fix a race condition bug when dispatching and resolving a method at t…

…he same time

git-svn-id: http://svn.macosforge.org/repository/ruby/MacRuby/trunk@5234 23306eb0-4c56-4727-a40e-e92c0eb68959

dispatcher.cpp

@@ -673,13 +673,26 @@ rb_vm_dispatch(void *_vm, struct mcache *cache, VALUE top, VALUE self,
 	    // Does the receiver implements -forwardInvocation:?
 	    if ((opt & DISPATCH_SUPER) == 0
 		    && rb_objc_supports_forwarding(self, sel)) {
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED < 1070
+		// In earlier versions of the Objective-C runtime, there seems
+		// to be a bug where class_getInstanceMethod isn't atomic,
+		// and might return NULL while at the exact same time another
+		// thread registers the related method.
+		// As a work-around, we double-check if the method still does
+		// not exist here. If he does, we can dispatch it properly.
+		method = class_getInstanceMethod(klass, sel);
+		if (method != NULL) {
+		    goto recache2;
+		}
+#endif
 		fill_ocache(cache, self, klass, (IMP)objc_msgSend, sel, NULL,
 			argc);
 		goto dispatch;
 	    }
 
 	    // Let's see if are not trying to call a Ruby method that accepts
-	    // a regular argument then a optional Hash argument, to be
+	    // a regular argument then an optional Hash argument, to be
 	    // compatible with the Ruby specification.
 	    const char *selname = (const char *)sel;
 	    size_t selname_len = strlen(selname);