FileChannel.lock() question

Question

Hi
(code below)
According to the documentation on the FileLock.lock() method...
" An invocation of this method will block until the region can be locked, this channel is closed, or the invoking thread is interrupted, whichever comes first. "
So I would expect whichever thread that gets executed second to wait patiently until a lock on the (0,23) portion of the file can be obtained.
However, I get a "Java.nio.channels.OverlappingFileLockException" when the second thread attemps to acquire a lock on the (0,23) portion of the file.
How can I get a thread to wait until it can acquire a lock on the (0,23) portion of the file can be obtained... and then acquire the lock???
Thanks for your help...
public static void main(String[] args) {
  try{
    final File f = new File("<filename>");
    final RandomAccessFile raf = new RandomAccessFile(f, "rw");
    final FileChannel channel = raf.getChannel();
    class tobj implements Runnable {
      public void run(){
        try{
          channel.lock(0, 23, true);
          System.out.println(Thread.currentThread() + " is done");
        catch(Exception e){
          System.out.println(e);
    new Thread(new tobj()).start();
    new Thread(new tobj()).start();
    //raf.close();
  catch(Exception e){
    System.out.println(e);
}

Answer 1

I have a flat file that is accessed by multiple threads. Speed is of utmost importance. If thread A wants to read bytes 1-50 and thread B wants to overwrite bytes 100 - 150, the program should allow the threads to do this concurrently as the threads will not affect each other. But if thread A wants to overwrite bytes 1 - 50 then immediately after thread B wants to read the same area (bytes 1 - 50), then thread B should wait until a is finished with that area of the file.
Multiple threads should be able to read from the same area at the same time.
But when a thread wants to write to an area of a file, it should have sole control of that area until it is finished.
Any ideas..
I really appreciate you help..
I really appreciate you help..