FileLock in Java doesn't work in Docker mount volume

Question

In my situation, some web configuration files are shared through mount folder in Docker. In same cases we want to modify these files concurrently. That's why I want to use lock to make sure file is being modified once at the same time. But I found flock is not working in Docker. Does it not supported?

 public void modifyFile() {

    try {
        File file = new File("/tmp/fileToLock.dat");

        // Creates a random access file stream to read from, and optionally to write to
        FileChannel channel = new RandomAccessFile(file, "rw").getChannel();

        // Acquire an exclusive lock on this channel's file (blocks until lock can be retrieved)
        FileLock lock = null;

        // Attempts to acquire an exclusive lock on this channel's file (returns null or throws
        // an exception if the file is already locked.
        try {
            lock = channel.tryLock();
            if (null != lock) {
                List<String> fileToString = FileUtils.readLines(file, StandardCharsets.UTF_8);
                long l = 0l;
                if (null != fileToString && fileToString.size() > 0) {
                    l = Long.valueOf(fileToString.get(fileToString.size() - 1));
                }
                l++;
                FileUtils.writeStringToFile(file, String.valueOf(l) + "\r\n", StandardCharsets.UTF_8, true);
            }
        } catch (OverlappingFileLockException e) {
            // thrown when an attempt is made to acquire a lock on a a file that overlaps
            // a region already locked by the same JVM or when another thread is already
            // waiting to lock an overlapping region of the same file
            System.out.println("Overlapping File Lock Error: " + e.getMessage());
            channel.close();
        }

        // release the lock
        if (null != lock) {
            lock.release();
        }
        // close the channel
        channel.close();

    } catch (IOException e) {
        System.out.println("I/O Error: " + e.getMessage());
    }

}

Answer 1

In the end, I just leave any lock implementation for file without any Redis lock thing.