001/** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.kahadb.util; 018 019import java.io.File; 020import java.io.IOException; 021import java.io.RandomAccessFile; 022import java.nio.channels.FileLock; 023import java.nio.channels.OverlappingFileLockException; 024import java.util.Date; 025 026/** 027 * Used to lock a File. 028 * 029 * @author chirino 030 */ 031public class LockFile { 032 033 private static final boolean DISABLE_FILE_LOCK = Boolean.getBoolean("java.nio.channels.FileLock.broken"); 034 final private File file; 035 036 private FileLock lock; 037 private RandomAccessFile readFile; 038 private int lockCounter; 039 private final boolean deleteOnUnlock; 040 041 public LockFile(File file, boolean deleteOnUnlock) { 042 this.file = file; 043 this.deleteOnUnlock = deleteOnUnlock; 044 } 045 046 /** 047 * @throws IOException 048 */ 049 synchronized public void lock() throws IOException { 050 if (DISABLE_FILE_LOCK) { 051 return; 052 } 053 054 if (lockCounter > 0) { 055 return; 056 } 057 058 IOHelper.mkdirs(file.getParentFile()); 059 synchronized (LockFile.class) { 060 if (System.getProperty(getVmLockKey()) != null) { 061 throw new IOException("File '" + file + "' could not be locked as lock is already held for this jvm."); 062 } 063 System.setProperty(getVmLockKey(), new Date().toString()); 064 } 065 try { 066 if (lock == null) { 067 readFile = new RandomAccessFile(file, "rw"); 068 IOException reason = null; 069 try { 070 lock = readFile.getChannel().tryLock(0, Math.max(1, readFile.getChannel().size()), false); 071 } catch (OverlappingFileLockException e) { 072 reason = IOExceptionSupport.create("File '" + file + "' could not be locked.", e); 073 } catch (IOException ioe) { 074 reason = ioe; 075 } 076 if (lock != null) { 077 lockCounter++; 078 System.setProperty(getVmLockKey(), new Date().toString()); 079 } else { 080 // new read file for next attempt 081 closeReadFile(); 082 if (reason != null) { 083 throw reason; 084 } 085 throw new IOException("File '" + file + "' could not be locked."); 086 } 087 088 } 089 } finally { 090 synchronized (LockFile.class) { 091 if (lock == null) { 092 System.getProperties().remove(getVmLockKey()); 093 } 094 } 095 } 096 } 097 098 /** 099 */ 100 public void unlock() { 101 if (DISABLE_FILE_LOCK) { 102 return; 103 } 104 105 lockCounter--; 106 if (lockCounter != 0) { 107 return; 108 } 109 110 // release the lock.. 111 if (lock != null) { 112 try { 113 lock.release(); 114 System.getProperties().remove(getVmLockKey()); 115 } catch (Throwable ignore) { 116 } 117 lock = null; 118 } 119 closeReadFile(); 120 121 if (deleteOnUnlock) { 122 file.delete(); 123 } 124 } 125 126 private String getVmLockKey() throws IOException { 127 return getClass().getName() + ".lock." + file.getCanonicalPath(); 128 } 129 130 private void closeReadFile() { 131 // close the file. 132 if (readFile != null) { 133 try { 134 readFile.close(); 135 } catch (Throwable ignore) { 136 } 137 readFile = null; 138 } 139 140 } 141 142}