code: public long writeLocked (@Nonnull final LongSupplier aSupplier)
    {
      writeLock ().lock ();
      try
      {
        return aSupplier.getAsLong ();
      }
      finally
      {
        writeLock ().unlock ();
      }
    }
docs: Execute the provided callable in a write lock.
  
  @param aSupplier
  Callable to be executed. May not be <code>null</code>.
  @return The return value of the callable. May be <code>null</code>.