Zend/zend_gc.c

/*
   +----------------------------------------------------------------------+
   | Zend Engine                                                          |
   +----------------------------------------------------------------------+
   | Copyright (c) 1998-2017 Zend Technologies Ltd. (http://www.zend.com) |
   +----------------------------------------------------------------------+
   | This source file is subject to version 2.00 of the Zend license,     |
   | that is bundled with this package in the file LICENSE, and is        |
   | available through the world-wide-web at the following url:           |
   | http://www.zend.com/license/2_00.txt.                                |
   | If you did not receive a copy of the Zend license and are unable to  |
   | obtain it through the world-wide-web, please send a note to          |
   | license@zend.com so we can mail you a copy immediately.              |
   +----------------------------------------------------------------------+
   | Authors: David Wang <planetbeing@gmail.com>                          |
   |          Dmitry Stogov <dmitry@zend.com>                             |
   +----------------------------------------------------------------------+
*/

/* $Id$ */


/**
 * zend_gc_collect_cycles
 * ======================
 *
 * Colors and its meaning
 * ----------------------
 *
 * BLACK  (GC_BLACK)   - In use or free.
 * GREY   (GC_GREY)    - Possible member of cycle.
 * WHITE  (GC_WHITE)   - Member of garbage cycle.
 * PURPLE (GC_PURPLE)  - Possible root of cycle.
 *
 * Colors described in the paper but not used
 * ------------------------------------------
 *
 * GREEN - Acyclic
 * RED   - Candidate cycle underogin
 * ORANGE - Candidate cycle awaiting epoch boundary.
 *
 *
 * Flow
 * =====
 *
 * The garbage collect cycle starts from 'gc_mark_roots', which traverses the
 * possible roots, and calls mark_grey for roots are marked purple with
 * depth-first traverse.
 *
 * After all possible roots are traversed and marked,
 * gc_scan_roots will be called, and each root will be called with
 * gc_scan(root->ref)
 *
 * gc_scan checkes the colors of possible members.
 *
 * If the node is marked as grey and the refcount > 0
 *    gc_scan_black will be called on that node to scan it's subgraph.
 * otherwise (refcount == 0), it marks the node white.
 *
 * A node MAY be added to possbile roots when ZEND_UNSET_VAR happens or
 * zend_assign_to_variable is called only when possible garbage node is
 * produced.
 * gc_possible_root() will be called to add the nodes to possible roots.
 *
 *
 * For objects, we call their get_gc handler (by default 'zend_std_get_gc') to
 * get the object properties to scan.
 *
 *
 * @see http://researcher.watson.ibm.com/researcher/files/us-bacon/Bacon01Concurrent.pdf
 */
#include "zend.h"
#include "zend_API.h"

/* one (0) is reserved */
#define GC_ROOT_BUFFER_MAX_ENTRIES 10001

#define GC_HAS_DESTRUCTORS  (1<<0)

#ifndef ZEND_GC_DEBUG
# define ZEND_GC_DEBUG 0
#endif

#ifdef ZTS
ZEND_API int gc_globals_id;
#else
ZEND_API zend_gc_globals gc_globals;
#endif

ZEND_API int (*gc_collect_cycles)(void);

#if ZEND_GC_DEBUG > 1
# define GC_TRACE(format, ...) fprintf(stderr, format "\n", ##__VA_ARGS__);
# define GC_TRACE_REF(ref, format, ...) \
	do { \
		gc_trace_ref((zend_refcounted *) ref); \
		fprintf(stderr, format "\n", ##__VA_ARGS__); \
	} while (0)
# define GC_TRACE_SET_COLOR(ref, color) \
	GC_TRACE_REF(ref, "->%s", gc_color_name(color))
#else
# define GC_TRACE_REF(ref, format, ...)
# define GC_TRACE_SET_COLOR(ref, new_color)
# define GC_TRACE(str)
#endif

#define GC_REF_SET_ADDRESS(ref, a) \
	GC_INFO_SET_ADDRESS(GC_INFO(ref), a)
#define GC_REF_GET_COLOR(ref) \
	GC_INFO_GET_COLOR(GC_INFO(ref))
#define GC_REF_SET_COLOR(ref, c) \
	do { GC_TRACE_SET_COLOR(ref, c); GC_INFO_SET_COLOR(GC_INFO(ref), c); } while (0)
#define GC_REF_SET_BLACK(ref) \
	do { GC_TRACE_SET_COLOR(ref, GC_BLACK); GC_INFO_SET_BLACK(GC_INFO(ref)); } while (0)
#define GC_REF_SET_PURPLE(ref) \
	do { GC_TRACE_SET_COLOR(ref, GC_PURPLE); GC_INFO_SET_PURPLE(GC_INFO(ref)); } while (0)

#if ZEND_GC_DEBUG > 1
static const char *gc_color_name(uint32_t color) {
	switch (color) {
		case GC_BLACK: return "black";
		case GC_WHITE: return "white";
		case GC_GREY: return "grey";
		case GC_PURPLE: return "purple";
		default: return "unknown";
	}
}
static void gc_trace_ref(zend_refcounted *ref) {
	if (GC_TYPE(ref) == IS_OBJECT) {
		zend_object *obj = (zend_object *) ref;
		fprintf(stderr, "[%p] rc=%d addr=%d %s object(%s)#%d ",
			ref, GC_REFCOUNT(ref), GC_ADDRESS(GC_INFO(ref)),
			gc_color_name(GC_REF_GET_COLOR(ref)),
			obj->ce->name->val, obj->handle);
	} else if (GC_TYPE(ref) == IS_ARRAY) {
		zend_array *arr = (zend_array *) ref;
		fprintf(stderr, "[%p] rc=%d addr=%d %s array(%d) ",
			ref, GC_REFCOUNT(ref), GC_ADDRESS(GC_INFO(ref)),
			gc_color_name(GC_REF_GET_COLOR(ref)),
			zend_hash_num_elements(arr));
	} else {
		fprintf(stderr, "[%p] rc=%d addr=%d %s %s ",
			ref, GC_REFCOUNT(ref), GC_ADDRESS(GC_INFO(ref)),
			gc_color_name(GC_REF_GET_COLOR(ref)),
			zend_get_type_by_const(GC_TYPE(ref)));
	}
}
#endif

static zend_always_inline void gc_remove_from_roots(gc_root_buffer *root)
{
	root->next->prev = root->prev;
	root->prev->next = root->next;
	root->prev = GC_G(unused);
	GC_G(unused) = root;
	GC_BENCH_DEC(root_buf_length);
}

static zend_always_inline void gc_remove_from_additional_roots(gc_root_buffer *root)
{
	root->next->prev = root->prev;
	root->prev->next = root->next;
}

static void root_buffer_dtor(zend_gc_globals *gc_globals)
{
	if (gc_globals->buf) {
		free(gc_globals->buf);
		gc_globals->buf = NULL;
	}
}

static void gc_globals_ctor_ex(zend_gc_globals *gc_globals)
{
	gc_globals->gc_enabled = 0;
	gc_globals->gc_active = 0;

	gc_globals->buf = NULL;

	gc_globals->roots.next = &gc_globals->roots;
	gc_globals->roots.prev = &gc_globals->roots;
	gc_globals->unused = NULL;
	gc_globals->next_to_free = NULL;

	gc_globals->to_free.next = &gc_globals->to_free;
	gc_globals->to_free.prev = &gc_globals->to_free;

	gc_globals->gc_runs = 0;
	gc_globals->collected = 0;

	gc_globals->additional_buffer = NULL;

#if GC_BENCH
	gc_globals->root_buf_length = 0;
	gc_globals->root_buf_peak = 0;
	gc_globals->zval_possible_root = 0;
	gc_globals->zval_buffered = 0;
	gc_globals->zval_remove_from_buffer = 0;
	gc_globals->zval_marked_grey = 0;
#endif
}

ZEND_API void gc_globals_ctor(void)
{
#ifdef ZTS
	ts_allocate_id(&gc_globals_id, sizeof(zend_gc_globals), (ts_allocate_ctor) gc_globals_ctor_ex, (ts_allocate_dtor) root_buffer_dtor);
#else
	gc_globals_ctor_ex(&gc_globals);
#endif
}

ZEND_API void gc_globals_dtor(void)
{
#ifndef ZTS
	root_buffer_dtor(&gc_globals);
#endif
}

ZEND_API void gc_reset(void)
{
	GC_G(gc_runs) = 0;
	GC_G(collected) = 0;
	GC_G(gc_full) = 0;

#if GC_BENCH
	GC_G(root_buf_length) = 0;
	GC_G(root_buf_peak) = 0;
	GC_G(zval_possible_root) = 0;
	GC_G(zval_buffered) = 0;
	GC_G(zval_remove_from_buffer) = 0;
	GC_G(zval_marked_grey) = 0;
#endif

	GC_G(roots).next = &GC_G(roots);
	GC_G(roots).prev = &GC_G(roots);

	GC_G(to_free).next = &GC_G(to_free);
	GC_G(to_free).prev = &GC_G(to_free);

	if (GC_G(buf)) {
		GC_G(unused) = NULL;
		GC_G(first_unused) = GC_G(buf) + 1;
	} else {
		GC_G(unused) = NULL;
		GC_G(first_unused) = NULL;
		GC_G(last_unused) = NULL;
	}

	GC_G(additional_buffer) = NULL;
}

ZEND_API void gc_init(void)
{
	if (GC_G(buf) == NULL && GC_G(gc_enabled)) {
		GC_G(buf) = (gc_root_buffer*) malloc(sizeof(gc_root_buffer) * GC_ROOT_BUFFER_MAX_ENTRIES);
		GC_G(last_unused) = &GC_G(buf)[GC_ROOT_BUFFER_MAX_ENTRIES];
		gc_reset();
	}
}

ZEND_API void ZEND_FASTCALL gc_possible_root(zend_refcounted *ref)
{
	gc_root_buffer *newRoot;

	if (UNEXPECTED(CG(unclean_shutdown)) || UNEXPECTED(GC_G(gc_active))) {
		return;
	}

	ZEND_ASSERT(GC_TYPE(ref) == IS_ARRAY || GC_TYPE(ref) == IS_OBJECT);
	ZEND_ASSERT(EXPECTED(GC_REF_GET_COLOR(ref) == GC_BLACK));
	ZEND_ASSERT(!GC_ADDRESS(GC_INFO(ref)));

	GC_BENCH_INC(zval_possible_root);

	newRoot = GC_G(unused);
	if (newRoot) {
		GC_G(unused) = newRoot->prev;
	} else if (GC_G(first_unused) != GC_G(last_unused)) {
		newRoot = GC_G(first_unused);
		GC_G(first_unused)++;
	} else {
		if (!GC_G(gc_enabled)) {
			return;
		}
		GC_REFCOUNT(ref)++;
		gc_collect_cycles();
		GC_REFCOUNT(ref)--;
		if (UNEXPECTED(GC_REFCOUNT(ref)) == 0) {
			zval_dtor_func(ref);
			return;
		}
		if (UNEXPECTED(GC_INFO(ref))) {
			return;
		}
		newRoot = GC_G(unused);
		if (!newRoot) {
#if ZEND_GC_DEBUG
			if (!GC_G(gc_full)) {
				fprintf(stderr, "GC: no space to record new root candidate\n");
				GC_G(gc_full) = 1;
			}
#endif
			return;
		}
		GC_G(unused) = newRoot->prev;
	}

	GC_TRACE_SET_COLOR(ref, GC_PURPLE);
	GC_INFO(ref) = (newRoot - GC_G(buf)) | GC_PURPLE;
	newRoot->ref = ref;

	newRoot->next = GC_G(roots).next;
	newRoot->prev = &GC_G(roots);
	GC_G(roots).next->prev = newRoot;
	GC_G(roots).next = newRoot;

	GC_BENCH_INC(zval_buffered);
	GC_BENCH_INC(root_buf_length);
	GC_BENCH_PEAK(root_buf_peak, root_buf_length);
}

static zend_always_inline gc_root_buffer* gc_find_additional_buffer(zend_refcounted *ref)
{
	gc_additional_buffer *additional_buffer = GC_G(additional_buffer);

	/* We have to check each additional_buffer to find which one holds the ref */
	while (additional_buffer) {
		uint32_t idx = GC_ADDRESS(GC_INFO(ref)) - GC_ROOT_BUFFER_MAX_ENTRIES;
		if (idx < additional_buffer->used) {
			gc_root_buffer *root = additional_buffer->buf + idx;
			if (root->ref == ref) {
				return root;
			}
		}
		additional_buffer = additional_buffer->next;
	}

	ZEND_ASSERT(0);
	return NULL;
}

ZEND_API void ZEND_FASTCALL gc_remove_from_buffer(zend_refcounted *ref)
{
	gc_root_buffer *root;

	ZEND_ASSERT(GC_ADDRESS(GC_INFO(ref)));

	GC_BENCH_INC(zval_remove_from_buffer);

	if (EXPECTED(GC_ADDRESS(GC_INFO(ref)) < GC_ROOT_BUFFER_MAX_ENTRIES)) {
		root = GC_G(buf) + GC_ADDRESS(GC_INFO(ref));
		gc_remove_from_roots(root);
	} else {
		root = gc_find_additional_buffer(ref);
		gc_remove_from_additional_roots(root);
	}
	if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
		GC_TRACE_SET_COLOR(ref, GC_PURPLE);
	}
	GC_INFO(ref) = 0;

	/* updete next root that is going to be freed */
	if (GC_G(next_to_free) == root) {
		GC_G(next_to_free) = root->next;
	}
}

static void gc_scan_black(zend_refcounted *ref)
{
	HashTable *ht;
	Bucket *p, *end;
	zval *zv;

tail_call:
	ht = NULL;
	GC_REF_SET_BLACK(ref);

	if (GC_TYPE(ref) == IS_OBJECT) {
		zend_object_get_gc_t get_gc;
		zend_object *obj = (zend_object*)ref;

		ZEND_ASSERT(EG(objects_store).object_buckets != NULL);
		if (EXPECTED(!(GC_FLAGS(ref) & IS_OBJ_FREE_CALLED) &&
		             IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
		             (get_gc = obj->handlers->get_gc) != NULL)) {
			int n;
			zval *zv, *end;
			zval tmp;

			ZVAL_OBJ(&tmp, obj);
			ht = get_gc(&tmp, &zv, &n);
			end = zv + n;
			if (EXPECTED(!ht)) {
				if (!n) return;
				while (!Z_REFCOUNTED_P(--end)) {
					if (zv == end) return;
				}
			}
			while (zv != end) {
				if (Z_REFCOUNTED_P(zv)) {
					ref = Z_COUNTED_P(zv);
					GC_REFCOUNT(ref)++;
					if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
						gc_scan_black(ref);
					}
				}
				zv++;
			}
			if (EXPECTED(!ht)) {
				ref = Z_COUNTED_P(zv);
				GC_REFCOUNT(ref)++;
				if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
					goto tail_call;
				}
				return;
			}
		} else {
			return;
		}
	} else if (GC_TYPE(ref) == IS_ARRAY) {
		if ((zend_array*)ref != &EG(symbol_table)) {
			ht = (zend_array*)ref;
		} else {
			return;
		}
	} else if (GC_TYPE(ref) == IS_REFERENCE) {
		if (Z_REFCOUNTED(((zend_reference*)ref)->val)) {
			ref = Z_COUNTED(((zend_reference*)ref)->val);
			GC_REFCOUNT(ref)++;
			if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
				goto tail_call;
			}
		}
		return;
	} else {
		return;
	}

	if (!ht->nNumUsed) return;
	p = ht->arData;
	end = p + ht->nNumUsed;
	while (1) {
		end--;
		zv = &end->val;
		if (Z_TYPE_P(zv) == IS_INDIRECT) {
			zv = Z_INDIRECT_P(zv);
		}
		if (Z_REFCOUNTED_P(zv)) {
			break;
		}
		if (p == end) return;
	}
	while (p != end) {
		zv = &p->val;
		if (Z_TYPE_P(zv) == IS_INDIRECT) {
			zv = Z_INDIRECT_P(zv);
		}
		if (Z_REFCOUNTED_P(zv)) {
			ref = Z_COUNTED_P(zv);
			GC_REFCOUNT(ref)++;
			if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
				gc_scan_black(ref);
			}
		}
		p++;
	}
	zv = &p->val;
	if (Z_TYPE_P(zv) == IS_INDIRECT) {
		zv = Z_INDIRECT_P(zv);
	}
	ref = Z_COUNTED_P(zv);
	GC_REFCOUNT(ref)++;
	if (GC_REF_GET_COLOR(ref) != GC_BLACK) {
		goto tail_call;
	}
}

static void gc_mark_grey(zend_refcounted *ref)
{
    HashTable *ht;
	Bucket *p, *end;
	zval *zv;

tail_call:
	if (GC_REF_GET_COLOR(ref) != GC_GREY) {
		ht = NULL;
		GC_BENCH_INC(zval_marked_grey);
		GC_REF_SET_COLOR(ref, GC_GREY);

		if (GC_TYPE(ref) == IS_OBJECT) {
			zend_object_get_gc_t get_gc;
			zend_object *obj = (zend_object*)ref;

			ZEND_ASSERT(EG(objects_store).object_buckets != NULL);
			if (EXPECTED(!(GC_FLAGS(ref) & IS_OBJ_FREE_CALLED) &&
			             IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
		                 (get_gc = obj->handlers->get_gc) != NULL)) {
				int n;
				zval *zv, *end;
				zval tmp;

				ZVAL_OBJ(&tmp, obj);
				ht = get_gc(&tmp, &zv, &n);
				end = zv + n;
				if (EXPECTED(!ht)) {
					if (!n) return;
					while (!Z_REFCOUNTED_P(--end)) {
						if (zv == end) return;
					}
				}
				while (zv != end) {
					if (Z_REFCOUNTED_P(zv)) {
						ref = Z_COUNTED_P(zv);
						GC_REFCOUNT(ref)--;
						gc_mark_grey(ref);
					}
					zv++;
				}
				if (EXPECTED(!ht)) {
					ref = Z_COUNTED_P(zv);
					GC_REFCOUNT(ref)--;
					goto tail_call;
				}
			} else {
				return;
			}
		} else if (GC_TYPE(ref) == IS_ARRAY) {
			if (((zend_array*)ref) == &EG(symbol_table)) {
				GC_REF_SET_BLACK(ref);
				return;
			} else {
				ht = (zend_array*)ref;
			}
		} else if (GC_TYPE(ref) == IS_REFERENCE) {
			if (Z_REFCOUNTED(((zend_reference*)ref)->val)) {
				ref = Z_COUNTED(((zend_reference*)ref)->val);
				GC_REFCOUNT(ref)--;
				goto tail_call;
			}
			return;
		} else {
			return;
		}

		if (!ht->nNumUsed) return;
		p = ht->arData;
		end = p + ht->nNumUsed;
		while (1) {
			end--;
			zv = &end->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				break;
			}
			if (p == end) return;
		}
		while (p != end) {
			zv = &p->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				ref = Z_COUNTED_P(zv);
				GC_REFCOUNT(ref)--;
				gc_mark_grey(ref);
			}
			p++;
		}
		zv = &p->val;
		if (Z_TYPE_P(zv) == IS_INDIRECT) {
			zv = Z_INDIRECT_P(zv);
		}
		ref = Z_COUNTED_P(zv);
		GC_REFCOUNT(ref)--;
		goto tail_call;
	}
}

static void gc_mark_roots(void)
{
	gc_root_buffer *current = GC_G(roots).next;

	while (current != &GC_G(roots)) {
		if (GC_REF_GET_COLOR(current->ref) == GC_PURPLE) {
			gc_mark_grey(current->ref);
		}
		current = current->next;
	}
}

static void gc_scan(zend_refcounted *ref)
{
    HashTable *ht;
	Bucket *p, *end;
	zval *zv;

tail_call:
	if (GC_REF_GET_COLOR(ref) == GC_GREY) {
		if (GC_REFCOUNT(ref) > 0) {
			gc_scan_black(ref);
		} else {
			GC_REF_SET_COLOR(ref, GC_WHITE);
			if (GC_TYPE(ref) == IS_OBJECT) {
				zend_object_get_gc_t get_gc;
				zend_object *obj = (zend_object*)ref;

				ZEND_ASSERT(EG(objects_store).object_buckets != NULL);
				if (EXPECTED(!(GC_FLAGS(ref) & IS_OBJ_FREE_CALLED) &&
				             IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
				             (get_gc = obj->handlers->get_gc) != NULL)) {
					int n;
					zval *zv, *end;
					zval tmp;

					ZVAL_OBJ(&tmp, obj);
					ht = get_gc(&tmp, &zv, &n);
					end = zv + n;
					if (EXPECTED(!ht)) {
						if (!n) return;
						while (!Z_REFCOUNTED_P(--end)) {
							if (zv == end) return;
						}
					}
					while (zv != end) {
						if (Z_REFCOUNTED_P(zv)) {
							ref = Z_COUNTED_P(zv);
							gc_scan(ref);
						}
						zv++;
					}
					if (EXPECTED(!ht)) {
						ref = Z_COUNTED_P(zv);
						goto tail_call;
					}
				} else {
					return;
				}
			} else if (GC_TYPE(ref) == IS_ARRAY) {
				if ((zend_array*)ref == &EG(symbol_table)) {
					GC_REF_SET_BLACK(ref);
					return;
				} else {
					ht = (zend_array*)ref;
				}
			} else if (GC_TYPE(ref) == IS_REFERENCE) {
				if (Z_REFCOUNTED(((zend_reference*)ref)->val)) {
					ref = Z_COUNTED(((zend_reference*)ref)->val);
					goto tail_call;
				}
				return;
			} else {
				return;
			}

			if (!ht->nNumUsed) return;
			p = ht->arData;
			end = p + ht->nNumUsed;
			while (1) {
				end--;
				zv = &end->val;
				if (Z_TYPE_P(zv) == IS_INDIRECT) {
					zv = Z_INDIRECT_P(zv);
				}
				if (Z_REFCOUNTED_P(zv)) {
					break;
				}
				if (p == end) return;
			}
			while (p != end) {
				zv = &p->val;
				if (Z_TYPE_P(zv) == IS_INDIRECT) {
					zv = Z_INDIRECT_P(zv);
				}
				if (Z_REFCOUNTED_P(zv)) {
					ref = Z_COUNTED_P(zv);
					gc_scan(ref);
				}
				p++;
			}
			zv = &p->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			ref = Z_COUNTED_P(zv);
			goto tail_call;
		}
	}
}

static void gc_scan_roots(void)
{
	gc_root_buffer *current = GC_G(roots).next;

	while (current != &GC_G(roots)) {
		gc_scan(current->ref);
		current = current->next;
	}
}

static void gc_add_garbage(zend_refcounted *ref)
{
	gc_root_buffer *buf = GC_G(unused);

	if (buf) {
		GC_G(unused) = buf->prev;
#if 1
		/* optimization: color is already GC_BLACK (0) */
		GC_INFO(ref) = buf - GC_G(buf);
#else
		GC_REF_SET_ADDRESS(ref, buf - GC_G(buf));
#endif
	} else if (GC_G(first_unused) != GC_G(last_unused)) {
		buf = GC_G(first_unused);
		GC_G(first_unused)++;
#if 1
		/* optimization: color is already GC_BLACK (0) */
		GC_INFO(ref) = buf - GC_G(buf);
#else
		GC_REF_SET_ADDRESS(ref, buf - GC_G(buf));
#endif
	} else {
		/* If we don't have free slots in the buffer, allocate a new one and
		 * set it's address above GC_ROOT_BUFFER_MAX_ENTRIES that have special
		 * meaning.
		 */
		if (!GC_G(additional_buffer) || GC_G(additional_buffer)->used == GC_NUM_ADDITIONAL_ENTRIES) {
			gc_additional_buffer *new_buffer = emalloc(sizeof(gc_additional_buffer));
			new_buffer->used = 0;
			new_buffer->next = GC_G(additional_buffer);
			GC_G(additional_buffer) = new_buffer;
		}
		buf = GC_G(additional_buffer)->buf + GC_G(additional_buffer)->used;
#if 1
		/* optimization: color is already GC_BLACK (0) */
		GC_INFO(ref) = GC_ROOT_BUFFER_MAX_ENTRIES + GC_G(additional_buffer)->used;
#else
		GC_REF_SET_ADDRESS(ref, GC_ROOT_BUFFER_MAX_ENTRIES) + GC_G(additional_buffer)->used;
#endif
		GC_G(additional_buffer)->used++;
	}
	if (buf) {
		buf->ref = ref;
		buf->next = GC_G(roots).next;
		buf->prev = &GC_G(roots);
		GC_G(roots).next->prev = buf;
		GC_G(roots).next = buf;
	}
}

static int gc_collect_white(zend_refcounted *ref, uint32_t *flags)
{
	int count = 0;
	HashTable *ht;
	Bucket *p, *end;
	zval *zv;

tail_call:
	if (GC_REF_GET_COLOR(ref) == GC_WHITE) {
		ht = NULL;
		GC_REF_SET_BLACK(ref);

		/* don't count references for compatibility ??? */
		if (GC_TYPE(ref) != IS_REFERENCE) {
			count++;
		}

		if (GC_TYPE(ref) == IS_OBJECT) {
			zend_object_get_gc_t get_gc;
			zend_object *obj = (zend_object*)ref;

			ZEND_ASSERT(EG(objects_store).object_buckets != NULL);
			if (EXPECTED(!(GC_FLAGS(ref) & IS_OBJ_FREE_CALLED) &&
			             IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
			             (get_gc = obj->handlers->get_gc) != NULL)) {
				int n;
				zval *zv, *end;
				zval tmp;

#if 1
				/* optimization: color is GC_BLACK (0) */
				if (!GC_INFO(ref)) {
#else
				if (!GC_ADDRESS(GC_INFO(ref))) {
#endif
					gc_add_garbage(ref);
				}
				if (obj->handlers->dtor_obj &&
				    ((obj->handlers->dtor_obj != zend_objects_destroy_object) ||
				     (obj->ce->destructor != NULL))) {
					*flags |= GC_HAS_DESTRUCTORS;
				}
				ZVAL_OBJ(&tmp, obj);
				ht = get_gc(&tmp, &zv, &n);
				end = zv + n;
				if (EXPECTED(!ht)) {
					if (!n) return count;
					while (!Z_REFCOUNTED_P(--end)) {
						/* count non-refcounted for compatibility ??? */
						if (Z_TYPE_P(zv) != IS_UNDEF) {
							count++;
						}
						if (zv == end) return count;
					}
				}
				while (zv != end) {
					if (Z_REFCOUNTED_P(zv)) {
						ref = Z_COUNTED_P(zv);
						GC_REFCOUNT(ref)++;
						count += gc_collect_white(ref, flags);
					/* count non-refcounted for compatibility ??? */
					} else if (Z_TYPE_P(zv) != IS_UNDEF) {
						count++;
					}
					zv++;
				}
				if (EXPECTED(!ht)) {
					ref = Z_COUNTED_P(zv);
					GC_REFCOUNT(ref)++;
					goto tail_call;
				}
			} else {
				return count;
			}
		} else if (GC_TYPE(ref) == IS_ARRAY) {
#if 1
				/* optimization: color is GC_BLACK (0) */
				if (!GC_INFO(ref)) {
#else
				if (!GC_ADDRESS(GC_INFO(ref))) {
#endif
				gc_add_garbage(ref);
			}
			ht = (zend_array*)ref;
		} else if (GC_TYPE(ref) == IS_REFERENCE) {
			if (Z_REFCOUNTED(((zend_reference*)ref)->val)) {
				ref = Z_COUNTED(((zend_reference*)ref)->val);
				GC_REFCOUNT(ref)++;
				goto tail_call;
			}
			return count;
		} else {
			return count;
		}

		if (!ht->nNumUsed) return count;
		p = ht->arData;
		end = p + ht->nNumUsed;
		while (1) {
			end--;
			zv = &end->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				break;
			}
			/* count non-refcounted for compatibility ??? */
			if (Z_TYPE_P(zv) != IS_UNDEF) {
				count++;
			}
			if (p == end) return count;
		}
		while (p != end) {
			zv = &p->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				ref = Z_COUNTED_P(zv);
				GC_REFCOUNT(ref)++;
				count += gc_collect_white(ref, flags);
				/* count non-refcounted for compatibility ??? */
			} else if (Z_TYPE_P(zv) != IS_UNDEF) {
				count++;
			}
			p++;
		}
		zv = &p->val;
		if (Z_TYPE_P(zv) == IS_INDIRECT) {
			zv = Z_INDIRECT_P(zv);
		}
		ref = Z_COUNTED_P(zv);
		GC_REFCOUNT(ref)++;
		goto tail_call;
	}
	return count;
}

static int gc_collect_roots(uint32_t *flags)
{
	int count = 0;
	gc_root_buffer *current = GC_G(roots).next;

	/* remove non-garbage from the list */
	while (current != &GC_G(roots)) {
		gc_root_buffer *next = current->next;
		if (GC_REF_GET_COLOR(current->ref) == GC_BLACK) {
			if (EXPECTED(GC_ADDRESS(GC_INFO(current->ref)) < GC_ROOT_BUFFER_MAX_ENTRIES)) {
				gc_remove_from_roots(current);
			} else {
				gc_remove_from_additional_roots(current);
			}
			GC_INFO(current->ref) = 0; /* reset GC_ADDRESS() and keep GC_BLACK */
		}
		current = next;
	}

	current = GC_G(roots).next;
	while (current != &GC_G(roots)) {
		if (GC_REF_GET_COLOR(current->ref) == GC_WHITE) {
			count += gc_collect_white(current->ref, flags);
		}
		current = current->next;
	}

	/* relink remaining roots into list to free */
	if (GC_G(roots).next != &GC_G(roots)) {
		if (GC_G(to_free).next == &GC_G(to_free)) {
			/* move roots into list to free */
			GC_G(to_free).next = GC_G(roots).next;
			GC_G(to_free).prev = GC_G(roots).prev;
			GC_G(to_free).next->prev = &GC_G(to_free);
			GC_G(to_free).prev->next = &GC_G(to_free);
		} else {
			/* add roots into list to free */
			GC_G(to_free).prev->next = GC_G(roots).next;
			GC_G(roots).next->prev = GC_G(to_free).prev;
			GC_G(roots).prev->next = &GC_G(to_free);
			GC_G(to_free).prev = GC_G(roots).prev;
		}

		GC_G(roots).next = &GC_G(roots);
		GC_G(roots).prev = &GC_G(roots);
	}
	return count;
}

static void gc_remove_nested_data_from_buffer(zend_refcounted *ref, gc_root_buffer *root)
{
	HashTable *ht = NULL;
	Bucket *p, *end;
	zval *zv;

tail_call:
	if (root ||
	    (GC_ADDRESS(GC_INFO(ref)) != 0 &&
	     GC_REF_GET_COLOR(ref) == GC_BLACK)) {
		GC_TRACE_REF(ref, "removing from buffer");
		if (root) {
			if (EXPECTED(GC_ADDRESS(GC_INFO(root->ref)) < GC_ROOT_BUFFER_MAX_ENTRIES)) {
				gc_remove_from_roots(root);
			} else {
				gc_remove_from_additional_roots(root);
			}
			GC_INFO(ref) = 0;
			root = NULL;
		} else {
			GC_REMOVE_FROM_BUFFER(ref);
		}

		if (GC_TYPE(ref) == IS_OBJECT) {
			zend_object_get_gc_t get_gc;
			zend_object *obj = (zend_object*)ref;

			ZEND_ASSERT(EG(objects_store).object_buckets != NULL);
			if (EXPECTED(!(GC_FLAGS(ref) & IS_OBJ_FREE_CALLED) &&
			             IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
		                 (get_gc = obj->handlers->get_gc) != NULL)) {
				int n;
				zval *zv, *end;
				zval tmp;

				ZVAL_OBJ(&tmp, obj);
				ht = get_gc(&tmp, &zv, &n);
				end = zv + n;
				if (EXPECTED(!ht)) {
					if (!n) return;
					while (!Z_REFCOUNTED_P(--end)) {
						if (zv == end) return;
					}
				}
				while (zv != end) {
					if (Z_REFCOUNTED_P(zv)) {
						ref = Z_COUNTED_P(zv);
						gc_remove_nested_data_from_buffer(ref, NULL);
					}
					zv++;
				}
				if (EXPECTED(!ht)) {
					ref = Z_COUNTED_P(zv);
					goto tail_call;
				}
			} else {
				return;
			}
		} else if (GC_TYPE(ref) == IS_ARRAY) {
			ht = (zend_array*)ref;
		} else if (GC_TYPE(ref) == IS_REFERENCE) {
			if (Z_REFCOUNTED(((zend_reference*)ref)->val)) {
				ref = Z_COUNTED(((zend_reference*)ref)->val);
				goto tail_call;
			}
			return;
		} else {
			return;
		}

		if (!ht->nNumUsed) return;
		p = ht->arData;
		end = p + ht->nNumUsed;
		while (1) {
			end--;
			zv = &end->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				break;
			}
			if (p == end) return;
		}
		while (p != end) {
			zv = &p->val;
			if (Z_TYPE_P(zv) == IS_INDIRECT) {
				zv = Z_INDIRECT_P(zv);
			}
			if (Z_REFCOUNTED_P(zv)) {
				ref = Z_COUNTED_P(zv);
				gc_remove_nested_data_from_buffer(ref, NULL);
			}
			p++;
		}
		zv = &p->val;
		if (Z_TYPE_P(zv) == IS_INDIRECT) {
			zv = Z_INDIRECT_P(zv);
		}
		ref = Z_COUNTED_P(zv);
		goto tail_call;
	}
}

ZEND_API int zend_gc_collect_cycles(void)
{
	int count = 0;

	if (GC_G(roots).next != &GC_G(roots)) {
		gc_root_buffer *current, *next, *orig_next_to_free;
		zend_refcounted *p;
		gc_root_buffer to_free;
		uint32_t gc_flags = 0;
		gc_additional_buffer *additional_buffer_snapshot;
#if ZEND_GC_DEBUG
		zend_bool orig_gc_full;
#endif

		if (GC_G(gc_active)) {
			return 0;
		}

		GC_TRACE("Collecting cycles");
		GC_G(gc_runs)++;
		GC_G(gc_active) = 1;

		GC_TRACE("Marking roots");
		gc_mark_roots();
		GC_TRACE("Scanning roots");
		gc_scan_roots();

#if ZEND_GC_DEBUG
		orig_gc_full = GC_G(gc_full);
		GC_G(gc_full) = 0;
#endif

		GC_TRACE("Collecting roots");
		additional_buffer_snapshot = GC_G(additional_buffer);
		count = gc_collect_roots(&gc_flags);
#if ZEND_GC_DEBUG
		GC_G(gc_full) = orig_gc_full;
#endif
		GC_G(gc_active) = 0;

		if (GC_G(to_free).next == &GC_G(to_free)) {
			/* nothing to free */
			GC_TRACE("Nothing to free");
			return 0;
		}

		/* Copy global to_free list into local list */
		to_free.next = GC_G(to_free).next;
		to_free.prev = GC_G(to_free).prev;
		to_free.next->prev = &to_free;
		to_free.prev->next = &to_free;

		/* Free global list */
		GC_G(to_free).next = &GC_G(to_free);
		GC_G(to_free).prev = &GC_G(to_free);

		orig_next_to_free = GC_G(next_to_free);

#if ZEND_GC_DEBUG
		orig_gc_full = GC_G(gc_full);
		GC_G(gc_full) = 0;
#endif

		if (gc_flags & GC_HAS_DESTRUCTORS) {
			GC_TRACE("Calling destructors");

			/* Remember reference counters before calling destructors */
			current = to_free.next;
			while (current != &to_free) {
				current->refcount = GC_REFCOUNT(current->ref);
				current = current->next;
			}

			/* Call destructors */
			current = to_free.next;
			while (current != &to_free) {
				p = current->ref;
				GC_G(next_to_free) = current->next;
				if (GC_TYPE(p) == IS_OBJECT) {
					zend_object *obj = (zend_object*)p;

					if (IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle]) &&
						!(GC_FLAGS(obj) & IS_OBJ_DESTRUCTOR_CALLED)) {
						GC_TRACE_REF(obj, "calling destructor");
						GC_FLAGS(obj) |= IS_OBJ_DESTRUCTOR_CALLED;
						if (obj->handlers->dtor_obj) {
							GC_REFCOUNT(obj)++;
							obj->handlers->dtor_obj(obj);
							GC_REFCOUNT(obj)--;
						}
					}
				}
				current = GC_G(next_to_free);
			}

			/* Remove values captured in destructors */
			current = to_free.next;
			while (current != &to_free) {
				GC_G(next_to_free) = current->next;
				if (GC_REFCOUNT(current->ref) > current->refcount) {
					gc_remove_nested_data_from_buffer(current->ref, current);
				}
				current = GC_G(next_to_free);
			}
		}

		/* Destroy zvals */
		GC_TRACE("Destroying zvals");
		GC_G(gc_active) = 1;
		current = to_free.next;
		while (current != &to_free) {
			p = current->ref;
			GC_G(next_to_free) = current->next;
			GC_TRACE_REF(p, "destroying");
			if (GC_TYPE(p) == IS_OBJECT) {
				zend_object *obj = (zend_object*)p;

				if (IS_OBJ_VALID(EG(objects_store).object_buckets[obj->handle])) {
					EG(objects_store).object_buckets[obj->handle] = SET_OBJ_INVALID(obj);
					GC_TYPE(obj) = IS_NULL;
					if (!(GC_FLAGS(obj) & IS_OBJ_FREE_CALLED)) {
						GC_FLAGS(obj) |= IS_OBJ_FREE_CALLED;
						if (obj->handlers->free_obj) {
							GC_REFCOUNT(obj)++;
							obj->handlers->free_obj(obj);
							GC_REFCOUNT(obj)--;
						}
					}
					SET_OBJ_BUCKET_NUMBER(EG(objects_store).object_buckets[obj->handle], EG(objects_store).free_list_head);
					EG(objects_store).free_list_head = obj->handle;
					p = current->ref = (zend_refcounted*)(((char*)obj) - obj->handlers->offset);
				}
			} else if (GC_TYPE(p) == IS_ARRAY) {
				zend_array *arr = (zend_array*)p;

				GC_TYPE(arr) = IS_NULL;

				/* GC may destroy arrays with rc>1. This is valid and safe. */
				HT_ALLOW_COW_VIOLATION(arr);

				zend_hash_destroy(arr);
			}
			current = GC_G(next_to_free);
		}

		/* Free objects */
		current = to_free.next;
		while (current != &to_free) {
			next = current->next;
			p = current->ref;
			if (EXPECTED(current >= GC_G(buf) && current < GC_G(buf) + GC_ROOT_BUFFER_MAX_ENTRIES)) {
				current->prev = GC_G(unused);
				GC_G(unused) = current;
			}
			efree(p);
			current = next;
		}

		while (GC_G(additional_buffer) != additional_buffer_snapshot) {
			gc_additional_buffer *next = GC_G(additional_buffer)->next;
			efree(GC_G(additional_buffer));
			GC_G(additional_buffer) = next;
		}

		GC_TRACE("Collection finished");
		GC_G(collected) += count;
		GC_G(next_to_free) = orig_next_to_free;
#if ZEND_GC_DEBUG
		GC_G(gc_full) = orig_gc_full;
#endif
		GC_G(gc_active) = 0;
	}

	return count;
}

/*
 * Local variables:
 * tab-width: 4
 * c-basic-offset: 4
 * indent-tabs-mode: t
 * End:
 *
 * vim:noexpandtab:
 */