librdkafkaexamplemodeC

/*结构体说明  
 rd_kafka_toppar_s：topic & partition combination
 rd_kafka_topic:
 rd_kafka_q_s rd_kafka_q_t：队列操作
   
*/
 else if (mode == 'C') {
                /*
                 * Consumer
                 */
                //初始化设置
                rd_kafka_conf_set(conf, "enable.partition.eof", "true", NULL,
                                  0);

                /* Create Kafka handle */
                //判断是否可以使用当前consumer

                if (!(rk = rd_kafka_new(RD_KAFKA_CONSUMER, conf, errstr,
                                        sizeof(errstr)))) {
                        fprintf(stderr,
                                "%% Failed to create new consumer: %s\n",
                                errstr);
                        exit(1);
                }
                //当设置-s:watermark使用
                if (get_wmarks) {
                        int64_t lo, hi;

                        /* Only query for hi&lo partition watermarks */

                        if ((err = rd_kafka_query_watermark_offsets(
                                 rk, topic, partition, &lo, &hi, 5000))) {
                                fprintf(stderr,
                                        "%% query_watermark_offsets() "
                                        "failed: %s\n",
                                        rd_kafka_err2str(err));
                                exit(1);
                        }

                        printf(
                            "%s [%d]: low - high offsets: "
                            "%" PRId64 " - %" PRId64 "\n",
                            topic, partition, lo, hi);

                        rd_kafka_destroy(rk);
                        exit(0);
                }


                /* Create topic */
                rkt        = rd_kafka_topic_new(rk, topic, topic_conf);
                topic_conf = NULL; /* Now owned by topic */

                /* Start consuming */
                //判断是否可以消费
                /*rd_kafka_consume_start 
                  判断条件：
                  1.topic是否长度超限 是否为空
                  2.加线程锁
                  3.判断offset(最新，最小，上次消费的地方) 判断offset是否合法 */

                if (rd_kafka_consume_start(rkt, partition, start_offset) ==
                    -1) {
                        err = rd_kafka_last_error();
                        fprintf(stderr, "%% Failed to start consuming: %s\n",
                                rd_kafka_err2str(err));
                        if (err == RD_KAFKA_RESP_ERR__INVALID_ARG)
                                fprintf(stderr,
                                        "%% Broker based offset storage "
                                        "requires a group.id, "
                                        "add: -X group.id=yourGroup\n");
                        exit(1);
                }
                /*
                 
                */
                while (run) {
                        rd_kafka_message_t *rkmessage;

                        /* Poll for errors, etc. */
                        rd_kafka_poll(rk, 0);

                        /* Consume single message.
                         * See rdkafka_performance.c for high speed
                         * consuming of messages. */
                        rkmessage = rd_kafka_consume(rkt, partition, 1000);
                        if (!rkmessage) /* timeout */
                                continue;

                        msg_consume(rkmessage, NULL);

                        /* Return message to rdkafka */
                        rd_kafka_message_destroy(rkmessage);

                        if (seek_offset) {
                                err = rd_kafka_seek(rkt, partition, seek_offset,
                                                    2000);
                                if (err)
                                        printf("Seek failed: %s\n",
                                               rd_kafka_err2str(err));
                                else
                                        printf("Seeked to %" PRId64 "\n",
                                               seek_offset);
                                seek_offset = 0;
                        }
                }

                /* Stop consuming */
                rd_kafka_consume_stop(rkt, partition);

                while (rd_kafka_outq_len(rk) > 0)
                        rd_kafka_poll(rk, 10);

                /* Destroy topic */
                rd_kafka_topic_destroy(rkt);

                /* Destroy handle */
                rd_kafka_destroy(rk);

        }

rd_kafka_message_t *
rd_kafka_consume(rd_kafka_topic_t *app_rkt, int32_t partition, int timeout_ms) {
        rd_kafka_topic_t *rkt = rd_kafka_topic_proper(app_rkt);
        rd_kafka_toppar_t *rktp;
        rd_kafka_message_t *rkmessage;

        rd_kafka_topic_rdlock(rkt);
        rktp = rd_kafka_toppar_get(rkt, partition, 0 /*no ua on miss*/);
        if (unlikely(!rktp))
                rktp = rd_kafka_toppar_desired_get(rkt, partition);
        rd_kafka_topic_rdunlock(rkt);

        if (unlikely(!rktp)) {
                /* No such toppar known */
                rd_kafka_set_last_error(RD_KAFKA_RESP_ERR__UNKNOWN_PARTITION,
                                        ESRCH);
                return NULL;
        }

        rkmessage =
            rd_kafka_consume0(rkt->rkt_rk, rktp->rktp_fetchq, timeout_ms);

        rd_kafka_toppar_destroy(rktp); /* refcnt from .._get() */

        return rkmessage;
}