Kafka源代码阅读（7）：producer

概述

send的时候，KafkaProducer把消息放到本地的消息队列RecordAccumulator，然后一个后台线程Sender不断循环，把消息发给Kafka集群。

实际发送方法

    private Future<RecordMetadata> doSend(ProducerRecord<K, V> record, Callback callback) {
        TopicPartition tp = null;

        try {
            
            KafkaProducer.ClusterAndWaitTime clusterAndWaitTime = this.waitOnMetadata(record.topic(), record.partition(), this.maxBlockTimeMs);
            long remainingWaitMs = Math.max(0L, this.maxBlockTimeMs - clusterAndWaitTime.waitedOnMetadataMs);
            Cluster cluster = clusterAndWaitTime.cluster;

            byte[] serializedKey;
            try {
                serializedKey = this.keySerializer.serialize(record.topic(), record.headers(), record.key());
            } catch (ClassCastException var18) {
                throw new SerializationException("Can't convert key of class " + record.key().getClass().getName() + " to class " + this.producerConfig.getClass("key.serializer").getName() + " specified in key.serializer", var18);
            }

            byte[] serializedValue;
            try {
                serializedValue = this.valueSerializer.serialize(record.topic(), record.headers(), record.value());
            } catch (ClassCastException var17) {
                throw new SerializationException("Can't convert value of class " + record.value().getClass().getName() + " to class " + this.producerConfig.getClass("value.serializer").getName() + " specified in value.serializer", var17);
            }

            int partition = this.partition(record, serializedKey, serializedValue, cluster);
            tp = new TopicPartition(record.topic(), partition);
            this.setReadOnly(record.headers());
            Header[] headers = record.headers().toArray();
            int serializedSize = AbstractRecords.estimateSizeInBytesUpperBound(this.apiVersions.maxUsableProduceMagic(), this.compressionType, serializedKey, serializedValue, headers);
            this.ensureValidRecordSize(serializedSize);
            long timestamp = record.timestamp() == null ? this.time.milliseconds() : record.timestamp().longValue();
            this.log.trace("Sending record {} with callback {} to topic {} partition {}", new Object[]{record, callback, record.topic(), partition});
            Callback interceptCallback = this.interceptors == null ? callback : new KafkaProducer.InterceptorCallback(callback, this.interceptors, tp);
            if (this.transactionManager != null && this.transactionManager.isTransactional()) {
                this.transactionManager.maybeAddPartitionToTransaction(tp);
            }

            RecordAppendResult result = this.accumulator.append(tp, timestamp, serializedKey, serializedValue, headers, (Callback)interceptCallback, remainingWaitMs);
            if (result.batchIsFull || result.newBatchCreated) {
                this.log.trace("Waking up the sender since topic {} partition {} is either full or getting a new batch", record.topic(), partition);
                this.sender.wakeup();
            }

            return result.future;
        } catch (Exception) {
            ...
        } 
     
    }