#ROCKETMQ-340# improve code for avoid ClassCastException. (#210)

broker/src/main/java/org/apache/rocketmq/broker/latency/BrokerFastFailure.java

@@ -44,8 +44,10 @@ public class BrokerFastFailure {
 
     public static RequestTask castRunnable(final Runnable runnable) {
         try {
+            if (runnable instanceof FutureTaskExt) {
                 FutureTaskExt object = (FutureTaskExt) runnable;
                 return (RequestTask) object.getRunnable();
+            }
         } catch (Throwable e) {
             log.error(String.format("castRunnable exception, %s", runnable.getClass().getName()), e);
         }