sclass FileBasedLock implements AutoCloseable {
  File lockFile;
  double timeout = 60.0;
  bool haveLock;
  java.util.Timer touchTimer;
  
  // returns true iff lock was acquired
  synchronized bool tryToLock() {
    if (haveLock) ret;
    
    double age = fileAgeInSeconds(lockFile);
    if (age >= timeout) {
      print("Deleting old lock file: " + lockFile + " (age: " + iround(age) + " seconds)");
      deleteFile(lockFile);
    }
    
    try {
      Files.createFile(lockFile);
      set haveLock;
      startTouchTimer();
      true;
    } catch e {
      printExceptionShort(e);
      false;
    }
  }
  
  synchronized void startTouchTimer {
    if (timer != null) ret;
    timer = doEvery(timeout/2, r doTouch);
  }

  synchronized void doTouch {
    if (haveLock)
      touchFile(lockFile);
  }
     
  public void close {
    dispose touchTimer;
  }
}