# File lib/amalgalite/database.rb, line 847
    def define_busy_handler( callable = nil, &block )
      handler = ( callable || block ).to_proc
      a = handler.arity
      raise BusyHandlerError, "A busy handler expects 1 and only 1 argument, not #{a}" if a != 1
      @api.busy_handler( handler )
    end