title: In librdkafka, dr_cb() is called each time after produce() called
body: <p>I am working on C++ Kafka client: librdkafka. The lib is here <a href="https://github.com/edenhill/librdkafka/blob/master/examples/rdkafka_example.cpp" rel="nofollow">https://github.com/edenhill/librdkafka/blob/master/examples/rdkafka_example.cpp</a>.
  Each time <strong>produce() in Producer class</strong> is called, is the <strong>dr_cb()</strong> function (see the following code) called?</p>
  
  <pre><code>/**
  * Delivery Report callback class
  */
  class DeliveryReportCb {
  public:
  virtual void dr_cb (Message &amp;message) = 0;
  };
  </code></pre>