FileMaker.java

/*
 *   $Id$
 *
 *   Copyright 2009 Glencoe Software, Inc. All rights reserved.
 *   Use is subject to license terms supplied in LICENSE.txt
 */

package ome.services.blitz.repo;

import java.io.EOFException;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileLock;
import java.util.Date;

import ome.conditions.InternalException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Utility class for creating and cleaning up a repository lock file. After
 * {@link #init(String) initialization}, a call to {@link #getLine()} will
 * either return the UUID of the repository or null. If null, then
 * {@link #writeLine(String)} can be used to assert that this repository is to
 * be named according to the string.
 */
public class FileMaker {

    private final static Logger log = LoggerFactory.getLogger(FileMaker.class);

    private final Object[] mutex = new Object[0];

    private final String repoDir;

    private/* final */String dbUuid;

    private File repoUuidFile, dotLockFile;

    private RandomAccessFile repoUuidRaf, dotLockRaf;

    private FileLock lock;

    public FileMaker(String repoDir) {
        this.repoDir = repoDir;
    }

    public String getDir() {
        return this.repoDir;
    }

    public boolean needsInit() {
        synchronized (mutex) {
            return this.dbUuid == null;
        }
    }

    /**
     * @param dbUuid
     * @throws Exception
     */
    public void init(String dbUuid) throws Exception {
        synchronized (mutex) {

            if (this.dbUuid != null) {
                throw new InternalException("Already initialized");
            }

            this.dbUuid = dbUuid;
            File mountDir = new File(repoDir);
            File omeroDir = new File(mountDir, ".omero");
            File repoCfg = new File(omeroDir, "repository");
            File uuidDir = new File(repoCfg, dbUuid);
            if (!uuidDir.exists()) {
                uuidDir.mkdirs();
                log.info("Creating " + uuidDir);
            }

            repoUuidFile = new File(uuidDir, "repo_uuid");
            dotLockFile = new File(uuidDir, ".lock");
            repoUuidRaf = new RandomAccessFile(repoUuidFile, "rw");
            dotLockRaf = new RandomAccessFile(dotLockFile, "rw");

        }
    }

    public String getLine() throws Exception {
        synchronized (mutex) {

            if (dbUuid == null) {
                throw new InternalException("Not initialized");
            }

            lock = dotLockRaf.getChannel().lock();
            dotLockRaf.seek(0);
            dotLockRaf.writeUTF(new Date().toString());

            String line = null;
            try {
                repoUuidRaf.seek(0);
                line = repoUuidRaf.readUTF();
            } catch (EOFException eof) {
                // pass
            }
            return line;
        }
    }

    public void writeLine(String line) throws Exception {

        synchronized (mutex) {

            if (dbUuid == null) {
                throw new InternalException("Not initialized");
            }

            repoUuidRaf.seek(0);
            repoUuidRaf.writeUTF(line);
        }
    }

    public void close() {

        synchronized (mutex) {

            if (dbUuid == null) {
                return;
            }

            try {
                if (lock != null) {
                    lock.release();
                }
            } catch (IOException e) {
                log.warn("Failed to release lock");
            }

            try {
                if (repoUuidRaf != null) {
                    repoUuidRaf.close();
                }
            } catch (IOException e) {
                log.warn("Failed to close repo_uuid");
            }

            try {
                if (dotLockRaf != null) {
                    dotLockRaf.close();
                }
            } catch (IOException e) {
                log.warn("Failed to close .lock");
            }

            dbUuid = null;
            repoUuidFile = null;
            if (!dotLockFile.delete()) {
                log.warn("Failed to delete lock file: "
                        + dotLockFile.getAbsolutePath());
            }
            dotLockFile = null;
            repoUuidRaf = null;
            dotLockRaf = null;

        }
    }

}