Index: src/libcfa/concurrency/kernel
===================================================================
--- src/libcfa/concurrency/kernel	(revision 348006f9bbb24c9257fa8be8d10695e6da14597d)
+++ src/libcfa/concurrency/kernel	(revision 1e4f05e68a0cc389a37c3f17133c3feb44b2bc9b)
@@ -30,4 +30,13 @@
 void lock( spinlock * );
 void unlock( spinlock * );
+
+struct signal_once {
+	volatile bool condition;
+	struct spinlock lock;
+	struct simple_thread_list blocked;
+};
+
+void ?{}(signal_once * this);
+void ^?{}(signal_once * this);
 
 void wait( signal_once * );