Index: src/org/jruby/ext/Generator.java
===================================================================
--- src/org/jruby/ext/Generator.java	(Revision 4953)
+++ src/org/jruby/ext/Generator.java	(Arbeitskopie)
@@ -210,7 +210,10 @@
             } else {
                 proc.call(new IRubyObject[]{gen});
             }
-            end = true;
+            synchronized (mutex) {
+                end = true;
+                mutex.notifyAll();
+            }
         }
     }