    # File lib/sqlite3/driver/dl/driver.rb, line 140
        def trace( db, data=nil, &block )
          @trace_handler = block

          unless @trace_handler_callback
            @trace_handler_callback = ::DL.callback( "IPS" ) do |cookie,sql|
              @trace_handler.call( cookie ? cookie.to_object : nil, sql ) || 0
            end
          end

          API.sqlite3_trace( db, block&&@trace_handler_callback, data )
        end