!7

import java.nio.channels.*;
import java.nio.file.*;

p {
  File path = programFile("lockfile");
  FileChannel channel = FileChannel.open(toPath(path), StandardOpenOption.CREATE, StandardOpenOption.WRITE);
  repeat with sleep 1 {
    {
      temp FileLock lock = channel.tryLock();
      if (lock == null) print("Couldn't lock.");
      else { print("Locked!"); sleepSeconds(1); }
    }
  }
}