {
		color_data = new_color (TRUE);
		++num_colors_with_bridges;
	} else {
		color_data = reduce_color ();
	}

	while (dyn_array_ptr_size (&loop_stack) > 0) {
		ScanData *other = dyn_array_ptr_pop (&loop_stack);

#if DUMP_GRAPH
		printf ("\tmember %s (%p) index %d low-index %d color %p state %d\n", safe_name_bridge (other->obj), other->obj, other->index, other->low_index, other->color, other->state);
#endif

		other->color = color_data;
		switch (other->state) {
		case FINISHED_ON_STACK:
			other->state = FINISHED_OFF_STACK;
			break;
		case FINISHED_OFF_STACK:
			break;
		default:
			g_error ("Invalid state when building SCC %d", other->state);
		}

		if (other->is_bridge)
			dyn_array_ptr_add (&color_data->bridges, other->obj);

		if (other == data) {
			found = TRUE;
			break;
		}
	}
	g_assert (found);

	for (i = 0; i < dyn_array_ptr_size (&color_merge_array); ++i) {
		ColorData *cd  = dyn_array_ptr_get (&color_merge_array, i);
		g_assert (cd->visited);
		cd->visited = FALSE;
	}
	dyn_array_ptr_set_size (&color_merge_array, 0);
	found_bridge = FALSE;
}

static void
dfs (void)
{
	g_assert (dyn_array_ptr_size (&scan_stack) == 1);
	g_assert (dyn_array_ptr_size (&loop_stack) == 0);

	dyn_array_ptr_set_size (&color_merge_array, 0);

	while (dyn_array_ptr_size (&scan_stack) > 0) {
		ScanData *data = dyn_array_ptr_pop (&scan_stack);

		/**
		 * Ignore finished objects on stack, they happen due to loops. For example:
		 * A -> C
		 * A -> B
		 * B -> C
		 * C -> A
		 *
		 * We start scanning from A and push C before B. So, after the first iteration, the scan stack will have: A C B.
		 * We then visit B, which will find C in its initial state and push again.
		 * Finally after finish with C and B, the stack will be left with "A C" and at this point C should be ignored.
         *
         * The above explains FINISHED_ON_STACK, to explain FINISHED_OFF_STACK, consider if the root was D, which pointed
		 * to A and C. A is processed first, leaving C on stack after that in the mentioned state.
		 */
		if (data->state == FINISHED_ON_STACK || data->state == FINISHED_OFF_STACK)
			continue;

		if (data->state == INITIAL) {
			g_assert (data->index == -1);
			g_assert (data->low_index == -1);

			data->state = SCANNED;
			data->low_index = data->index = object_index++;
			dyn_array_ptr_push (&scan_stack, data);
			dyn_array_ptr_push (&loop_stack, data);

#if DUMP_GRAPH
			printf ("+scanning %s (%p) index %d color %p\n", safe_name_bridge (data->obj), data->obj, data->index, data->color);
#endif
			/*push all refs */
			push_all (data);
		} else {
			g_assert (data->state == SCANNED);
			data->state = FINISHED_ON_STACK;

#if DUMP_GRAPH
			printf ("-finishing %s (%p) index %d low-index %d color %p\n", safe_name_bridge (data->obj), data->obj, data->index, data->low_index, data->color);
#endif

			/* Compute low index */
			compute_low (data);

#if DUMP_GRAPH
			printf ("-finished %s (%p) index %d low-index %d color %p\n", safe_name_bridge (data->obj), data->obj, data->index, data->low_index, data->color);
#endif
			//SCC root
			if (data->index == data->low_index)
				create_scc (data);
		}
	}
}

static void
register_finalized_object (MonoObject *obj)
{
	g_assert (sgen_need_bridge_processing ());
	dyn_array_ptr_push (&registered_bridges, obj);
}

static void
reset_data (void)
{
	dyn_array_ptr_set_size (&registered_bridges, 0);
}

static void
cleanup (void)
{
	dyn_array_ptr_set_size (&scan_stack, 0);
	dyn_array_ptr_set_size (&loop_stack, 0);
	dyn_array_ptr_set_size (&registered_bridges, 0);
	free_object_buckets ();
	free_color_buckets ();
	reset_cache ();
	object_index = 0;
	num_colors_with_bridges = 0;
}

#ifdef DUMP_GRAPH
static void
dump_color_table (const char *why, gboolean do_index)
{
	ColorBucket *cur;
	int i = 0, j;
	printf ("colors%s:\n", why);

	for (cur = root_color_bucket; cur; cur = cur->next, ++i) {
		ColorData *cd;
		for (cd = &cur->data [0]; cd < cur->next_data; ++cd) {
			if (do_index)
				printf ("\t%d(%d):", i, cd->api_index);
			else
				printf ("\t%d: ", i);
			for (j = 0; j < dyn_array_ptr_size (&cd->other_colors); ++j) {
				printf ("%p ", dyn_array_ptr_get (&cd->other_colors, j));
			}
			if (dyn_array_ptr_size (&cd->bridges)) {
				printf (" bridges: ");
				for (j = 0; j < dyn_array_ptr_size (&cd->bridges); ++j) {
					MonoObject *obj = dyn_array_ptr_get (&cd->bridges, j);
					ScanData *data = find_or_create_data (obj);
					printf ("%d ", data->index);
				}
			}
			printf ("\n");
		}
	}

}
#endif

static gint64
step_timer (gint64 *timer)
{
	gint64 curtime, diff;

	SGEN_TV_GETTIME (curtime); 
	diff = SGEN_TV_ELAPSED (*timer, curtime);
	*timer = curtime;
	return diff;
}
static void
processing_stw_step (void)
{
	int i;
	int bridge_count;
	gint64 curtime;

	if (!dyn_array_ptr_size (&registered_bridges))
		return;

#if defined (DUMP_GRAPH)
	printf ("-----------------\n");
#endif
	/*
	 * bridge_processing_in_progress must be set with the world
	 * stopped.  If not there would be race conditions.
	 */
	bridge_processing_in_progress = TRUE;

	SGEN_TV_GETTIME (curtime);

	object_alloc_init ();
	color_alloc_init ();

	bridge_count = dyn_array_ptr_size (&registered_bridges);
	for (i = 0; i < bridge_count ; ++i)
		register_bridge_object (dyn_array_ptr_get (&registered_bridges, i));

	setup_time = step_timer (&curtime);

	for (i = 0; i < bridge_count; ++i) {
		ScanData *sd = find_data (dyn_array_ptr_get (&registered_bridges, i));
		if (sd->state == INITIAL) {
			dyn_array_ptr_push (&scan_stack, sd);
			dfs ();
		} else {
			g_assert (sd->state == FINISHED_OFF_STACK);
		}
	}

	tarjan_time = step_timer (&curtime);

#if defined (DUMP_GRAPH)
	printf ("----summary----\n");
	printf ("bridges:\n");
	for (i = 0; i < bridge_count; ++i) {
		ScanData *sd = find_data (dyn_array_ptr_get (&registered_bridges, i));
		printf ("\t%s (%p) index %d color %p\n", safe_name_bridge (sd->obj), sd->obj, sd->index, sd->color);
	}

	dump_color_table (" after tarjan", FALSE);
#endif

	clear_after_processing ();
}


static void
gather_xrefs (ColorData *color)
{
	int i;
	for (i = 0; i < dyn_array_ptr_size (&color->other_colors); ++i) {
		ColorData *src = dyn_array_ptr_get (&color->other_colors, i);
		if (src->visited)
			continue;
		src->visited = TRUE;
		if (dyn_array_ptr_size (&src->bridges))
			dyn_array_ptr_add (&color_merge_array, src);
		else
			gather_xrefs (src);
	}
}

static void
reset_xrefs (ColorData *color)
{
	int i;
	for (i = 0; i < dyn_array_ptr_size (&color->other_colors); ++i) {
		ColorData *src = dyn_array_ptr_get (&color->other_colors, i);
		if (!src->visited)
			continue;
		src->visited = FALSE;
		if (!dyn_array_ptr_size (&src->bridges))
			reset_xrefs (src);
	}
}

static void
processing_build_callback_data (int generation)
{
	int j, api_index;
	MonoGCBridgeSCC **api_sccs;
	MonoGCBridgeXRef *api_xrefs;
	gint64 curtime;
	ColorBucket *cur;

	g_assert (bridge_processor->num_sccs == 0 && bridge_processor->num_xrefs == 0);
	g_assert (!bridge_processor->api_sccs && !bridge_processor->api_xrefs);

	if (!dyn_array_ptr_size (&registered_bridges))
		return;

	SGEN_TV_GETTIME (curtime);

	/*create API objects */

#if defined (DUMP_GRAPH)
	printf ("***** API *****\n");
	printf ("number of SCCs %d\n", num_colors_with_bridges);
#endif

	/* This is a straightforward translation from colors to the bridge callback format. */
	api_sccs = sgen_alloc_internal_dynamic (sizeof (MonoGCBridgeSCC*) * num_colors_with_bridges, INTERNAL_MEM_BRIDGE_DATA, TRUE);
	api_index = xref_count = 0;

	for (cur = root_color_bucket; cur; cur = cur->next) {
		ColorData *cd;
		for (cd = &cur->data [0]; cd < cur->next_data; ++cd) {
			int bridges = dyn_array_ptr_size (&cd->bridges);
			if (!bridges)
				continue;

			api_sccs [api_index] = sgen_alloc_internal_dynamic (sizeof (MonoGCBridgeSCC) + sizeof (MonoObject*) * bridges, INTERNAL_MEM_BRIDGE_DATA, TRUE);
			api_sccs [api_index]->is_alive = FALSE;
			api_sccs [api_index]->num_objs = bridges;

			cd->api_index = api_index;

			for (j = 0; j < bridges; ++j)
				api_sccs [api_index]->objs [j] = dyn_array_ptr_get (&cd->bridges, j);
			api_index++;
		}
	}

	scc_setup_time = step_timer (&curtime);

	for (cur = root_color_bucket; cur; cur = cur->next) {
		ColorData *cd;
		for (cd = &cur->data [0]; cd < cur->next_data; ++cd) {
			int bridges = dyn_array_ptr_size (&cd->bridges);
			if (!bridges)
				continue;

			dyn_array_ptr_set_size (&color_merge_array, 0);
			gather_xrefs (cd);
			reset_xrefs (cd);
			dyn_array_ptr_set_all (&cd->other_colors, &color_merge_array);
			xref_count += dyn_array_ptr_size (&cd->other_colors);
		}
	}

	gather_xref_time = step_timer (&curtime);

#if defined (DUMP_GRAPH)
	printf ("TOTAL XREFS %d\n", xref_count);
	dump_color_table (" after xref pass", TRUE);
#endif

	api_xrefs = sgen_alloc_internal_dynamic (sizeof (MonoGCBridgeXRef) * xref_count, INTERNAL_MEM_BRIDGE_DATA, TRUE);
	api_index = 0;
	for (cur = root_color_bucket; cur; cur = cur->next) {
		ColorData *src;
		for (src = &cur->data [0]; src < cur->next_data; ++src) {
			int bridges = dyn_array_ptr_size (&src->bridges);
			if (!bridges)
				continue;

			for (j = 0; j < dyn_array_ptr_size (&src->other_colors); ++j) {
				ColorData *dest = dyn_array_ptr_get (&src->other_colors, j);
				g_assert (dyn_array_ptr_size (&dest->bridges)); /* We flattened the color graph, so this must never happen. */

				api_xrefs [api_index].src_scc_index = src->api_index;
				api_xrefs [api_index].dst_scc_index = dest->api_index;
				++api_index;
			}
		}
	}

	g_assert (xref_count == api_index);
	xref_setup_time = step_timer (&curtime);

#if defined (DUMP_GRAPH)
	printf ("---xrefs:\n");
	for (i = 0; i < xref_count; ++i)
		printf ("\t%d -> %d\n", api_xrefs [i].src_scc_index, api_xrefs [i].dst_scc_index);
#endif

	//FIXME move half of the cleanup to before the bridge callback?
	bridge_processor->num_sccs = num_colors_with_bridges;
	bridge_processor->api_sccs = api_sccs;
	bridge_processor->num_xrefs = xref_count;
	bridge_processor->api_xrefs = api_xrefs;
}

static void
processing_after_callback (int generation)
{
	gint64 curtime;
	int bridge_count = dyn_array_ptr_size (&registered_bridges);
	int object_count = object_data_count;
	int color_count = color_data_count;
	int scc_count = num_colors_with_bridges;

	SGEN_TV_GETTIME (curtime);

	/* cleanup */
	cleanup ();

	cleanup_time = step_timer (&curtime);

	mono_trace (G_LOG_LEVEL_INFO, MONO_TRACE_GC, "GC_TAR_BRIDGE bridges %d objects %d colors %d ignored %d sccs %d xref %d cache %d/%d setup %.2fms tarjan %.2fms scc-setup %.2fms gather-xref %.2fms xref-setup %.2fms cleanup %.2fms",
		bridge_count, object_count, color_count,
		ignored_objects, scc_count, xref_count,
		cache_hits, cache_misses,
		setup_time / 10000.0f,
		tarjan_time / 10000.0f,
		scc_setup_time / 10000.0f,
		gather_xref_time / 10000.0f,
		xref_setup_time / 10000.0f,
		cleanup_time / 10000.0f);

	cache_hits = cache_misses = 0;
	ignored_objects = 0;
	bridge_processing_in_progress = FALSE;
}

static void
describe_pointer (MonoObject *obj)
{
	// HashEntry *entry;
	int i;

	for (i = 0; i < dyn_array_ptr_size (&registered_bridges); ++i) {
		if (obj == dyn_array_ptr_get (&registered_bridges, i)) {
			printf ("Pointer is a registered bridge object.\n");
			break;
		}
	}

	// entry = sgen_hash_table_lookup (&hash_table, obj);
	// if (!entry)
	// 	return;
	//
	// printf ("Bridge hash table entry %p:\n", entry);
	// printf ("  is bridge: %d\n", (int)entry->is_bridge);
	// printf ("  is visited: %d\n", (int)entry->is_visited);
}

void
sgen_tarjan_bridge_init (SgenBridgeProcessor *collector)
{
	collector->reset_data = reset_data;
	collector->processing_stw_step = processing_stw_step;
	collector->processing_build_callback_data = processing_build_callback_data;
	collector->processing_after_callback = processing_after_callback;
	collector->class_kind = class_kind;
	collector->register_finalized_object = register_finalized_object;
	collector->describe_pointer = describe_pointer;
	collector->enable_accounting = enable_accounting;
	// collector->set_dump_prefix = set_dump_prefix;

	sgen_register_fixed_internal_mem_type (INTERNAL_MEM_TARJAN_OBJ_BUCKET, BUCKET_SIZE);
	g_assert (sizeof (ObjectBucket) <= BUCKET_SIZE);
	g_assert (sizeof (ColorBucket) <= BUCKET_SIZE);
	bridge_processor = collector;
}

#endif