c++ - In librdkafka, dr_cb() is called each time after produce() called -

i working on c++ kafka client: librdkafka. lib here https://github.com/edenhill/librdkafka/blob/master/examples/rdkafka_example.cpp. each time produce() in producer class called, dr_cb() function (see following code) called?

/** * delivery report callback class */ class deliveryreportcb { public: virtual void dr_cb (message &message) = 0; }; 

the delivery report callbacks (dr_cb) called when application calls poll() on producer handle, not called within produce() call.