Clean up the low memory profile. Now passes all GNUstep-base and EtoileFoundation tests, just like the default profileand uses 5-10% less (total) RAM in GORM. Worth benchmarking to see how much performance this costs.

Updated the release announcement.

ANNOUNCE

@@ -6,8 +6,18 @@ libobjc2).  This runtime was designed to support the features of Objective-C 2
 for use with GNUstep and other Objective-C programs.  Highlights of this
 release include:
 
-- Support for the associated reference APIs introduced with OS X 10.6
+- Support for the associated reference APIs introduced with OS X 10.6.  This
-- Better hiding of local symbols
+  allows storing arbitrary objects associated with another object.
+- Concurrent, thread-safe, +initialize.  The runtime will now send +initialize
+  messages to different classes concurrently in multiple threads, but still
+  ensures that no class receives another message until it has returned from
+  +initialize.  Exceptions can now safely propagate out of +initialize methods.
+- Better hiding of local symbols.  Now the internal runtime functions are not
+  visible from outside of the runtime.
+- Dispatch table updates have been improved.  Category loading no longer
+  triggers dtable creation and partial dtable updates are faster.  
+- Improvements to the low memory profile.  Uses 5-10% less memory running Gorm,
+  and now passes the entire GNUstep and EtoileFoundation test suites.
 
 You may obtain the code for this release from subversion at the following
 subversion branch:

dtable.c

@@ -1,3 +1,4 @@
+#define __BSD_VISIBLE 1
 #include <stdio.h>
 #include <stdlib.h>
 #include "objc/runtime.h"
@@ -165,27 +166,9 @@ static void insert_slot(dtable_t dtable, struct objc_slot *slot, uint32_t idx)
 	dtable->slots[dtable->slot_count++].idx = idx;
 }
 
-static void update_dtable(dtable_t dtable)
+static void add_slot_to_dtable(uint32_t idx, dtable_t dtable, uint32_t
+		old_slot_count, struct objc_method *m, Class cls)
 {
-	Class cls = dtable->cls;
-
-	if (NULL == cls->methods) { return; }
-
-	SparseArray *methods = SparseArrayNewWithDepth(dtable_depth);
-	collectMethodsForMethodListToSparseArray((void*)cls->methods, methods, YES);
-
-	if (NULL == dtable->slots)
-	{
-		dtable->slots = calloc(sizeof(struct slots_list), 16);
-		dtable->slot_size = 16;
-	}
-
-	uint32_t old_slot_count = dtable->slot_count;
-	struct objc_method *m;
-	uint32_t idx = 0;
-	while ((m = SparseArrayNext(methods, &idx)))
-	{
-		uint32_t idx = m->selector->index;
 		struct slots_list *s = find_slot(idx, dtable->slots, old_slot_count);
 		if (NULL != s)
 		{
@@ -206,6 +189,31 @@ static void update_dtable(dtable_t dtable)
 			}
 		}
 }
+static void update_dtable(dtable_t dtable)
+{
+	Class cls = dtable->cls;
+
+	if (NULL == cls->methods) { return; }
+
+	SparseArray *methods = SparseArrayNewWithDepth(dtable_depth);
+	collectMethodsForMethodListToSparseArray((void*)cls->methods, methods, YES);
+
+	if (NULL == dtable->slots)
+	{
+		dtable->slots = calloc(sizeof(struct slots_list), 16);
+		dtable->slot_size = 16;
+	}
+
+	uint32_t old_slot_count = dtable->slot_count;
+	struct objc_method *m;
+	uint32_t idx = 0;
+	while ((m = SparseArrayNext(methods, &idx)))
+	{
+		add_slot_to_dtable(m->selector->index, dtable, old_slot_count, m, cls);
+#ifdef TYPE_DEPENDENT_DISPATCH
+		add_slot_to_dtable(get_untyped_idx(m->selector), dtable, old_slot_count, m, cls);
+#endif
+	}
 	mergesort(dtable->slots, dtable->slot_count, sizeof(struct slots_list),
 			slot_cmp);
 	SparseArrayDestroy(methods);
@@ -223,6 +231,11 @@ PRIVATE void objc_update_dtable_for_class(Class cls)
 	update_dtable(dtable);
 
 }
+PRIVATE void add_method_list_to_class(Class cls,
+                                      struct objc_method_list *list)
+{
+	objc_update_dtable_for_class(cls);
+}
 
 PRIVATE struct objc_slot* objc_dtable_lookup(dtable_t dtable, uint32_t uid)
 {
@@ -246,17 +259,21 @@ PRIVATE struct objc_slot* objc_dtable_lookup(dtable_t dtable, uint32_t uid)
 		slot = s->slot;
 		int i = HASH_UID(uid);
 		volatile struct cache_line *cache = &dtable->cache[i];
-		cache->idx = 0;
+		// Simplified multiword atomic exchange.  First we write a value that
+		// is an invalid but recognisable UID and then a memory barrier.  Then
+		// we complete the update and set the index pointer if and only if
+		// there have been no other modifications in the meantime
+		cache->idx = -uid;
+		__sync_synchronize();
 		cache->version = slot->version;
 		cache->slot = slot;
-		__sync_synchronize();
+		__sync_bool_compare_and_swap(&cache->idx, -uid, uid);
-		cache->idx = uid;
 		return slot;
 	}
 
 	if (NULL != dtable->cls->super_class)
 	{
-		return objc_dtable_lookup(dtable->cls->super_class->dtable, uid);
+		return objc_dtable_lookup(dtable_for_class(dtable->cls->super_class), uid);
 	}
 	return NULL;
 }
@@ -274,7 +291,7 @@ PRIVATE void free_dtable(dtable_t dtable)
 	{
 		free(dtable->slots);
 	}
-	DESTROY_LOCK(dtable->lock);
+	DESTROY_LOCK(&dtable->lock);
 	free(dtable);
 }
 
@@ -585,13 +602,6 @@ PRIVATE void objc_send_initialize(id object)
 	// If this class is already initialized (e.g. in another thread), give up.
 	if (objc_test_class_flag(class, objc_class_flag_initialized)) { return; }
 
-	// Grab a lock to make sure we are only sending one +initialize message at
-	// once.  
-	//
-	// NOTE: Ideally, we would actually lock on the class object using
-	// objc_sync_enter().  This should be fixed once sync.m contains a (fast)
-	// special case for classes.
-
 	// Make sure that the class is resolved.
 	objc_resolve_class(class);