Index: src/libcfa/concurrency/kernel
===================================================================
--- src/libcfa/concurrency/kernel	(revision 348006f9bbb24c9257fa8be8d10695e6da14597d)
+++ src/libcfa/concurrency/kernel	(revision d9c8a597c64732b01c6014a27959e095f47857ef)
@@ -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 * );