Dumping the SelectionKeys is a non-blocking action.

jetty-io/src/main/java/org/eclipse/jetty/io/ManagedSelector.java

@@ -455,7 +455,7 @@ public class ManagedSelector extends ContainerLifeCycle implements Dumpable
         }
     }
 
-    private class DumpKeys implements Runnable
+    private class DumpKeys extends NonBlockingAction
     {
         private final CountDownLatch latch = new CountDownLatch(1);
         private final List<Object> _dumps;