text: /*
   * metadata/gc.c: GC icalls.
   *
   * Author: Paolo Molaro <lupus@ximian.com>
   *
   * Copyright 2002-2003 Ximian, Inc (http://www.ximian.com)
   * Copyright 2004-2009 Novell, Inc (http://www.novell.com)
   * Copyright 2012 Xamarin Inc (http://www.xamarin.com)
   */
  
  #include <config.h>
  #include <glib.h>
  #include <string.h>
  
  #include <mono/metadata/gc-internal.h>
  #include <mono/metadata/mono-gc.h>
  #include <mono/metadata/threads.h>
  #include <mono/metadata/tabledefs.h>
  #include <mono/metadata/exception.h>
  #include <mono/metadata/profiler-private.h>
  #include <mono/metadata/domain-internals.h>
  #include <mono/metadata/class-internals.h>
  #include <mono/metadata/metadata-internals.h>
  #include <mono/metadata/mono-mlist.h>
  #include <mono/metadata/threads-types.h>
  #include <mono/metadata/threadpool-ms.h>
  #include <mono/sgen/sgen-conf.h>
  #include <mono/utils/mono-logger-internal.h>
  #include <mono/metadata/gc-internal.h>
  #include <mono/metadata/marshal.h> /* for mono_delegate_free_ftnptr () */
  #include <mono/metadata/attach.h>
  #include <mono/metadata/console-io.h>
  #include <mono/utils/mono-semaphore.h>
  #include <mono/utils/mono-memory-model.h>
  #include <mono/utils/mono-counters.h>
  #include <mono/utils/mono-time.h>
  #include <mono/utils/dtrace.h>
  #include <mono/utils/mono-threads.h>
  #include <mono/utils/atomic.h>
  
  #ifndef HOST_WIN32
  #include <pthread.h>
  #endif
  
  typedef struct DomainFinalizationReq {
  	MonoDomain *domain;
  	HANDLE done_event;
  } DomainFinalizationReq;
  
  static gboolean gc_disabled = FALSE;
  
  static gboolean finalizing_root_domain = FALSE;
  
  gboolean log_finalizers = FALSE;
  gboolean do_not_finalize = FALSE;
  
  #define mono_finalizer_lock() mono_mutex_lock (&finalizer_mutex)
  #define mono_finalizer_unlock() mono_mutex_unlock (&finalizer_mutex)
  static mono_mutex_t finalizer_mutex;
  static mono_mutex_t reference_queue_mutex;
  
  static GSList *domains_to_finalize= NULL;
  static MonoMList *threads_to_finalize = NULL;
  
  static gboolean finalizer_thread_exited;
  /* Uses finalizer_mutex */
  static mono_cond_t exited_cond;
  
  static MonoInternalThread *gc_thread;
  
  static void object_register_finalizer (MonoObject *obj, void (*callback)(void *, void*));
  
  static void mono_gchandle_set_target (guint32 gchandle, MonoObject *obj);
  
  static void reference_queue_proccess_all (void);
  static void mono_reference_queue_cleanup (void);
  static void reference_queue_clear_for_domain (MonoDomain *domain);
  static HANDLE pending_done_event;
  
  static guint32
  guarded_wait (HANDLE handle, guint32 timeout, gboolean alertable)
  {
  	guint32 result;
  
  	MONO_PREPARE_BLOCKING
  	result = WaitForSingleObjectEx (handle, timeout, alertable);
  	MONO_FINISH_BLOCKING
  
  	return result;
  }
  
  static void
  add_thread_to_finalize (MonoInternalThread *thread)
  {
  	mono_finalizer_lock ();
  	if (!threads_to_finalize)
  		MONO_GC_REGISTER_ROOT_SINGLE (threads_to_finalize);
  	threads_to_finalize = mono_mlist_append (threads_to_finalize, (MonoObject*)thread);
  	mono_finalizer_unlock ();
  }
  
  static gboolean suspend_finalizers = FALSE;
  /* 
   * actually, we might want to queue the finalize requests in a separate thread,
   * but we need to be careful about the execution domain of the thread...
   */
  void
  mono_gc_run_finalize (void *obj, void *data)
  {
  	if (do_not_finalize)
  		return;
  
  	MonoObject *exc = NULL;
  	MonoObject *o;
  #ifndef HAVE_SGEN_GC
  	MonoObject *o2;
  #endif
  	MonoMethod* finalizer = NULL;
  	MonoDomain *caller_domain = mono_domain_get ();
  	MonoDomain *domain;
  	RuntimeInvokeFunction runtime_invoke;
  
  	o = (MonoObject*)((char*)obj + GPOINTER_TO_UINT (data));
  
  	if (log_finalizers)
  		g_log ("mono-gc-finalizers", G_LOG_LEVEL_DEBUG, "<%s at %p> Starting finalizer checks.", o->vtable->klass->name, o);
  
  	if (suspend_finalizers)
  		return;
  
  	domain = o->vtable->domain;
  
  #ifndef HAVE_SGEN_GC
  	mono_domain_finalizers_lock (domain);
  
  	o2 = g_hash_table_lookup (domain->finalizable_objects_hash, o);
  
  	mono_domain_finalizers_unlock (domain);
  
  	if (!o2)
  		/* Already finalized somehow */
  		return;
  #endif
  
  	/* make sure the finalizer is not called again if the object is resurrected */
  	object_register_finalizer (obj, NULL);
  
  	if (log_finalizers)
  		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Registered finalizer as processed.", o->vtable->klass->name, o);
  
  	if (o->vtable->klass == mono_defaults.internal_thread_class) {
  		MonoInternalThread *t = (MonoInternalThread*)o;
  
  		if (mono_gc_is_finalizer_internal_thread (t))
  			/* Avoid finalizing ourselves */
  			return;
  
  		if (t->threadpool_thread && finalizing_root_domain) {
  			/* Don't finalize threadpool threads when
  			   shutting down - they're finalized when the
  			   threadpool shuts down. */
  			add_thread_to_finalize (t);
  			return;
  		}
  	}
  
  	if (o->vtable->klass->image == mono_defaults.corlib && !strcmp (o->vtable->klass->name, "DynamicMethod") && finalizing_root_domain) {
  		/*
  		 * These can't be finalized during unloading/shutdown, since that would
  		 * free the native code which can still be referenced by other
  		 * finalizers.
  		 * FIXME: This is not perfect, objects dying at the same time as 
  		 * dynamic methods can still reference them even when !shutdown.
  		 */
  		return;
  	}
  
  	if (mono_runtime_get_no_exec ())
  		return;
  
  	/* speedup later... and use a timeout */
  	/* g_print ("Finalize run on %p %s.%s\n", o, mono_object_class (o)->name_space, mono_object_class (o)->name); */
  
  	/* Use _internal here, since this thread can enter a doomed appdomain */
  	mono_domain_set_internal (mono_object_domain (o));
  
  	/* delegates that have a native function pointer allocated are
  	 * registered for finalization, but they don't have a Finalize
  	 * method, because in most cases it's not needed and it's just a waste.
  	 */
  	if (o->vtable->klass->delegate) {
  		MonoDelegate* del = (MonoDelegate*)o;
  		if (del->delegate_trampoline)
  			mono_delegate_free_ftnptr ((MonoDelegate*)o);
  		mono_domain_set_internal (caller_domain);
  		return;
  	}
  
  	finalizer = mono_class_get_finalizer (o->vtable->klass);
  
  	/* If object has a CCW but has no finalizer, it was only
  	 * registered for finalization in order to free the CCW.
  	 * Else it needs the regular finalizer run.
  	 * FIXME: what to do about ressurection and suppression
  	 * of finalizer on object with CCW.
  	 */
  	if (mono_marshal_free_ccw (o) && !finalizer) {
  		mono_domain_set_internal (caller_domain);
  		return;
  	}
  
  	/* 
  	 * To avoid the locking plus the other overhead of mono_runtime_invoke (),
  	 * create and precompile a wrapper which calls the finalize method using
  	 * a CALLVIRT.
  	 */
  	if (log_finalizers)
  		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Compiling finalizer.", o->vtable->klass->name, o);
  
  	if (!domain->finalize_runtime_invoke) {
  		MonoMethod *invoke = mono_marshal_get_runtime_invoke (mono_class_get_method_from_name_flags (mono_defaults.object_class, "Finalize", 0, 0), TRUE);
  
  		domain->finalize_runtime_invoke = mono_compile_method (invoke);
  	}
  
  	runtime_invoke = domain->finalize_runtime_invoke;
  
  	mono_runtime_class_init (o->vtable);
  
  	if (G_UNLIKELY (MONO_GC_FINALIZE_INVOKE_ENABLED ())) {
  		MONO_GC_FINALIZE_INVOKE ((unsigned long)o, mono_object_get_size (o),
  				o->vtable->klass->name_space, o->vtable->klass->name);
  	}
  
  	if (log_finalizers)
  		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Calling finalizer.", o->vtable->klass->name, o);
  
  	runtime_invoke (o, NULL, &exc, NULL);
  
  	if (log_finalizers)
  		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Returned from finalizer.", o->vtable->klass->name, o);
  
  	if (exc)
  		mono_thread_internal_unhandled_exception (exc);
  
  	mono_domain_set_internal (caller_domain);
  }
  
  void
  mono_gc_finalize_threadpool_threads (void)
  {
  	while (threads_to_finalize) {
  		MonoInternalThread *thread = (MonoInternalThread*) mono_mlist_get_data (threads_to_finalize);
  
  		/* Force finalization of the thread. */
  		thread->threadpool_thread = FALSE;
  		mono_object_register_finalizer ((MonoObject*)thread);
  
  		mono_gc_run_finalize (thread, NULL);
  
  		threads_to_finalize = mono_mlist_next (threads_to_finalize);
  	}
  }
  
  gpointer
  mono_gc_out_of_memory (size_t size)
  {
  	/* 
  	 * we could allocate at program startup some memory that we could release 
  	 * back to the system at this point if we're really low on memory (ie, size is
  	 * lower than the memory we set apart)
  	 */
  	mono_raise_exception (mono_domain_get ()->out_of_memory_ex);
  
  	return NULL;
  }
  
  /*
   * Some of our objects may point to a different address than the address returned by GC_malloc()
   * (because of the GetHashCode hack), but we need to pass the real address to register_finalizer.
   * This also means that in the callback we need to adjust the pointer to get back the real
   * MonoObject*.
   * We also need to be consistent in the use of the GC_debug* variants of malloc and register_finalizer, 
   * since that, too, can cause the underlying pointer to be offset.
   */
  static void
  object_register_finalizer (MonoObject *obj, void (*callback)(void *, void*))
  {
  	MonoDomain *domain;
  
  	if (obj == NULL)
  		mono_raise_exception (mono_get_exception_argument_null ("obj"));
  
  	domain = obj->vtable->domain;
  
  #if HAVE_BOEHM_GC
  	if (mono_domain_is_unloading (domain) && (callback != NULL))
  		/*
  		 * Can't register finalizers in a dying appdomain, since they
  		 * could be invoked after the appdomain has been unloaded.
  		 */
  		return;
  
  	mono_domain_finalizers_lock (domain);
  
  	if (callback)
  		g_hash_table_insert (domain->finalizable_objects_hash, obj, obj);
  	else
  		g_hash_table_remove (domain->finalizable_objects_hash, obj);
  
  	mono_domain_finalizers_unlock (domain);
  
  	mono_gc_register_for_finalization (obj, callback);
  #elif defined(HAVE_SGEN_GC)
  	/*
  	 * If we register finalizers for domains that are unloading we might
  	 * end up running them while or after the domain is being cleared, so
  	 * the objects will not be valid anymore.
  	 */
  	if (!mono_domain_is_unloading (domain))
  		mono_gc_register_for_finalization (obj, callback);
  #endif
  }
  
  /**
   * mono_object_register_finalizer:
   * @obj: object to register
   *
   * Records that object @obj has a finalizer, this will call the
   * Finalize method when the garbage collector disposes the object.
   * 
   */
  void
  mono_object_register_finalizer (MonoObject *obj)
  {
  	/* g_print ("Registered finalizer on %p %s.%s\n", obj, mono_object_class (obj)->name_space, mono_object_class (obj)->name); */
  	object_register_finalizer (obj, mono_gc_run_finalize);
  }
  
  /**
   * mono_domain_finalize:
   * @domain: the domain to finalize
   * @timeout: msects to wait for the finalization to complete, -1 to wait indefinitely
   *
   *  Request finalization of all finalizable objects inside @domain. Wait
   * @timeout msecs for the finalization to complete.
   *
   * Returns: TRUE if succeeded, FALSE if there was a timeout
   */
  
  gboolean
  mono_domain_finalize (MonoDomain *domain, guint32 timeout) 
  {
  	DomainFinalizationReq *req;
  	guint32 res;
  	HANDLE done_event;
  	MonoInternalThread *thread = mono_thread_internal_current ();
  
  #if defined(__native_client__)
  	return FALSE;
  #endif
  
  	if (mono_thread_internal_current () == gc_thread)
  		/* We are called from inside a finalizer, not much we can do here */
  		return FALSE;
  
  	/* 
  	 * No need to create another thread 'cause the finalizer thread
  	 * is still working and will take care of running the finalizers
  	 */ 
  	
  	if (gc_disabled)
  		return TRUE;
  
  	/* We don't support domain finalization without a GC */
  	if (mono_gc_is_null ())
  		return FALSE;
  
  	mono_gc_collect (mono_gc_max_generation ());
  
  	done_event = CreateEvent (NULL, TRUE, FALSE, NULL);
  	if (done_event == NULL) {
  		return FALSE;
  	}
  
  	req = g_new0 (DomainFinalizationReq, 1);
  	req->domain = domain;
  	req->done_event = done_event;
  
  	if (domain == mono_get_root_domain ())
  		finalizing_root_domain = TRUE;
  	
  	mono_finalizer_lock ();
  
  	domains_to_finalize = g_slist_append (domains_to_finalize, req);
  
  	mono_finalizer_unlock ();
  
  	/* Tell the finalizer thread to finalize this appdomain */
  	mono_gc_finalize_notify ();
  
  	if (timeout == -1)
  		timeout = INFINITE;
  
  	while (TRUE) {
  		res = guarded_wait (done_event, timeout, TRUE);
  		/* printf ("WAIT RES: %d.\n", res); */
  
  		if (res == WAIT_IO_COMPLETION) {
  			if ((thread->state & (ThreadState_StopRequested | ThreadState_SuspendRequested)) != 0)
  				return FALSE;
  		} else if (res == WAIT_TIMEOUT) {
  			/* We leak the handle here */
  			return FALSE;
  		} else {
  			break;
  		}
  	}
  
  	CloseHandle (done_event);
  
  	if (domain == mono_get_root_domain ()) {
  		mono_threadpool_ms_cleanup ();
  		mono_gc_finalize_threadpool_threads ();
  	}
  
  	return TRUE;
  }
  
  void
  ves_icall_System_GC_InternalCollect (int generation)
  {
  	mono_gc_collect (generation);
  }
  
  gint64
  ves_icall_System_GC_GetTotalMemory (MonoBoolean forceCollection)
  {
  	if (forceCollection)
  		mono_gc_collect (mono_gc_max_generation ());
  	return mono_gc_get_used_size ();
  }
  
  void
  ves_icall_System_GC_KeepAlive (MonoObject *obj)
  {
  	/*
  	 * Does nothing.
  	 */
  }
  
  void
  ves_icall_System_GC_ReRegisterForFinalize (MonoObject *obj)
  {
  	MONO_CHECK_ARG_NULL (obj,);
  
  	object_register_finalizer (obj, mono_gc_run_finalize);
  }
  
  void
  ves_icall_System_GC_SuppressFinalize (MonoObject *obj)
  {
  	MONO_CHECK_ARG_NULL (obj,);
  
  	/* delegates have no finalizers, but we register them to deal with the
  	 * unmanaged->managed trampoline. We don't let the user suppress it
  	 * otherwise we'd leak it.
  	 */
  	if (obj->vtable->klass->delegate)
  		return;
  
  	/* FIXME: Need to handle case where obj has COM Callable Wrapper
  	 * generated for it that needs cleaned up, but user wants to suppress
  	 * their derived object finalizer. */
  
  	object_register_finalizer (obj, NULL);
  }
  
  void
  ves_icall_System_GC_WaitForPendingFinalizers (void)
  {
  	if (mono_gc_is_null ())
  		return;
  
  	if (!mono_gc_pending_finalizers ())
  		return;
  
  	if (mono_thread_internal_current () == gc_thread)
  		/* Avoid deadlocks */
  		return;
  
  	/*
  	If the finalizer thread is not live, lets pretend no finalizers are pending since the current thread might
  	be the one responsible for starting it up.
  	*/
  	if (gc_thread == NULL)
  		return;
  
  	ResetEvent (pending_done_event);
  	mono_gc_finalize_notify ();
  	/* g_print ("Waiting for pending finalizers....\n"); */
  	guarded_wait (pending_done_event, INFINITE, TRUE);
  	/* g_print ("Done pending....\n"); */
  }
  
  void
  ves_icall_System_GC_register_ephemeron_array (MonoObject *array)
  {
  #ifdef HAVE_SGEN_GC
  	if (!mono_gc_ephemeron_array_add (array)) {
  		mono_set_pending_exception (mono_object_domain (array)->out_of_memory_ex);
  		return;
  	}
  #endif
  }
  
  MonoObject*
  ves_icall_System_GC_get_ephemeron_tombstone (void)
  {
  	return mono_domain_get ()->ephemeron_tombstone;
  }
  
  #define mono_allocator_lock() mono_mutex_lock (&allocator_section)
  #define mono_allocator_unlock() mono_mutex_unlock (&allocator_section)
  static mono_mutex_t allocator_section;
  static mono_mutex_t handle_section;
  
  typedef enum {
  	HANDLE_WEAK,
  	HANDLE_WEAK_TRACK,
  	HANDLE_NORMAL,
  	HANDLE_PINNED
  } HandleType;
  
  static HandleType mono_gchandle_get_type (guint32 gchandle);
  
  MonoObject *
  ves_icall_System_GCHandle_GetTarget (guint32 handle)
  {
  	return mono_gchandle_get_target (handle);
  }
  
  /*
   * if type == -1, change the target of the handle, otherwise allocate a new handle.
   */
  guint32
  ves_icall_System_GCHandle_GetTargetHandle (MonoObject *obj, guint32 handle, gint32 type)
  {
  	if (type == -1) {
  		mono_gchandle_set_target (handle, obj);
  		/* the handle doesn't change */
  		return handle;
  	}
  	switch (type) {
  	case HANDLE_WEAK:
  		return mono_gchandle_new_weakref (obj, FALSE);
  	case HANDLE_WEAK_TRACK:
  		return mono_gchandle_new_weakref (obj, TRUE);
  	case HANDLE_NORMAL:
  		return mono_gchandle_new (obj, FALSE);
  	case HANDLE_PINNED:
  		return mono_gchandle_new (obj, TRUE);
  	default:
  		g_assert_not_reached ();
  	}
  	return 0;
  }
  
  void
  ves_icall_System_GCHandle_FreeHandle (guint32 handle)
  {
  	mono_gchandle_free (handle);
  }
  
  gpointer
  ves_icall_System_GCHandle_GetAddrOfPinnedObject (guint32 handle)
  {
  	MonoObject *obj;
  
  	if (mono_gchandle_get_type (handle) != HANDLE_PINNED)
  		return (gpointer)-2;
  	obj = mono_gchandle_get_target (handle);
  	if (obj) {
  		MonoClass *klass = mono_object_class (obj);
  		if (klass == mono_defaults.string_class) {
  			return mono_string_chars ((MonoString*)obj);
  		} else if (klass->rank) {
  			return mono_array_addr ((MonoArray*)obj, char, 0);
  		} else {
  			/* the C# code will check and throw the exception */
  			/* FIXME: missing !klass->blittable test, see bug #61134 */
  			if ((klass->flags & TYPE_ATTRIBUTE_LAYOUT_MASK) == TYPE_ATTRIBUTE_AUTO_LAYOUT)
  				return (gpointer)-1;
  			return (char*)obj + sizeof (MonoObject);
  		}
  	}
  	return NULL;
  }
  
  MonoBoolean
  ves_icall_Mono_Runtime_SetGCAllowSynchronousMajor (MonoBoolean flag)
  {
  	return mono_gc_set_allow_synchronous_major (flag);
  }
  
  typedef struct {
  	guint32  *bitmap;
  	gpointer *entries;
  	guint32   size;
  	guint8    type;
  	guint     slot_hint : 24; /* starting slot for search */
  	/* 2^16 appdomains should be enough for everyone (though I know I'll regret this in 20 years) */
  	/* we alloc this only for weak refs, since we can get the domain directly in the other cases */
  	guint16  *domain_ids;
  } HandleData;
  
  /* weak and weak-track arrays will be allocated in malloc memory 
   */
  static HandleData gc_handles [] = {
  	{NULL, NULL, 0, HANDLE_WEAK, 0},
  	{NULL, NULL, 0, HANDLE_WEAK_TRACK, 0},
  	{NULL, NULL, 0, HANDLE_NORMAL, 0},
  	{NULL, NULL, 0, HANDLE_PINNED, 0}
  };
  
  #define lock_handles(handles) mono_mutex_lock (&handle_section)
  #define unlock_handles(handles) mono_mutex_unlock (&handle_section)
  
  static int
  find_first_unset (guint32 bitmap)
  {
  	int i;
  	for (i = 0; i < 32; ++i) {
  		if (!(bitmap & (1 << i)))
  			return i;
  	}
  	return -1;
  }
  
  static MonoGCDescriptor
  make_root_descr_all_refs (int numbits, gboolean pinned)
  {
  #ifdef HAVE_SGEN_GC
  	if (pinned)
  		return MONO_GC_DESCRIPTOR_NULL;
  #endif
  	return mono_gc_make_root_descr_all_refs (numbits);
  }
  
  static guint32
  alloc_handle (HandleData *handles, MonoObject *obj, gboolean track)
  {
  	gint slot, i;
  	guint32 res;
  	lock_handles (handles);
  	if (!handles->size) {
  		handles->size = 32;
  		if (handles->type > HANDLE_WEAK_TRACK) {
  			handles->entries = mono_gc_alloc_fixed (sizeof (gpointer) * handles->size, make_root_descr_all_refs (handles->size, handles->type == HANDLE_PINNED));
  		} else {
  			handles->entries = g_malloc0 (sizeof (gpointer) * handles->size);
  			handles->domain_ids = g_malloc0 (sizeof (guint16) * handles->size);
  		}
  		handles->bitmap = g_malloc0 (handles->size / 8);
  	}
  	i = -1;
  	for (slot = handles->slot_hint; slot < handles->size / 32; ++slot) {
  		if (handles->bitmap [slot] != 0xffffffff) {
  			i = find_first_unset (handles->bitmap [slot]);
  			handles->slot_hint = slot;
  			break;
  		}
  	}
  	if (i == -1 && handles->slot_hint != 0) {
  		for (slot = 0; slot < handles->slot_hint; ++slot) {
  			if (handles->bitmap [slot] != 0xffffffff) {
  				i = find_first_unset (handles->bitmap [slot]);
  				handles->slot_hint = slot;
  				break;
  			}
  		}
  	}
  	if (i == -1) {
  		guint32 *new_bitmap;
  		guint32 new_size = handles->size * 2; /* always double: we memset to 0 based on this below */
  
  		/* resize and copy the bitmap */
  		new_bitmap = g_malloc0 (new_size / 8);
  		memcpy (new_bitmap, handles->bitmap, handles->size / 8);
  		g_free (handles->bitmap);
  		handles->bitmap = new_bitmap;
  
  		/* resize and copy the entries */
  		if (handles->type > HANDLE_WEAK_TRACK) {
  			gpointer *entries;
  
  			entries = mono_gc_alloc_fixed (sizeof (gpointer) * new_size, make_root_descr_all_refs (new_size, handles->type == HANDLE_PINNED));
  			mono_gc_memmove_aligned (entries, handles->entries, sizeof (gpointer) * handles->size);
  
  			mono_gc_free_fixed (handles->entries);
  			handles->entries = entries;
  		} else {
  			gpointer *entries;
  			guint16 *domain_ids;
  			domain_ids = g_malloc0 (sizeof (guint16) * new_size);
  			entries = g_malloc0 (sizeof (gpointer) * new_size);
  			memcpy (domain_ids, handles->domain_ids, sizeof (guint16) * handles->size);
  			for (i = 0; i < handles->size; ++i) {
  				MonoObject *obj = mono_gc_weak_link_get (&(handles->entries [i]));
  				if (obj) {
  					mono_gc_weak_link_add (&(entries [i]), obj, track);
  					mono_gc_weak_link_remove (&(handles->entries [i]), track);
  				} else {
  					g_assert (!handles->entries [i]);
  				}
  			}
  			g_free (handles->entries);
  			g_free (handles->domain_ids);
  			handles->entries = entries;
  			handles->domain_ids = domain_ids;
  		}
  
  		/* set i and slot to the next free position */
  		i = 0;
  		slot = (handles->size + 1) / 32;
  		handles->slot_hint = handles->size + 1;
  		handles->size = new_size;
  	}
  	handles->bitmap [slot] |= 1 << i;
  	slot = slot * 32 + i;
  	handles->entries [slot] = NULL;
  	if (handles->type <= HANDLE_WEAK_TRACK) {
  		/*FIXME, what to use when obj == null?*/
  		handles->domain_ids [slot] = (obj ? mono_object_get_domain (obj) : mono_domain_get ())->domain_id;
  		if (obj)
  			mono_gc_weak_link_add (&(handles->entries [slot]), obj, track);
  	} else {
  		handles->entries [slot] = obj;
  	}
  
  #ifndef DISABLE_PERFCOUNTERS
  	mono_perfcounters->gc_num_handles++;
  #endif
  	unlock_handles (handles);
  	/*g_print ("allocated entry %d of type %d to object %p (in slot: %p)\n", slot, handles->type, obj, handles->entries [slot]);*/
  	res = (slot << 3) | (handles->type + 1);
  	mono_profiler_gc_handle (MONO_PROFILER_GC_HANDLE_CREATED, handles->type, res, obj);
  	return res;
  }
  
  /**
   * mono_gchandle_new:
   * @obj: managed object to get a handle for
   * @pinned: whether the object should be pinned
   *
   * This returns a handle that wraps the object, this is used to keep a
   * reference to a managed object from the unmanaged world and preventing the
   * object from being disposed.
   * 
   * If @pinned is false the address of the object can not be obtained, if it is
   * true the address of the object can be obtained.  This will also pin the
   * object so it will not be possible by a moving garbage collector to move the
   * object. 
   * 
   * Returns: a handle that can be used to access the object from
   * unmanaged code.
   */
  guint32
  mono_gchandle_new (MonoObject *obj, gboolean pinned)
  {
  	return alloc_handle (&gc_handles [pinned? HANDLE_PINNED: HANDLE_NORMAL], obj, FALSE);
  }
  
  /**
   * mono_gchandle_new_weakref:
   * @obj: managed object to get a handle for
   * @pinned: whether the object should be pinned
   *
   * This returns a weak handle that wraps the object, this is used to
   * keep a reference to a managed object from the unmanaged world.
   * Unlike the mono_gchandle_new the object can be reclaimed by the
   * garbage collector.  In this case the value of the GCHandle will be
   * set to zero.
   * 
   * If @pinned is false the address of the object can not be obtained, if it is
   * true the address of the object can be obtained.  This will also pin the
   * object so it will not be possible by a moving garbage collector to move the
   * object. 
   * 
   * Returns: a handle that can be used to access the object from
   * unmanaged code.
   */
  guint32
  mono_gchandle_new_weakref (MonoObject *obj, gboolean track_resurrection)
  {
  	guint32 handle = alloc_handle (&gc_handles [track_resurrection? HANDLE_WEAK_TRACK: HANDLE_WEAK], obj, track_resurrection);
  
  	return handle;
  }
  
  static HandleType
  mono_gchandle_get_type (guint32 gchandle)
  {
  	guint type = (gchandle & 7) - 1;
  
  	return type;
  }
  
  /**
   * mono_gchandle_get_target:
   * @gchandle: a GCHandle's handle.
   *
   * The handle was previously created by calling mono_gchandle_new or
   * mono_gchandle_new_weakref. 
   *
   * Returns a pointer to the MonoObject represented by the handle or
   * NULL for a collected object if using a weakref handle.
   */
  MonoObject*
  mono_gchandle_get_target (guint32 gchandle)
  {
  	guint slot = gchandle >> 3;
  	guint type = (gchandle & 7) - 1;
  	HandleData *handles = &gc_handles [type];
  	MonoObject *obj = NULL;
  	if (type > 3)
  		return NULL;
  	lock_handles (handles);
  	if (slot < handles->size && (handles->bitmap [slot / 32] & (1 << (slot % 32)))) {
  		if (handles->type <= HANDLE_WEAK_TRACK) {
  			obj = mono_gc_weak_link_get (&handles->entries [slot]);
  		} else {
  			obj = handles->entries [slot];
  		}
  	} else {
  		/* print a warning? */
  	}
  	unlock_handles (handles);
  	/*g_print ("get target of entry %d of type %d: %p\n", slot, handles->type, obj);*/
  	return obj;
  }
  
  static void
  mono_gchandle_set_target (guint32 gchandle, MonoObject *obj)
  {
  	guint slot = gchandle >> 3;
  	guint type = (gchandle & 7) - 1;
  	HandleData *handles = &gc_handles [type];
  
  	if (type > 3)
  		return;
  	lock_handles (handles);
  	if (slot < handles->size && (handles->bitmap [slot / 32] & (1 << (slot % 32)))) {
  		if (handles->type <= HANDLE_WEAK_TRACK) {
  			if (handles->entries [slot])
  				mono_gc_weak_link_remove (&handles->entries [slot], handles->type == HANDLE_WEAK_TRACK);
  			if (obj)
  				mono_gc_weak_link_add (&handles->entries [slot], obj, handles->type == HANDLE_WEAK_TRACK);
  			/*FIXME, what to use when obj == null?*/
  			handles->domain_ids [slot] = (obj ? mono_object_get_domain (obj) : mono_domain_get ())->domain_id;
  		} else {
  			handles->entries [slot] = obj;
  		}
  	} else {
  		/* print a warning? */
  	}
  	/*g_print ("changed entry %d of type %d to object %p (in slot: %p)\n", slot, handles->type, obj, handles->entries [slot]);*/
  	unlock_handles (handles);
  }
  
  /**
   * mono_gchandle_is_in_domain:
   * @gchandle: a GCHandle's handle.
   * @domain: An application domain.
   *
   * Returns: true if the object wrapped by the @gchandle belongs to the specific @domain.
   */
  gboolean
  mono_gchandle_is_in_domain (guint32 gchandle, MonoDomain *domain)
  {
  	guint slot = gchandle >> 3;
  	guint type = (gchandle & 7) - 1;
  	HandleData *handles = &gc_handles [type];
  	gboolean result = FALSE;
  	if (type > 3)
  		return FALSE;
  	lock_handles (handles);
  	if (slot < handles->size && (handles->bitmap [slot / 32] & (1 << (slot % 32)))) {
  		if (handles->type <= HANDLE_WEAK_TRACK) {
  			result = domain->domain_id == handles->domain_ids [slot];
  		} else {
  			MonoObject *obj;
  			obj = handles->entries [slot];
  			if (obj == NULL)
  				result = TRUE;
  			else
  				result = domain == mono_object_domain (obj);
  		}
  	} else {
  		/* print a warning? */
  	}
  	unlock_handles (handles);
  	return result;
  }
  
  /**
   * mono_gchandle_free:
   * @gchandle: a GCHandle's handle.
   *
   * Frees the @gchandle handle.  If there are no outstanding
   * references, the garbage collector can reclaim the memory of the
   * object wrapped. 
   */
  void
  mono_gchandle_free (guint32 gchandle)
  {
  	guint slot = gchandle >> 3;
  	guint type = (gchandle & 7) - 1;
  	HandleData *handles = &gc_handles [type];
  	if (type > 3)
  		return;
  
  	lock_handles (handles);
  	if (slot < handles->size && (handles->bitmap [slot / 32] & (1 << (slot % 32)))) {
  		if (handles->type <= HANDLE_WEAK_TRACK) {
  			if (handles->entries [slot])
  				mono_gc_weak_link_remove (&handles->entries [slot], handles->type == HANDLE_WEAK_TRACK);
  		} else {
  			handles->entries [slot] = NULL;
  		}
  		handles->bitmap [slot / 32] &= ~(1 << (slot % 32));
  	} else {
  		/* print a warning? */
  	}
  #ifndef DISABLE_PERFCOUNTERS
  	mono_perfcounters->gc_num_handles--;
  #endif
  	/*g_print ("freed entry %d of type %d\n", slot, handles->type);*/
  	unlock_handles (handles);
  	mono_profiler_gc_handle (MONO_PROFILER_GC_HANDLE_DESTROYED, handles->type, gchandle, NULL);
  }
  
  /**
   * mono_gchandle_free_domain:
   * @domain: domain that is unloading
   *
   * Function used internally to cleanup any GC handle for objects belonging
   * to the specified domain during appdomain unload.
   */
  void
  mono_gchandle_free_domain (MonoDomain *domain)
  {
  	guint type;
  
  	for (type = 0; type < 3; ++type) {
  		guint slot;
  		HandleData *handles = &gc_handles [type];
  		lock_handles (handles);
  		for (slot = 0; slot < handles->size; ++slot) {
  			if (!(handles->bitmap [slot / 32] & (1 << (slot % 32))))
  				continue;
  			if (type <= HANDLE_WEAK_TRACK) {
  				if (domain->domain_id == handles->domain_ids [slot]) {
  					handles->bitmap [slot / 32] &= ~(1 << (slot % 32));
  					if (handles->entries [slot])
  						mono_gc_weak_link_remove (&handles->entries [slot], handles->type == HANDLE_WEAK_TRACK);
  				}
  			} else {
  				if (handles->entries [slot] && mono_object_domain (handles->entries [slot]) == domain) {
  					handles->bitmap [slot / 32] &= ~(1 << (slot % 32));
  					handles->entries [slot] = NULL;
  				}
  			}
  		}
  		unlock_handles (handles);
  	}
  
  }
  
  MonoBoolean
  mono_gc_GCHandle_CheckCurrentDomain (guint32 gchandle)
  {
  	return mono_gchandle_is_in_domain (gchandle, mono_domain_get ());
  }
  
  #ifdef MONO_HAS_SEMAPHORES
  static MonoSemType finalizer_sem;
  #endif
  static HANDLE finalizer_event;
  static volatile gboolean finished=FALSE;
  
  void
  mono_gc_finalize_notify (void)
  {
  #ifdef DEBUG
  	g_message ( "%s: prodding finalizer", __func__);
  #endif
  
  	if (mono_gc_is_null ())
  		return;
  
  #ifdef MONO_HAS_SEMAPHORES
  	MONO_SEM_POST (&finalizer_sem);
  #else
  	SetEvent (finalizer_event);
  #endif
  }
  
  #ifdef HAVE_BOEHM_GC
  
  static void
  collect_objects (gpointer key, gpointer value, gpointer user_data)
  {
  	GPtrArray *arr = (GPtrArray*)user_data;
  	g_ptr_array_add (arr, key);
  }
  
  #endif
  
  /*
   * finalize_domain_objects:
   *
   *  Run the finalizers of all finalizable objects in req->domain.
   */
  static void
  finalize_domain_objects (DomainFinalizationReq *req)
  {
  	MonoDomain *domain = req->domain;
  
  #if HAVE_SGEN_GC
  #define NUM_FOBJECTS 64
  	MonoObject *to_finalize [NUM_FOBJECTS];
  	int count;
  #endif
  
  	/* Process finalizers which are already in the queue */
  	mono_gc_invoke_finalizers ();
  
  #ifdef HAVE_BOEHM_GC
  	while (g_hash_table_size (domain->finalizable_objects_hash) > 0) {
  		int i;
  		GPtrArray *objs;
  		/* 
  		 * Since the domain is unloading, nobody is allowed to put
  		 * new entries into the hash table. But finalize_object might
  		 * remove entries from the hash table, so we make a copy.
  		 */
  		objs = g_ptr_array_new ();
  		g_hash_table_foreach (domain->finalizable_objects_hash, collect_objects, objs);
  		/* printf ("FINALIZING %d OBJECTS.\n", objs->len); */
  
  		for (i = 0; i < objs->len; ++i) {
  			MonoObject *o = (MonoObject*)g_ptr_array_index (objs, i);
  			/* FIXME: Avoid finalizing threads, etc */
  			mono_gc_run_finalize (o, 0);
  		}
  
  		g_ptr_array_free (objs, TRUE);
  	}
  #elif defined(HAVE_SGEN_GC)
  	while ((count = mono_gc_finalizers_for_domain (domain, to_finalize, NUM_FOBJECTS))) {
  		int i;
  		for (i = 0; i < count; ++i) {
  			mono_gc_run_finalize (to_finalize [i], 0);
  		}
  	}
  #endif
  
  	/* cleanup the reference queue */
  	reference_queue_clear_for_domain (domain);
  	
  	/* printf ("DONE.\n"); */
  	SetEvent (req->done_event);
  
  	/* The event is closed in mono_domain_finalize if we get here */
  	g_free (req);
  }
  
  static guint32
  finalizer_thread (gpointer unused)
  {
  	gboolean wait = TRUE;
  
  	while (!finished) {
  		/* Wait to be notified that there's at least one
  		 * finaliser to run
  		 */
  
  		g_assert (mono_domain_get () == mono_get_root_domain ());
  		mono_gc_set_skip_thread (TRUE);
  		MONO_PREPARE_BLOCKING
  
  		if (wait) {
  		/* An alertable wait is required so this thread can be suspended on windows */
  #ifdef MONO_HAS_SEMAPHORES
  			MONO_SEM_WAIT_ALERTABLE (&finalizer_sem, TRUE);
  #else
  			WaitForSingleObjectEx (finalizer_event, INFINITE, TRUE);
  #endif
  		}
  		wait = TRUE;
  		MONO_FINISH_BLOCKING
  		mono_gc_set_skip_thread (FALSE);
  
  		mono_threads_perform_thread_dump ();
  
  		mono_console_handle_async_ops ();
  
  		mono_attach_maybe_start ();
  
  		if (domains_to_finalize) {
  			mono_finalizer_lock ();
  			if (domains_to_finalize) {
  				DomainFinalizationReq *req = domains_to_finalize->data;
  				domains_to_finalize = g_slist_remove (domains_to_finalize, req);
  				mono_finalizer_unlock ();
  
  				finalize_domain_objects (req);
  			} else {
  				mono_finalizer_unlock ();
  			}
  		}				
  
  		/* If finished == TRUE, mono_gc_cleanup has been called (from mono_runtime_cleanup),
  		 * before the domain is unloaded.
  		 */
  		mono_gc_invoke_finalizers ();
  
  		mono_threads_join_threads ();
  
  		reference_queue_proccess_all ();
  
  #ifdef MONO_HAS_SEMAPHORES
  		/* Avoid posting the pending done event until there are pending finalizers */
  		if (MONO_SEM_TIMEDWAIT (&finalizer_sem, 0) == 0)
  			/* Don't wait again at the start of the loop */
  			wait = FALSE;
  		else
  			SetEvent (pending_done_event);
  #else
  			SetEvent (pending_done_event);
  #endif
  	}
  
  	mono_finalizer_lock ();
  	finalizer_thread_exited = TRUE;
  	mono_cond_signal (&exited_cond);
  	mono_finalizer_unlock ();
  
  	return 0;
  }
  
  #ifndef LAZY_GC_THREAD_CREATION
  static
  #endif
  void
  mono_gc_init_finalizer_thread (void)
  {
  	gc_thread = mono_thread_create_internal (mono_domain_get (), finalizer_thread, NULL, FALSE, 0);
  	ves_icall_System_Threading_Thread_SetName_internal (gc_thread, mono_string_new (mono_domain_get (), "Finalizer"));
  }
  
  void
  mono_gc_init (void)
  {
  	mono_mutex_init_recursive (&handle_section);
  	mono_mutex_init_recursive (&allocator_section);
  
  	mono_mutex_init_recursive (&finalizer_mutex);
  	mono_mutex_init_recursive (&reference_queue_mutex);
  
  	MONO_GC_REGISTER_ROOT_FIXED (gc_handles [HANDLE_NORMAL].entries);
  	MONO_GC_REGISTER_ROOT_FIXED (gc_handles [HANDLE_PINNED].entries);
  
  	mono_counters_register ("Minor GC collections", MONO_COUNTER_GC | MONO_COUNTER_UINT, &gc_stats.minor_gc_count);
  	mono_counters_register ("Major GC collections", MONO_COUNTER_GC | MONO_COUNTER_UINT, &gc_stats.major_gc_count);
  	mono_counters_register ("Minor GC time", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.minor_gc_time);
  	mono_counters_register ("Major GC time", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.major_gc_time);
  	mono_counters_register ("Major GC time concurrent", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.major_gc_time_concurrent);
  
  	mono_gc_base_init ();
  
  	if (mono_gc_is_disabled ()) {
  		gc_disabled = TRUE;
  		return;
  	}
  	
  	finalizer_event = CreateEvent (NULL, FALSE, FALSE, NULL);
  	g_assert (finalizer_event);
  	pending_done_event = CreateEvent (NULL, TRUE, FALSE, NULL);
  	g_assert (pending_done_event);
  	mono_cond_init (&exited_cond, 0);
  #ifdef MONO_HAS_SEMAPHORES
  	MONO_SEM_INIT (&finalizer_sem, 0);
  #endif
  
  #ifndef LAZY_GC_THREAD_CREATION
  	mono_gc_init_finalizer_thread ();
  #endif
  }
  
  void
  mono_gc_cleanup (void)
  {
  #ifdef DEBUG
  	g_message ("%s: cleaning up finalizer", __func__);
  #endif
  
  	if (mono_gc_is_null ())
  		return;
  
  	if (!gc_disabled) {
  		finished = TRUE;
  		if (mono_thread_internal_current () != gc_thread) {
  			gboolean timed_out = FALSE;
  			guint32 start_ticks = mono_msec_ticks ();
  			guint32 end_ticks = start_ticks + 2000;
  
  			mono_gc_finalize_notify ();
  			/* Finishing the finalizer thread, so wait a little bit... */
  			/* MS seems to wait for about 2 seconds */
  			while (!finalizer_thread_exited) {
  				guint32 current_ticks = mono_msec_ticks ();
  				guint32 timeout;
  
  				if (current_ticks >= end_ticks)
  					break;
  				else
  					timeout = end_ticks - current_ticks;
  				MONO_PREPARE_BLOCKING;
  				mono_finalizer_lock ();
  				if (!finalizer_thread_exited)
  					mono_cond_timedwait_ms (&exited_cond, &finalizer_mutex, timeout);
  				mono_finalizer_unlock ();
  				MONO_FINISH_BLOCKING;
  			}
  
  			if (!finalizer_thread_exited) {
  				int ret;
  
  				/* Set a flag which the finalizer thread can check */
  				suspend_finalizers = TRUE;
  
  				/* Try to abort the thread, in the hope that it is running managed code */
  				mono_thread_internal_stop (gc_thread);
  
  				/* Wait for it to stop */
  				ret = guarded_wait (gc_thread->handle, 100, TRUE);
  
  				if (ret == WAIT_TIMEOUT) {
  					/* 
  					 * The finalizer thread refused to die. There is not much we 
  					 * can do here, since the runtime is shutting down so the 
  					 * state the finalizer thread depends on will vanish.
  					 */
  					g_warning ("Shutting down finalizer thread timed out.");
  					timed_out = TRUE;
  				}
  			}
  
  			if (!timed_out) {
  				int ret;
  
  				/* Wait for the thread to actually exit */
  				ret = guarded_wait (gc_thread->handle, INFINITE, TRUE);
  				g_assert (ret == WAIT_OBJECT_0);
  
  				mono_thread_join (GUINT_TO_POINTER (gc_thread->tid));
  			}
  		}
  		gc_thread = NULL;
  		mono_gc_base_cleanup ();
  	}
  
  	mono_reference_queue_cleanup ();
  
  	mono_mutex_destroy (&allocator_section);
  	mono_mutex_destroy (&finalizer_mutex);
  	mono_mutex_destroy (&reference_queue_mutex);
  }
  
  /**
   * mono_gc_mutex_cleanup:
   *
   * Destroy the mutexes that may still be used after the main cleanup routine.
   */
  void
  mono_gc_mutex_cleanup (void)
  {
  	mono_mutex_destroy (&handle_section);
  }
  
  gboolean
  mono_gc_is_finalizer_internal_thread (MonoInternalThread *thread)
  {
  	return thread == gc_thread;
  }
  
  /**
   * mono_gc_is_finalizer_thread:
   * @thread: the thread to test.
   *
   * In Mono objects are finalized asynchronously on a separate thread.
   * This routine tests whether the @thread argument represents the
   * finalization thread.
   * 
   * Returns true if @thread is the finalization thread.
   */
  gboolean
  mono_gc_is_finalizer_thread (MonoThread *thread)
  {
  	return mono_gc_is_finalizer_internal_thread (thread->internal_thread);
  }
  
  #if defined(__MACH__)
  static pthread_t mach_exception_thread;
  
  void
  mono_gc_register_mach_exception_thread (pthread_t thread)
  {
  	mach_exception_thread = thread;
  }
  
  pthread_t
  mono_gc_get_mach_exception_thread (void)
  {
  	return mach_exception_thread;
  }
  #endif
  
  #ifndef HAVE_SGEN_GC
  void*
  mono_gc_alloc_mature (MonoVTable *vtable)
  {
  	return mono_object_new_specific (vtable);
  }
  #endif
  
  
  static MonoReferenceQueue *ref_queues;
  
  static void
  ref_list_remove_element (RefQueueEntry **prev, RefQueueEntry *element)
  {
  	do {
  		/* Guard if head is changed concurrently. */
  		while (*prev != element)
  			prev = &(*prev)->next;
  	} while (prev && InterlockedCompareExchangePointer ((void*)prev, element->next, element) != element);
  }
  
  static void
  ref_list_push (RefQueueEntry **head, RefQueueEntry *value)
  {
  	RefQueueEntry *current;
  	do {
  		current = *head;
  		value->next = current;
  		STORE_STORE_FENCE; /*Must make sure the previous store is visible before the CAS. */
  	} while (InterlockedCompareExchangePointer ((void*)head, value, current) != current);
  }
  
  static void
  reference_queue_proccess (MonoReferenceQueue *queue)
  {
  	RefQueueEntry **iter = &queue->queue;
  	RefQueueEntry *entry;
  	while ((entry = *iter)) {
  #ifdef HAVE_SGEN_GC
  		if (queue->should_be_deleted || !mono_gc_weak_link_get (&entry->dis_link)) {
  			mono_gc_weak_link_remove (&entry->dis_link, TRUE);
  #else
  		if (queue->should_be_deleted || !mono_gchandle_get_target (entry->gchandle)) {
  			mono_gchandle_free ((guint32)entry->gchandle);
  #endif
  			ref_list_remove_element (iter, entry);
  			queue->callback (entry->user_data);
  			g_free (entry);
  		} else {
  			iter = &entry->next;
  		}
  	}
  }
  
  static void
  reference_queue_proccess_all (void)
  {
  	MonoReferenceQueue **iter;
  	MonoReferenceQueue *queue = ref_queues;
  	for (; queue; queue = queue->next)
  		reference_queue_proccess (queue);
  
  restart:
  	mono_mutex_lock (&reference_queue_mutex);
  	for (iter = &ref_queues; *iter;) {
  		queue = *iter;
  		if (!queue->should_be_deleted) {
  			iter = &queue->next;
  			continue;
  		}
  		if (queue->queue) {
  			mono_mutex_unlock (&reference_queue_mutex);
  			reference_queue_proccess (queue);
  			goto restart;
  		}
  		*iter = queue->next;
  		g_free (queue);
  	}
  	mono_mutex_unlock (&reference_queue_mutex);
  }
  
  static void
  mono_reference_queue_cleanup (void)
  {
  	MonoReferenceQueue *queue = ref_queues;
  	for (; queue; queue = queue->next)
  		queue->should_be_deleted = TRUE;
  	reference_queue_proccess_all ();
  }
  
  static void
  reference_queue_clear_for_domain (MonoDomain *domain)
  {
  	MonoReferenceQueue *queue = ref_queues;
  	for (; queue; queue = queue->next) {
  		RefQueueEntry **iter = &queue->queue;
  		RefQueueEntry *entry;
  		while ((entry = *iter)) {
  			if (entry->domain == domain) {
  #ifdef HAVE_SGEN_GC
  				mono_gc_weak_link_remove (&entry->dis_link, TRUE);
  #else
  				mono_gchandle_free ((guint32)entry->gchandle);
  #endif
  				ref_list_remove_element (iter, entry);
  				queue->callback (entry->user_data);
  				g_free (entry);
  			} else {
  				iter = &entry->next;
  			}
  		}
  	}
  }
  /**
   * mono_gc_reference_queue_new:
   * @callback callback used when processing collected entries.
   *
   * Create a new reference queue used to process collected objects.
   * A reference queue let you add a pair of (managed object, user data)
   * using the mono_gc_reference_queue_add method.
   *
   * Once the managed object is collected @callback will be called
   * in the finalizer thread with 'user data' as argument.
   *
   * The callback is called from the finalizer thread without any locks held.
   * When a AppDomain is unloaded, all callbacks for objects belonging to it
   * will be invoked.
   *
   * @returns the new queue.
   */
  MonoReferenceQueue*
  mono_gc_reference_queue_new (mono_reference_queue_callback callback)
  {
  	MonoReferenceQueue *res = g_new0 (MonoReferenceQueue, 1);
  	res->callback = callback;
  
  	mono_mutex_lock (&reference_queue_mutex);
  	res->next = ref_queues;
  	ref_queues = res;
  	mono_mutex_unlock (&reference_queue_mutex);
  
  	return res;
  }
  
  /**
   * mono_gc_reference_queue_add:
   * @queue the queue to add the reference to.
   * @obj the object to be watched for collection
   * @user_data parameter to be passed to the queue callback
   *
   * Queue an object to be watched for collection, when the @obj is
   * collected, the callback that was registered for the @queue will
   * be invoked with @user_data as argument.
   *
   * @returns false if the queue is scheduled to be freed.
   */
  gboolean
  mono_gc_reference_queue_add (MonoReferenceQueue *queue, MonoObject *obj, void *user_data)
  {
  	RefQueueEntry *entry;
  	if (queue->should_be_deleted)
  		return FALSE;
  
  	entry = g_new0 (RefQueueEntry, 1);
  	entry->user_data = user_data;
  	entry->domain = mono_object_domain (obj);
  
  #ifdef HAVE_SGEN_GC
  	mono_gc_weak_link_add (&entry->dis_link, obj, TRUE);
  #else
  	entry->gchandle = mono_gchandle_new_weakref (obj, TRUE);
  	mono_object_register_finalizer (obj);
  #endif
  
  	ref_list_push (&queue->queue, entry);
  	return TRUE;
  }
  
  /**
   * mono_gc_reference_queue_free:
   * @queue the queue that should be freed.
   *
   * This operation signals that @queue should be freed. This operation is deferred
   * as it happens on the finalizer thread.
   *
   * After this call, no further objects can be queued. It's the responsibility of the
   * caller to make sure that no further attempt to access queue will be made.
   */
  void
  mono_gc_reference_queue_free (MonoReferenceQueue *queue)
  {
  	queue->should_be_deleted = TRUE;
  }
  