com.alibaba.wasp.ZNodeClearer.java Source code

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Here is the source code for com.alibaba.wasp.ZNodeClearer.java

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/**
 * 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 com.alibaba.wasp;

import com.alibaba.wasp.zookeeper.MasterAddressTracker;
import com.alibaba.wasp.zookeeper.ZooKeeperWatcher;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.Abortable;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

/**
 * <p>
 * Contains a set of methods for the collaboration between the start/stop
 * scripts and the servers. It allows to delete immediately the znode when the
 * master or the entityGroups server crashes. The entityGroup server / master
 * writes a specific file when it starts / becomes main master. When they end
 * properly, they delete the file.
 * </p>
 * <p>
 * In the script, we check for the existence of these files when the program
 * ends. If they still exist we conclude that the server crashed, likely without
 * deleting their znode. To have a faster recovery we delete immediately the
 * znode.
 * </p>
 * <p>
 * The strategy depends on the server type. For a entityGroup server we store
 * the znode path in the file, and use it to delete it. for a master, as the
 * znode path constant whatever the server, we check its content to make sure
 * that the backup server is not now in charge.
 * </p>
 */
public class ZNodeClearer {
    public static final Log LOG = LogFactory.getLog(ZNodeClearer.class);

    private ZNodeClearer() {
    }

    /**
     * Logs the errors without failing on exception.
     */
    public static void writeMyEphemeralNodeOnDisk(String fileContent) {
        String fileName = ZNodeClearer.getMyEphemeralNodeFileName();

        if (fileName == null) {
            LOG.warn("No filename given to save the znode used, it won't be saved "
                    + "(Environment variable WASP_ZNODE_FILE is not set).");
            return;
        }

        FileWriter fstream;
        try {
            fstream = new FileWriter(fileName);
        } catch (IOException e) {
            LOG.warn("Can't write znode file " + fileName, e);
            return;
        }

        BufferedWriter out = new BufferedWriter(fstream);

        try {
            try {
                out.write(fileContent + "\n");
            } finally {
                try {
                    out.close();
                } finally {
                    fstream.close();
                }
            }
        } catch (IOException e) {
            LOG.warn("Can't write znode file " + fileName, e);
        }
    }

    /**
     * read the content of znode file, expects a single line.
     */
    public static String readMyEphemeralNodeOnDisk() throws IOException {
        String fileName = getMyEphemeralNodeFileName();
        if (fileName == null) {
            throw new IOException("No filename");
        }
        FileReader znodeFile = new FileReader(fileName);
        BufferedReader br = new BufferedReader(znodeFile);
        String file_content = br.readLine();
        br.close();
        return file_content;
    }

    /**
     * Get the name of the file used to store the znode contents
     */
    public static String getMyEphemeralNodeFileName() {
        return System.getenv().get("WASP_ZNODE_FILE");
    }

    /**
     * delete the znode file
     */
    public static void deleteMyEphemeralNodeOnDisk() {
        String fileName = getMyEphemeralNodeFileName();

        if (fileName != null) {
            new File(fileName).delete();
        }
    }

    /**
     * Delete the master znode if its content (ServerName string) is the same as
     * the one in the znode file. (env: HBASE_ZNODE_FILE).
     * 
     * @return true on successful deletion, false otherwise.
     */
    public static boolean clear(Configuration conf) {
        Configuration tempConf = new Configuration(conf);
        tempConf.setInt("zookeeper.recovery.retry", 0);

        ZooKeeperWatcher zkw;
        try {
            zkw = new ZooKeeperWatcher(tempConf, "clean znode for master", new Abortable() {
                @Override
                public void abort(String why, Throwable e) {
                }

                @Override
                public boolean isAborted() {
                    return false;
                }
            });
        } catch (IOException e) {
            LOG.warn("Can't connect to zookeeper to read the master znode", e);
            return false;
        }

        String znodeFileContent;
        try {
            znodeFileContent = ZNodeClearer.readMyEphemeralNodeOnDisk();
        } catch (IOException e) {
            LOG.warn("Can't read the content of the znode file", e);
            return false;
        }

        return MasterAddressTracker.deleteIfEquals(zkw, znodeFileContent);
    }
}