Merge pull request #21 from ngrewe/deadlock

Avoid deadlock in objc_send_initialize()

dtable.c

@@ -824,6 +824,13 @@ PRIVATE void objc_send_initialize(id object)
 		objc_send_initialize((id)class->super_class);
 	}
 
+	// Lock the runtime while we're creating dtables and before we acquire any
+	// other locks.  This prevents a lock-order reversal when
+	// dtable_for_class is called from something holding the runtime lock while
+	// we're still holding the initialize lock.  We should ensure that we never
+	// acquire the runtime lock after acquiring the initialize lock.
+	LOCK_RUNTIME();
+
 	// Superclass +initialize might possibly send a message to this class, in
 	// which case this method would be called again.  See NSObject and
 	// NSAutoreleasePool +initialize interaction in GNUstep.
@@ -831,19 +838,17 @@ PRIVATE void objc_send_initialize(id object)
 	{
 		// We know that initialization has started because the flag is set.
 		// Check that it's finished by grabbing the class lock.  This will be
-		// released once the class has been fully initialized
+		// released once the class has been fully initialized. The runtime
+		// lock needs to be released first to prevent a deadlock between the
+		// runtime lock and the class-specific lock.
+		UNLOCK_RUNTIME();
+
 		objc_sync_enter((id)meta);
 		objc_sync_exit((id)meta);
 		assert(dtable_for_class(class) != uninstalled_dtable);
 		return;
 	}
 
-	// Lock the runtime while we're creating dtables and before we acquire any
-	// other locks.  This prevents a lock-order reversal when 
-	// dtable_for_class is called from something holding the runtime lock while
-	// we're still holding the initialize lock.  We should ensure that we never
-	// acquire the runtime lock after acquiring the initialize lock.
-	LOCK_RUNTIME();
 	LOCK_OBJECT_FOR_SCOPE((id)meta);
 	LOCK(&initialize_lock);
 	if (objc_test_class_flag(class, objc_class_flag_initialized))