1 /* GNU Objective C Runtime class related functions
2 Copyright (C) 1993, 1995, 1996, 1997, 2001, 2002, 2009, 2010
3 Free Software Foundation, Inc.
4 Contributed by Kresten Krab Thorup and Dennis Glatting.
6 Lock-free class table code designed and written from scratch by
9 This file is part of GCC.
11 GCC is free software; you can redistribute it and/or modify it under the
12 terms of the GNU General Public License as published by the Free Software
13 Foundation; either version 3, or (at your option) any later version.
15 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
16 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
20 Under Section 7 of GPL version 3, you are granted additional
21 permissions described in the GCC Runtime Library Exception, version
22 3.1, as published by the Free Software Foundation.
24 You should have received a copy of the GNU General Public License and
25 a copy of the GCC Runtime Library Exception along with this program;
26 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
27 <http://www.gnu.org/licenses/>. */
29 /* The code in this file critically affects class method invocation
30 speed. This long preamble comment explains why, and the issues
33 One of the traditional weaknesses of the GNU Objective-C runtime is
34 that class method invocations are slow. The reason is that when you
37 array = [NSArray new];
39 this gets basically compiled into the equivalent of
41 array = [(objc_get_class ("NSArray")) new];
43 objc_get_class returns the class pointer corresponding to the string
44 `NSArray'; and because of the lookup, the operation is more
45 complicated and slow than a simple instance method invocation.
47 Most high performance Objective-C code (using the GNU Objc runtime)
48 I had the opportunity to read (or write) work around this problem by
49 caching the class pointer:
51 Class arrayClass = [NSArray class];
55 array = [arrayClass new];
56 array = [arrayClass new];
57 array = [arrayClass new];
59 In this case, you always perform a class lookup (the first one), but
60 then all the [arrayClass new] methods run exactly as fast as an
61 instance method invocation. It helps if you have many class method
62 invocations to the same class.
64 The long-term solution to this problem would be to modify the
65 compiler to output tables of class pointers corresponding to all the
66 class method invocations, and to add code to the runtime to update
67 these tables - that should in the end allow class method invocations
68 to perform precisely as fast as instance method invocations, because
69 no class lookup would be involved. I think the Apple Objective-C
70 runtime uses this technique. Doing this involves synchronized
71 modifications in the runtime and in the compiler.
73 As a first medicine to the problem, I [NP] have redesigned and
74 rewritten the way the runtime is performing class lookup. This
75 doesn't give as much speed as the other (definitive) approach, but
76 at least a class method invocation now takes approximately 4.5 times
77 an instance method invocation on my machine (it would take approx 12
78 times before the rewriting), which is a lot better.
80 One of the main reason the new class lookup is so faster is because
81 I implemented it in a way that can safely run multithreaded without
82 using locks - a so-called `lock-free' data structure. The atomic
83 operation is pointer assignment. The reason why in this problem
84 lock-free data structures work so well is that you never remove
85 classes from the table - and the difficult thing with lock-free data
86 structures is freeing data when is removed from the structures. */
88 #include "objc-private/common.h"
89 #include "objc-private/error.h"
90 #include "objc/runtime.h"
92 #include "objc-private/module-abi-8.h" /* For CLS_ISCLASS and similar. */
93 #include "objc-private/runtime.h" /* the kitchen sink */
94 #include "objc-private/sarray.h" /* For sarray_put_at_safe. */
95 #include "objc-private/selector.h" /* For sarray_put_at_safe. */
96 #include <string.h> /* For memset */
98 /* We use a table which maps a class name to the corresponding class
99 pointer. The first part of this file defines this table, and
100 functions to do basic operations on the table. The second part of
101 the file implements some higher level Objective-C functionality for
102 classes by using the functions provided in the first part to manage
106 ** Class Table Internals
109 /* A node holding a class */
110 typedef struct class_node
112 struct class_node *next; /* Pointer to next entry on the list.
113 NULL indicates end of list. */
115 const char *name; /* The class name string */
116 int length; /* The class name string length */
117 Class pointer; /* The Class pointer */
121 /* A table containing classes is a class_node_ptr (pointing to the
122 first entry in the table - if it is NULL, then the table is
125 /* We have 1024 tables. Each table contains all class names which
126 have the same hash (which is a number between 0 and 1023). To look
127 up a class_name, we compute its hash, and get the corresponding
128 table. Once we have the table, we simply compare strings directly
129 till we find the one which we want (using the length first). The
130 number of tables is quite big on purpose (a normal big application
131 has less than 1000 classes), so that you shouldn't normally get any
132 collisions, and get away with a single comparison (which we can't
133 avoid since we need to know that you have got the right thing). */
134 #define CLASS_TABLE_SIZE 1024
135 #define CLASS_TABLE_MASK 1023
137 static class_node_ptr class_table_array[CLASS_TABLE_SIZE];
139 /* The table writing mutex - we lock on writing to avoid conflicts
140 between different writers, but we read without locks. That is
141 possible because we assume pointer assignment to be an atomic
142 operation. TODO: This is only true under certain circumstances,
143 which should be clarified. */
144 static objc_mutex_t __class_table_lock = NULL;
146 /* CLASS_TABLE_HASH is how we compute the hash of a class name. It is
147 a macro - *not* a function - arguments *are* modified directly.
149 INDEX should be a variable holding an int;
150 HASH should be a variable holding an int;
151 CLASS_NAME should be a variable holding a (char *) to the class_name.
153 After the macro is executed, INDEX contains the length of the
154 string, and HASH the computed hash of the string; CLASS_NAME is
157 #define CLASS_TABLE_HASH(INDEX, HASH, CLASS_NAME) \
159 for (INDEX = 0; CLASS_NAME[INDEX] != '\0'; INDEX++) \
161 HASH = (HASH << 4) ^ (HASH >> 28) ^ CLASS_NAME[INDEX]; \
164 HASH = (HASH ^ (HASH >> 10) ^ (HASH >> 20)) & CLASS_TABLE_MASK;
166 /* Setup the table. */
168 class_table_setup (void)
170 /* Start - nothing in the table. */
171 memset (class_table_array, 0, sizeof (class_node_ptr) * CLASS_TABLE_SIZE);
173 /* The table writing mutex. */
174 __class_table_lock = objc_mutex_allocate ();
178 /* Insert a class in the table (used when a new class is
181 class_table_insert (const char *class_name, Class class_pointer)
184 class_node_ptr new_node;
186 /* Find out the class name's hash and length. */
187 CLASS_TABLE_HASH (length, hash, class_name);
189 /* Prepare the new node holding the class. */
190 new_node = objc_malloc (sizeof (struct class_node));
191 new_node->name = class_name;
192 new_node->length = length;
193 new_node->pointer = class_pointer;
195 /* Lock the table for modifications. */
196 objc_mutex_lock (__class_table_lock);
198 /* Insert the new node in the table at the beginning of the table at
199 class_table_array[hash]. */
200 new_node->next = class_table_array[hash];
201 class_table_array[hash] = new_node;
203 objc_mutex_unlock (__class_table_lock);
206 /* Replace a class in the table (used only by poseAs:). */
208 class_table_replace (Class old_class_pointer, Class new_class_pointer)
213 objc_mutex_lock (__class_table_lock);
216 node = class_table_array[hash];
218 while (hash < CLASS_TABLE_SIZE)
223 if (hash < CLASS_TABLE_SIZE)
224 node = class_table_array[hash];
228 Class class1 = node->pointer;
230 if (class1 == old_class_pointer)
231 node->pointer = new_class_pointer;
237 objc_mutex_unlock (__class_table_lock);
241 /* Get a class from the table. This does not need mutex protection.
242 Currently, this function is called each time you call a static
243 method, this is why it must be very fast. */
245 class_table_get_safe (const char *class_name)
250 /* Compute length and hash. */
251 CLASS_TABLE_HASH (length, hash, class_name);
253 node = class_table_array[hash];
259 if (node->length == length)
261 /* Compare the class names. */
264 for (i = 0; i < length; i++)
266 if ((node->name)[i] != class_name[i])
272 /* They are equal! */
273 return node->pointer;
277 while ((node = node->next) != NULL);
283 /* Enumerate over the class table. */
284 struct class_table_enumerator
292 class_table_next (struct class_table_enumerator **e)
294 struct class_table_enumerator *enumerator = *e;
297 if (enumerator == NULL)
299 *e = objc_malloc (sizeof (struct class_table_enumerator));
301 enumerator->hash = 0;
302 enumerator->node = NULL;
304 next = class_table_array[enumerator->hash];
307 next = enumerator->node->next;
311 enumerator->node = next;
312 return enumerator->node->pointer;
318 while (enumerator->hash < CLASS_TABLE_SIZE)
320 next = class_table_array[enumerator->hash];
323 enumerator->node = next;
324 return enumerator->node->pointer;
329 /* Ok - table finished - done. */
330 objc_free (enumerator);
335 #if 0 /* DEBUGGING FUNCTIONS */
336 /* Debugging function - print the class table. */
338 class_table_print (void)
342 for (i = 0; i < CLASS_TABLE_SIZE; i++)
347 node = class_table_array[i];
351 printf ("\t%s\n", node->name);
357 /* Debugging function - print an histogram of number of classes in
358 function of hash key values. Useful to evaluate the hash function
361 class_table_print_histogram (void)
366 for (i = 0; i < CLASS_TABLE_SIZE; i++)
370 node = class_table_array[i];
377 if (((i + 1) % 50) == 0)
379 printf ("%4d:", i + 1);
380 for (j = 0; j < counter; j++)
387 printf ("%4d:", i + 1);
388 for (j = 0; j < counter; j++)
393 #endif /* DEBUGGING FUNCTIONS */
396 ** Objective-C runtime functions
399 /* From now on, the only access to the class table data structure
400 should be via the class_table_* functions. */
402 /* This is a hook which is called by objc_get_class and
403 objc_lookup_class if the runtime is not able to find the class.
404 This may e.g. try to load in the class using dynamic loading.
406 This hook was a public, global variable in the Traditional GNU
407 Objective-C Runtime API (objc/objc-api.h). The modern GNU
408 Objective-C Runtime API (objc/runtime.h) provides the
409 objc_setGetUnknownClassHandler() function instead.
411 Class (*_objc_lookup_class) (const char *name) = 0; /* !T:SAFE */
413 /* The handler currently in use. PS: if both
414 __obj_get_unknown_class_handler and _objc_lookup_class are defined,
415 __objc_get_unknown_class_handler is called first. */
416 static objc_get_unknown_class_handler
417 __objc_get_unknown_class_handler = NULL;
419 objc_get_unknown_class_handler
420 objc_setGetUnknownClassHandler (objc_get_unknown_class_handler
423 objc_get_unknown_class_handler old_handler
424 = __objc_get_unknown_class_handler;
425 __objc_get_unknown_class_handler = new_handler;
430 /* True when class links has been resolved. */
431 BOOL __objc_class_links_resolved = NO; /* !T:UNUSED */
435 __objc_init_class_tables (void)
437 /* Allocate the class hash table. */
439 if (__class_table_lock)
442 objc_mutex_lock (__objc_runtime_mutex);
444 class_table_setup ();
446 objc_mutex_unlock (__objc_runtime_mutex);
449 /* This function adds a class to the class hash table, and assigns the
450 class a number, unless it's already known. Return 'YES' if the
451 class was added. Return 'NO' if the class was already known. */
453 __objc_add_class_to_hash (Class class)
455 Class existing_class;
457 objc_mutex_lock (__objc_runtime_mutex);
459 /* Make sure the table is there. */
460 assert (__class_table_lock);
462 /* Make sure it's not a meta class. */
463 assert (CLS_ISCLASS (class));
465 /* Check to see if the class is already in the hash table. */
466 existing_class = class_table_get_safe (class->name);
470 objc_mutex_unlock (__objc_runtime_mutex);
475 /* The class isn't in the hash table. Add the class and assign
477 static unsigned int class_number = 1;
479 CLS_SETNUMBER (class, class_number);
480 CLS_SETNUMBER (class->class_pointer, class_number);
483 class_table_insert (class->name, class);
485 objc_mutex_unlock (__objc_runtime_mutex);
491 objc_getClass (const char *name)
498 class = class_table_get_safe (name);
503 if (__objc_get_unknown_class_handler)
504 return (*__objc_get_unknown_class_handler) (name);
506 if (_objc_lookup_class)
507 return (*_objc_lookup_class) (name);
513 objc_lookUpClass (const char *name)
518 return class_table_get_safe (name);
522 objc_getMetaClass (const char *name)
524 Class class = objc_getClass (name);
527 return class->class_pointer;
533 objc_getRequiredClass (const char *name)
535 Class class = objc_getClass (name);
540 _objc_abort ("objc_getRequiredClass ('%s') failed: class not found\n", name);
544 objc_getClassList (Class *returnValue, int maxNumberOfClassesToReturn)
546 /* Iterate over all entries in the table. */
549 for (hash = 0; hash < CLASS_TABLE_SIZE; hash++)
551 class_node_ptr node = class_table_array[hash];
557 if (count < maxNumberOfClassesToReturn)
558 returnValue[count] = node->pointer;
571 objc_allocateClassPair (Class super_class, const char *class_name, size_t extraBytes)
574 Class new_meta_class;
576 if (class_name == NULL)
579 if (objc_getClass (class_name))
584 /* If you want to build a hierarchy of classes, you need to
585 build and register them one at a time. The risk is that you
586 are able to cause confusion by registering a subclass before
587 the superclass or similar. */
588 if (CLS_IS_IN_CONSTRUCTION (super_class))
592 /* Technically, we should create the metaclass first, then use
593 class_createInstance() to create the class. That complication
594 would be relevant if we had class variables, but we don't, so we
595 just ignore it and create everything directly and assume all
596 classes have the same size. */
597 new_class = objc_calloc (1, sizeof (struct objc_class) + extraBytes);
598 new_meta_class = objc_calloc (1, sizeof (struct objc_class) + extraBytes);
600 /* We create an unresolved class, similar to one generated by the
601 compiler. It will be resolved later when we register it.
603 Note how the metaclass details are not that important; when the
604 class is resolved, the ones that matter will be fixed up. */
605 new_class->class_pointer = new_meta_class;
606 new_meta_class->class_pointer = 0;
610 /* Force the name of the superclass in place of the link to the
611 actual superclass, which will be put there when the class is
613 const char *super_class_name = class_getName (super_class);
614 new_class->super_class = (void *)super_class_name;
615 new_meta_class->super_class = (void *)super_class_name;
619 new_class->super_class = (void *)0;
620 new_meta_class->super_class = (void *)0;
623 new_class->name = objc_malloc (strlen (class_name) + 1);
624 strcpy ((char*)new_class->name, class_name);
625 new_meta_class->name = new_class->name;
627 new_class->version = 0;
628 new_meta_class->version = 0;
630 new_class->info = _CLS_CLASS | _CLS_IN_CONSTRUCTION;
631 new_meta_class->info = _CLS_META | _CLS_IN_CONSTRUCTION;
634 new_class->instance_size = super_class->instance_size;
636 new_class->instance_size = 0;
637 new_meta_class->instance_size = sizeof (struct objc_class);
643 objc_registerClassPair (Class class_)
648 if ((! CLS_ISCLASS (class_)) || (! CLS_IS_IN_CONSTRUCTION (class_)))
651 if ((! CLS_ISMETA (class_->class_pointer)) || (! CLS_IS_IN_CONSTRUCTION (class_->class_pointer)))
654 objc_mutex_lock (__objc_runtime_mutex);
656 if (objc_getClass (class_->name))
658 objc_mutex_unlock (__objc_runtime_mutex);
662 CLS_SET_NOT_IN_CONSTRUCTION (class_);
663 CLS_SET_NOT_IN_CONSTRUCTION (class_->class_pointer);
665 __objc_init_class (class_);
667 /* Resolve class links immediately. No point in waiting. */
668 __objc_resolve_class_links ();
670 objc_mutex_unlock (__objc_runtime_mutex);
674 objc_disposeClassPair (Class class_)
679 if ((! CLS_ISCLASS (class_)) || (! CLS_IS_IN_CONSTRUCTION (class_)))
682 if ((! CLS_ISMETA (class_->class_pointer)) || (! CLS_IS_IN_CONSTRUCTION (class_->class_pointer)))
685 /* Undo any class_addIvar(). */
689 for (i = 0; i < class_->ivars->ivar_count; i++)
691 struct objc_ivar *ivar = &(class_->ivars->ivar_list[i]);
693 objc_free ((char *)ivar->ivar_name);
694 objc_free ((char *)ivar->ivar_type);
697 objc_free (class_->ivars);
700 /* Undo any class_addMethod(). */
703 struct objc_method_list *list = class_->methods;
707 struct objc_method_list *next = list->method_next;
709 for (i = 0; i < list->method_count; i++)
711 struct objc_method *method = &(list->method_list[i]);
713 objc_free ((char *)method->method_name);
714 objc_free ((char *)method->method_types);
722 /* Undo any class_addProtocol(). */
723 if (class_->protocols)
725 struct objc_protocol_list *list = class_->protocols;
728 struct objc_protocol_list *next = list->next;
735 /* Undo any class_addMethod() on the meta-class. */
736 if (class_->class_pointer->methods)
738 struct objc_method_list *list = class_->class_pointer->methods;
742 struct objc_method_list *next = list->method_next;
744 for (i = 0; i < list->method_count; i++)
746 struct objc_method *method = &(list->method_list[i]);
748 objc_free ((char *)method->method_name);
749 objc_free ((char *)method->method_types);
757 /* Undo objc_allocateClassPair(). */
758 objc_free ((char *)(class_->name));
759 objc_free (class_->class_pointer);
763 /* Traditional GNU Objective-C Runtime API. */
764 /* Get the class object for the class named NAME. If NAME does not
765 identify a known class, the hook _objc_lookup_class is called. If
766 this fails, nil is returned. */
768 objc_lookup_class (const char *name)
770 return objc_getClass (name);
773 /* Traditional GNU Objective-C Runtime API. Important: this method is
774 called automatically by the compiler while messaging (if using the
775 traditional ABI), so it is worth keeping it fast; don't make it
776 just a wrapper around objc_getClass(). */
777 /* Note that this is roughly equivalent to objc_getRequiredClass(). */
778 /* Get the class object for the class named NAME. If NAME does not
779 identify a known class, the hook _objc_lookup_class is called. If
780 this fails, an error message is issued and the system aborts. */
782 objc_get_class (const char *name)
786 class = class_table_get_safe (name);
791 if (__objc_get_unknown_class_handler)
792 class = (*__objc_get_unknown_class_handler) (name);
794 if ((!class) && _objc_lookup_class)
795 class = (*_objc_lookup_class) (name);
800 _objc_abort ("objc runtime: cannot find class %s\n", name);
806 objc_get_meta_class (const char *name)
808 return objc_get_class (name)->class_pointer;
811 /* This function provides a way to enumerate all the classes in the
812 executable. Pass *ENUM_STATE == NULL to start the enumeration. The
813 function will return 0 when there are no more classes.
817 while ((class = objc_next_class (&es)))
818 ... do something with class;
821 objc_next_class (void **enum_state)
825 objc_mutex_lock (__objc_runtime_mutex);
827 /* Make sure the table is there. */
828 assert (__class_table_lock);
830 class = class_table_next ((struct class_table_enumerator **) enum_state);
832 objc_mutex_unlock (__objc_runtime_mutex);
837 /* This is used when the implementation of a method changes. It goes
838 through all classes, looking for the ones that have these methods
839 (either method_a or method_b; method_b can be NULL), and reloads
840 the implementation for these. You should call this with the
841 runtime mutex already locked. */
843 __objc_update_classes_with_methods (struct objc_method *method_a, struct objc_method *method_b)
847 /* Iterate over all classes. */
848 for (hash = 0; hash < CLASS_TABLE_SIZE; hash++)
850 class_node_ptr node = class_table_array[hash];
854 /* Iterate over all methods in the class. */
855 Class class = node->pointer;
856 struct objc_method_list * method_list = class->methods;
862 for (i = 0; i < method_list->method_count; ++i)
864 struct objc_method *method = &method_list->method_list[i];
866 /* If the method is one of the ones we are looking
867 for, update the implementation. */
868 if (method == method_a)
869 sarray_at_put_safe (class->dtable,
870 (sidx) method_a->method_name->sel_id,
871 method_a->method_imp);
873 if (method == method_b)
875 if (method_b != NULL)
876 sarray_at_put_safe (class->dtable,
877 (sidx) method_b->method_name->sel_id,
878 method_b->method_imp);
882 method_list = method_list->method_next;
889 /* Resolve super/subclass links for all classes. The only thing we
890 can be sure of is that the class_pointer for class objects point to
891 the right meta class objects. */
893 __objc_resolve_class_links (void)
895 struct class_table_enumerator *es = NULL;
896 Class object_class = objc_get_class ("Object");
899 assert (object_class);
901 objc_mutex_lock (__objc_runtime_mutex);
903 /* Assign subclass links. */
904 while ((class1 = class_table_next (&es)))
906 /* Make sure we have what we think we have. */
907 assert (CLS_ISCLASS (class1));
908 assert (CLS_ISMETA (class1->class_pointer));
910 /* The class_pointer of all meta classes point to Object's meta
912 class1->class_pointer->class_pointer = object_class->class_pointer;
914 if (! CLS_ISRESOLV (class1))
916 CLS_SETRESOLV (class1);
917 CLS_SETRESOLV (class1->class_pointer);
919 if (class1->super_class)
922 = objc_get_class ((char *) class1->super_class);
924 assert (a_super_class);
926 DEBUG_PRINTF ("making class connections for: %s\n",
929 /* Assign subclass links for superclass. */
930 class1->sibling_class = a_super_class->subclass_list;
931 a_super_class->subclass_list = class1;
933 /* Assign subclass links for meta class of superclass. */
934 if (a_super_class->class_pointer)
936 class1->class_pointer->sibling_class
937 = a_super_class->class_pointer->subclass_list;
938 a_super_class->class_pointer->subclass_list
939 = class1->class_pointer;
942 else /* A root class, make its meta object be a subclass of
945 class1->class_pointer->sibling_class
946 = object_class->subclass_list;
947 object_class->subclass_list = class1->class_pointer;
952 /* Assign superclass links. */
954 while ((class1 = class_table_next (&es)))
957 for (sub_class = class1->subclass_list; sub_class;
958 sub_class = sub_class->sibling_class)
960 sub_class->super_class = class1;
961 if (CLS_ISCLASS (sub_class))
962 sub_class->class_pointer->super_class = class1->class_pointer;
966 objc_mutex_unlock (__objc_runtime_mutex);
970 class_getName (Class class_)
979 class_isMetaClass (Class class_)
981 /* CLS_ISMETA includes the check for Nil class_. */
982 return CLS_ISMETA (class_);
985 /* Even inside libobjc it may be worth using class_getSuperclass
986 instead of accessing class_->super_class directly because it
987 resolves the class links if needed. If you access
988 class_->super_class directly, make sure to deal with the situation
989 where the class is not resolved yet! */
991 class_getSuperclass (Class class_)
996 /* Classes that are in construction are not resolved and can not be
998 if (CLS_IS_IN_CONSTRUCTION (class_))
1001 /* If the class is not resolved yet, super_class would point to a
1002 string (the name of the super class) as opposed to the actual
1003 super class. In that case, we need to resolve the class links
1004 before we can return super_class. */
1005 if (! CLS_ISRESOLV (class_))
1006 __objc_resolve_class_links ();
1008 return class_->super_class;
1012 class_getVersion (Class class_)
1017 return (int)(class_->version);
1021 class_setVersion (Class class_, int version)
1026 class_->version = version;
1030 class_getInstanceSize (Class class_)
1035 return class_->instance_size;
1038 #define CLASSOF(c) ((c)->class_pointer)
1041 class_pose_as (Class impostor, Class super_class)
1043 if (! CLS_ISRESOLV (impostor))
1044 __objc_resolve_class_links ();
1048 assert (super_class);
1049 assert (impostor->super_class == super_class);
1050 assert (CLS_ISCLASS (impostor));
1051 assert (CLS_ISCLASS (super_class));
1052 assert (impostor->instance_size == super_class->instance_size);
1055 Class *subclass = &(super_class->subclass_list);
1057 /* Move subclasses of super_class to impostor. */
1060 Class nextSub = (*subclass)->sibling_class;
1062 if (*subclass != impostor)
1064 Class sub = *subclass;
1067 sub->sibling_class = impostor->subclass_list;
1068 sub->super_class = impostor;
1069 impostor->subclass_list = sub;
1071 /* It will happen that SUB is not a class object if it is
1072 the top of the meta class hierarchy chain (root
1073 meta-class objects inherit their class object). If
1074 that is the case... don't mess with the meta-meta
1076 if (CLS_ISCLASS (sub))
1079 CLASSOF (sub)->sibling_class =
1080 CLASSOF (impostor)->subclass_list;
1081 CLASSOF (sub)->super_class = CLASSOF (impostor);
1082 CLASSOF (impostor)->subclass_list = CLASSOF (sub);
1086 *subclass = nextSub;
1089 /* Set subclasses of superclass to be impostor only. */
1090 super_class->subclass_list = impostor;
1091 CLASSOF (super_class)->subclass_list = CLASSOF (impostor);
1093 /* Set impostor to have no sibling classes. */
1094 impostor->sibling_class = 0;
1095 CLASSOF (impostor)->sibling_class = 0;
1098 /* Check relationship of impostor and super_class is kept. */
1099 assert (impostor->super_class == super_class);
1100 assert (CLASSOF (impostor)->super_class == CLASSOF (super_class));
1102 /* This is how to update the lookup table. Regardless of what the
1103 keys of the hashtable is, change all values that are superclass
1106 objc_mutex_lock (__objc_runtime_mutex);
1108 class_table_replace (super_class, impostor);
1110 objc_mutex_unlock (__objc_runtime_mutex);
1112 /* Next, we update the dispatch tables... */
1113 __objc_update_dispatch_table_for_class (CLASSOF (impostor));
1114 __objc_update_dispatch_table_for_class (impostor);