Demonstrate Java NIO file locking capability.

MultiThreadedWriteTest.java

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.InterruptedException;
import java.lang.Thread;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;

public class MultiThreadedWriteTest
{
  public static void main(final String[] args) throws Exception
  {
    if (args.length < 1) {
      System.out.println("Usage: MultiThreadedWriteTest /path/to/file");
      return;
    }
    final Thread t1 = new Thread(new Writer(new File(args[0])), "thread-1");
    final Thread t2 = new Thread(new Writer(new File(args[0])), "thread-2");
    t1.start();
    t2.start();
    t1.join();
    t2.join();
  }

  static class Writer implements Runnable
  {
    private final File file;

    public Writer(final File file) {
      this.file = file;
    }

    public void run() {
      FileChannel channel = null;
      FileLock lock = null;
      final ByteBuffer buffer = ByteBuffer.allocate(100);
      final String line = "Hello from thread " + Thread.currentThread().getName() + "\n";
      buffer.put(line.getBytes());
      buffer.flip();
      try {
        channel = new FileOutputStream(file).getChannel();
        int maxTries = 4;
        int count = 0;
        do {
          try {
            lock = channel.lock();
          } catch (OverlappingFileLockException e) {
            System.out.println(Thread.currentThread().getName() + " can't get file lock. Waiting 500ms.");
            Thread.sleep(500);
            count++;
          }
        } while (lock == null && count < maxTries);
        if (lock != null) {
          System.out.println(Thread.currentThread().getName() + " writing to " + file);
          channel.write(buffer);
        } else {
          System.out.println(Thread.currentThread().getName() + " giving up after " + count + " tries");
        }
      } catch (Exception e) {
        e.printStackTrace();
      } finally {
        if (lock != null) {
          try {
            lock.release();
          } catch (Exception e) {
            System.out.println("Failed releasing lock");
            e.printStackTrace();
          }
        }
        if (channel != null) {
          try {
            channel.close();
          } catch (IOException e) {
            System.out.println("Failed closing file channel");
            e.printStackTrace();
          }
        }
      }
    }
  }
}