com.iflytek.spider.util.LockUtil.java Source code

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Here is the source code for com.iflytek.spider.util.LockUtil.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.iflytek.spider.util;

import java.io.IOException;

import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

/**
 * Utility methods for handling application-level locking.
 * 
 * @author Andrzej Bialecki
 */
public class LockUtil {

    /**
     * Create a lock file.
     * @param fs filesystem
     * @param lockFile name of the lock file
     * @param accept if true, and the target file exists, consider it valid. If false
     * and the target file exists, throw an IOException.
     * @throws IOException if accept is false, and the target file already exists,
     * or if it's a directory.
     */
    public static void createLockFile(FileSystem fs, Path lockFile, boolean accept) throws IOException {
        if (fs.exists(lockFile)) {
            if (!accept)
                throw new IOException("lock file " + lockFile + " already exists.");
            if (fs.getFileStatus(lockFile).isDir())
                throw new IOException("lock file " + lockFile + " already exists and is a directory.");
            // do nothing - the file already exists.
        } else {
            // make sure parents exist
            fs.mkdirs(lockFile.getParent());
            fs.createNewFile(lockFile);
        }
    }

    /**
     * Remove lock file. NOTE: applications enforce the semantics of this file -
     * this method simply removes any file with a given name.
     * @param fs filesystem
     * @param lockFile lock file name
     * @return false, if the lock file doesn't exist. True, if it existed and was
     * successfully removed.
     * @throws IOException if lock file exists but it is a directory.
     */
    public static boolean removeLockFile(FileSystem fs, Path lockFile) throws IOException {
        if (!fs.exists(lockFile))
            return false;
        if (fs.getFileStatus(lockFile).isDir())
            throw new IOException("lock file " + lockFile + " exists but is a directory!");
        return fs.delete(lockFile, false);
    }
}