Examples of org.exist.storage.lock.FileLock

org.exist.storage.lock.FileLock

Cooperative inter-process file locking, used to synchronize access to database files across processes, i.e. across different Java VMs or separate database instances within one VM. This is similar to the native file locks provided by Java NIO. However, the NIO implementation has various problems. Among other things, we observed that locks were not properly released on WinXP. FileLock implements a cooperative approach. The class attempts to write a lock file at the specified location. Every lock file stores 1) a magic word to make sure that the file was really written by eXist, 2) a heartbeat timestamp. The procedure for acquiring the lock in {@link #tryLock()} is as follows:If a lock file does already exist in the specified location, we check its heartbeat timestamp. If the timestamp is more than {@link #HEARTBEAT} milliseconds in the past, we assumethat the lock is stale and its owner process has died. The lock file is removed and we create a new one. If the heartbeat indicates that the owner process is still alive, the lock attempt is aborted and {@link #tryLock()} returns false.Otherwise, we create a new lock file and start a daemon thread to periodically update the lock file's heart-beat value. @author Wolfgang Meier

            {journalSizeLimit = sizeOpt.intValue() * 1024 * 1024;}
    }


    public void initialize() throws EXistException, ReadOnlyException {
        final File lck = new File(dir, LCK_FILE);
        fileLock = new FileLock(pool, lck.getAbsolutePath());
        boolean locked = fileLock.tryLock();
        if (!locked) {
            final String lastHeartbeat =
                DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM)
                    .format(fileLock.getLastHeartbeat());

            LOG.info("Cannot write to data directory: " + dir.getAbsolutePath() + ". Switching to read-only mode.");
            return false;
        }


        // try to acquire lock on the data dir
        dataLock = new FileLock(this, dir, "dbx_dir.lck");


        try {
            final boolean locked = dataLock.tryLock();
            if(!locked) {
                throw new EXistException("The database directory seems to be locked by another " +

Examples of org.exist.storage.lock.FileLock

Related Classes of org.exist.storage.lock.FileLock