| /** |
| * 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.datanode.fsdataset; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| import java.util.Iterator; |
| |
| /** |
| * Rolling logs consist of a current log and a set of previous logs. |
| * |
| * The implementation should support a single appender and multiple readers. |
| */ |
| public interface RollingLogs { |
| /** |
| * To iterate the lines of the logs. |
| */ |
| public interface LineIterator extends Iterator<String>, Closeable { |
| /** Is the iterator iterating the previous? */ |
| public boolean isPrevious(); |
| } |
| |
| /** |
| * To append text to the logs. |
| */ |
| public interface Appender extends Appendable, Closeable { |
| } |
| |
| /** |
| * Create an iterator to iterate the lines in the logs. |
| * |
| * @param skipPrevious Should it skip reading the previous log? |
| * @return a new iterator. |
| */ |
| public LineIterator iterator(boolean skipPrevious) throws IOException; |
| |
| /** |
| * @return the only appender to append text to the logs. |
| * The same object is returned if it is invoked multiple times. |
| */ |
| public Appender appender(); |
| |
| /** |
| * Roll current to previous. |
| * |
| * @return true if the rolling succeeded. |
| * When it returns false, it is not equivalent to an error. |
| * It means that the rolling cannot be performed at the moment, |
| * e.g. the logs are being read. |
| */ |
| public boolean roll() throws IOException; |
| } |