code: func (locker *MemoryLocker) LockUpload(id string) error {
  	locker.mutex.Lock()
  	defer locker.mutex.Unlock()
  
  	// Ensure file is not locked
  	if _, ok := locker.locks[id]; ok {
  		return tusd.ErrFileLocked
  	}
  
  	locker.locks[id] = struct{}{}
  
  	return nil
  }
docs: // LockUpload tries to obtain the exclusive lock.