Java tutorial
/** * Copyright (C) 2011 the original author or authors. * See the notice.md file distributed with this work for additional * information regarding copyright ownership. * * Licensed 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.renyan.leveldb.impl; import com.google.common.base.Preconditions; import com.google.common.base.Throwables; import com.google.common.io.Closeables; import java.io.File; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.channels.FileChannel; import java.nio.channels.FileLock; import static java.lang.String.format; public class DbLock { private final File lockFile; private final FileChannel channel; private final FileLock lock; public DbLock(File lockFile) throws IOException { Preconditions.checkNotNull(lockFile, "lockFile is null"); this.lockFile = lockFile; // open and lock the file channel = new RandomAccessFile(lockFile, "rw").getChannel(); try { lock = channel.tryLock(); } catch (IOException e) { Closeables.closeQuietly(channel); throw e; } if (lock == null) { throw new IOException(format("Unable to acquire lock on '%s'", lockFile.getAbsolutePath())); } } public boolean isValid() { return lock.isValid(); } public void release() { try { lock.release(); } catch (IOException e) { Throwables.propagate(e); } finally { Closeables.closeQuietly(channel); } } @Override public String toString() { final StringBuilder sb = new StringBuilder(); sb.append("DbLock"); sb.append("{lockFile=").append(lockFile); sb.append(", lock=").append(lock); sb.append('}'); return sb.toString(); } }