Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.hdfs.server.namenode; import java.util.concurrent.Callable; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.hdfs.server.namenode.JournalSet.JournalAndStream; import org.apache.hadoop.hdfs.server.namenode.JournalSet.JournalClosure; /** * JournalSetWorker applies JournalClosure operation on JournalAndStream. It is * submitted as a task to an executor, the call method return the journal in * case of failure, so we can handle it outside. */ class JournalSetWorker implements Callable<JournalAndStream> { static final Log LOG = LogFactory.getLog(JournalSetWorker.class); private JournalAndStream jas; private JournalClosure closure; private String status; JournalSetWorker(JournalAndStream jas, JournalClosure closure, String status) { this.jas = jas; this.closure = closure; this.status = status; } @Override public JournalAndStream call() throws Exception { try { closure.apply(jas); } catch (Throwable t) { LOG.error("Error: " + status + " failed for (journal " + jas + ")", t); // pass it back to handle as a failed journal return jas; } // if the call was successful, just return null; return null; } }