org.eclipse.rdf4j.sail.nativerdf.TxnStatusFile Maven / Gradle / Ivy

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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/
package org.eclipse.rdf4j.sail.nativerdf;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

import org.eclipse.rdf4j.common.io.NioFile;

/**
 * Writes transaction statuses to a file.
 */
class TxnStatusFile {

	public static enum TxnStatus {

		/**
		 * No active transaction. This occurs if no transaction has been started yet, or if all transactions
		 * have been committed or rolled back.
		 */
		NONE,

		/**
		 * A transaction has been started, but was not yet committed or rolled back.
		 */
		ACTIVE,

		/**
		 * A transaction is being committed.
		 */
		COMMITTING,

		/**
		 * A transaction is being rolled back.
		 */
		ROLLING_BACK,

		/**
		 * The transaction status is unknown.
		 */
		UNKNOWN;
	}

	private static final Charset US_ASCII = Charset.forName("US-ASCII");

	/**
	 * The name of the transaction status file.
	 */
	public static final String FILE_NAME = "txn-status";

	private final NioFile nioFile;

	/**
	 * Creates a new transaction status file. New files are initialized with {@link TxnStatus#NONE}.
	 * 
	 * @param dataDir
	 *        The directory for the transaction status file.
	 * @throws IOException
	 *         If the file did not yet exist and could not be written to.
	 */
	public TxnStatusFile(File dataDir)
		throws IOException
	{
		File statusFile = new File(dataDir, FILE_NAME);
		nioFile = new NioFile(statusFile, "rwd");

		if (nioFile.size() == 0) {
			setTxnStatus(TxnStatus.NONE);
		}
	}

	public void close()
		throws IOException
	{
		nioFile.close();
	}

	/**
	 * Writes the specified transaction status to file.
	 * 
	 * @param txnStatus
	 *        The transaction status to write.
	 * @throws IOException
	 *         If the transaction status could not be written to file.
	 */
	public void setTxnStatus(TxnStatus txnStatus)
		throws IOException
	{
		byte[] bytes = txnStatus.name().getBytes(US_ASCII);
		nioFile.truncate(bytes.length);
		nioFile.writeBytes(bytes, 0);
	}

	/**
	 * Reads the transaction status from file.
	 * 
	 * @return The read transaction status, or {@link TxnStatus#UNKNOWN} when the file contains an
	 *         unrecognized status string.
	 * @throws IOException
	 *         If the transaction status file could not be read.
	 */
	public TxnStatus getTxnStatus()
		throws IOException
	{
		byte[] bytes = nioFile.readBytes(0, (int)nioFile.size());
		String s = new String(bytes, US_ASCII);
		try {
			return TxnStatus.valueOf(s);
		}
		catch (IllegalArgumentException e) {
			// use platform encoding for backwards compatibility with versions
			// older than 2.6.6:
			s = new String(bytes);
			try {
				return TxnStatus.valueOf(s);
			}
			catch (IllegalArgumentException e2) {
				return TxnStatus.UNKNOWN;
			}
		}
	}
}