kafka实践（十二）：生产者（KafkaProducer）源码详解和调试

本节对producer的源码解析以熟悉生产者数据发送过程，关于使用Idea对kafka源码编译和调试，参考https://blog.csdn.net/yezonggang/article/details/98212267，本次分析版本是kafka-1.0.0；

一、环境准备

在前面已经完成win环境下zk（3.4.12版本）的运行，并对kafka源码编译， 参考：本地kafka源码的编译和调试，在idea的run-->debug-->中新增configuration来创建topic：yzg（3分区1备份），本地启动运行效果：

二、生产过程和KafkaProducer类解析

KafkaProducer在 org.apache.kafka.clients.producer的包下（所有关于生产者源码都在这包），在使用生产者类时要实例化KafkaProducer，其中定义了发送机制，KafkaProducer是Producer的子类，生产者实例（producer）通过实例化KafkaProducer类，并调用它的send()方法完成数据发送，梳理如下：

1. 首先过一个拦截器；
2. 调用KafkaProducer.send().doSend()方法，doSend首先把key和value按照指定的序列化器进行序列化；
3. partition()函数得到数据和序列化后的数据后，对数据进行分区；
4. 调用RecordAccumulator.append()方法，将处理后的数据扔进RecordAccumulator（缓存对象)的RecordAppendResult类属性中；
5. RecordAccumulator.append()方法首先将数据进行队列化放在Deque对象中，Deque包含多个ProducerBatch；
6. 上面流程完成后，调用this.sender.wakeup()唤醒sender线程，该线程就干一件事就是发数据，

KafkaProducer类的构造函数如下，在生产者实例传入集群config和序列化器后(暂未传入topic名称)，KafkaProducer实例化后完成所有相关属性的实例化，主要的对象有

private KafkaProducer(ProducerConfig config, Serializer<K> keySerializer, Serializer<V> valueSerializer) {
    try {
        Map<String, Object> userProvidedConfigs = config.originals();
        this.producerConfig = config;
        this.time = Time.SYSTEM;
        String clientId = config.getString(ProducerConfig.CLIENT_ID_CONFIG);
        if (clientId.length() <= 0)
            clientId = "producer-" + PRODUCER_CLIENT_ID_SEQUENCE.getAndIncrement();
        this.clientId = clientId;
 
        String transactionalId = userProvidedConfigs.containsKey(ProducerConfig.TRANSACTIONAL_ID_CONFIG) ?
                (String) userProvidedConfigs.get(ProducerConfig.TRANSACTIONAL_ID_CONFIG) : null;
        LogContext logContext;
        if (transactionalId == null)
            logContext = new LogContext(String.format("[Producer clientId=%s] ", clientId));
        else
            logContext = new LogContext(String.format("[Producer clientId=%s, transactionalId=%s] ", clientId, transactionalId));
        log = logContext.logger(KafkaProducer.class);
        log.trace("Starting the Kafka producer");
 
        Map<String, String> metricTags = Collections.singletonMap("client-id", clientId);
        MetricConfig metricConfig = new MetricConfig().samples(config.getInt(ProducerConfig.METRICS_NUM_SAMPLES_CONFIG))
                .timeWindow(config.getLong(ProducerConfig.METRICS_SAMPLE_WINDOW_MS_CONFIG), TimeUnit.MILLISECONDS)
                .recordLevel(Sensor.RecordingLevel.forName(config.getString(ProducerConfig.METRICS_RECORDING_LEVEL_CONFIG)))
                .tags(metricTags);
        List<MetricsReporter> reporters = config.getConfiguredInstances(ProducerConfig.METRIC_REPORTER_CLASSES_CONFIG,
                MetricsReporter.class);
        reporters.add(new JmxReporter(JMX_PREFIX));
        this.metrics = new Metrics(metricConfig, reporters, time);
        ProducerMetrics metricsRegistry = new ProducerMetrics(this.metrics);
        this.partitioner = config.getConfiguredInstance(ProducerConfig.PARTITIONER_CLASS_CONFIG, Partitioner.class);
        long retryBackoffMs = config.getLong(ProducerConfig.RETRY_BACKOFF_MS_CONFIG);
        if (keySerializer == null) {
            this.keySerializer = ensureExtended(config.getConfiguredInstance(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,
                                                                                     Serializer.class));
            this.keySerializer.configure(config.originals(), true);
        } else {
            config.ignore(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG);
            this.keySerializer = ensureExtended(keySerializer);
        }
        if (valueSerializer == null) {
            this.valueSerializer = ensureExtended(config.getConfiguredInstance(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,
                                                                                       Serializer.class));
            this.valueSerializer.configure(config.originals(), false);
        } else {
            config.ignore(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG);
            this.valueSerializer = ensureExtended(valueSerializer);
        }
 
        // load interceptors and make sure they get clientId
        userProvidedConfigs.put(ProducerConfig.CLIENT_ID_CONFIG, clientId);
        List<ProducerInterceptor<K, V>> interceptorList = (List) (new ProducerConfig(userProvidedConfigs, false)).getConfiguredInstances(ProducerConfig.INTERCEPTOR_CLASSES_CONFIG,
                ProducerInterceptor.class);
        this.interceptors = interceptorList.isEmpty() ? null : new ProducerInterceptors<>(interceptorList);
        ClusterResourceListeners clusterResourceListeners = configureClusterResourceListeners(keySerializer, valueSerializer, interceptorList, reporters);
        this.metadata = new Metadata(retryBackoffMs, config.getLong(ProducerConfig.METADATA_MAX_AGE_CONFIG),
                true, true, clusterResourceListeners);
        this.maxRequestSize = config.getInt(ProducerConfig.MAX_REQUEST_SIZE_CONFIG);
        this.totalMemorySize = config.getLong(ProducerConfig.BUFFER_MEMORY_CONFIG);
        this.compressionType = CompressionType.forName(config.getString(ProducerConfig.COMPRESSION_TYPE_CONFIG));
 
        this.maxBlockTimeMs = config.getLong(ProducerConfig.MAX_BLOCK_MS_CONFIG);
        this.requestTimeoutMs = config.getInt(ProducerConfig.REQUEST_TIMEOUT_MS_CONFIG);
        this.transactionManager = configureTransactionState(config, logContext, log);
        int retries = configureRetries(config, transactionManager != null, log);
        int maxInflightRequests = configureInflightRequests(config, transactionManager != null);
        short acks = configureAcks(config, transactionManager != null, log);
 
        this.apiVersions = new ApiVersions();
        this.accumulator = new RecordAccumulator(logContext,
                config.getInt(ProducerConfig.BATCH_SIZE_CONFIG),
                this.totalMemorySize,
                this.compressionType,
                config.getLong(ProducerConfig.LINGER_MS_CONFIG),
                retryBackoffMs,
                metrics,
                time,
                apiVersions,
                transactionManager);
        List<InetSocketAddress> addresses = ClientUtils.parseAndValidateAddresses(config.getList(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG));
        this.metadata.update(Cluster.bootstrap(addresses), Collections.<String>emptySet(), time.milliseconds());
        ChannelBuilder channelBuilder = ClientUtils.createChannelBuilder(config);
        Sensor throttleTimeSensor = Sender.throttleTimeSensor(metricsRegistry.senderMetrics);
        NetworkClient client = new NetworkClient(
                new Selector(config.getLong(ProducerConfig.CONNECTIONS_MAX_IDLE_MS_CONFIG),
                        this.metrics, time, "producer", channelBuilder, logContext),
                this.metadata,
                clientId,
                maxInflightRequests,
                config.getLong(ProducerConfig.RECONNECT_BACKOFF_MS_CONFIG),
                config.getLong(ProducerConfig.RECONNECT_BACKOFF_MAX_MS_CONFIG),
                config.getInt(ProducerConfig.SEND_BUFFER_CONFIG),
                config.getInt(ProducerConfig.RECEIVE_BUFFER_CONFIG),
                this.requestTimeoutMs,
                time,
                true,
                apiVersions,
                throttleTimeSensor,
                logContext);
        this.sender = new Sender(logContext,
                client,
                this.metadata,
                this.accumulator,
                maxInflightRequests == 1,
                config.getInt(ProducerConfig.MAX_REQUEST_SIZE_CONFIG),
                acks,
                retries,
                metricsRegistry.senderMetrics,
                Time.SYSTEM,
                this.requestTimeoutMs,
                config.getLong(ProducerConfig.RETRY_BACKOFF_MS_CONFIG),
                this.transactionManager,
                apiVersions);
        String ioThreadName = NETWORK_THREAD_PREFIX + " | " + clientId;
        this.ioThread = new KafkaThread(ioThreadName, this.sender, true);
        this.ioThread.start();
        this.errors = this.metrics.sensor("errors");
        config.logUnused();
        AppInfoParser.registerAppInfo(JMX_PREFIX, clientId, metrics);
        log.debug("Kafka producer started");
    } catch (Throwable t) {
        // call close methods if internal objects are already constructed this is to prevent resource leak. see KAFKA-2121
        close(0, TimeUnit.MILLISECONDS, true);
        // now propagate the exception
        throw new KafkaException("Failed to construct kafka producer", t);
    }
}

1、数据预处理（拦截器、序列化、分区器、缓存）

① 生产者producer在拿到props后实例化KafkaProducer，然后多线程调用send()，KafkaProducer如果没有定义拦截器interceptors（ProducerInterceptors类的实例）数据record保持不变，若定义了interceptors就调用拦截器的ProducerInterceptors.onSend()方法过滤数据record，这个拦截器就是用来自定义的，源码里面没有过滤方法；

public Future<RecordMetadata> send(ProducerRecord<K, V> record, Callback callback) {
    // intercept the record, which can be potentially modified; this method does not throw exceptions
    ProducerRecord<K, V> interceptedRecord = this.interceptors == null ? record : this.interceptors.onSend(record);
    return doSend(interceptedRecord, callback);
}

② 接下来调用doSend方法，方法体内首先调用partition()方法，入参是原始的record数据，以及key和value序列化结果；

// 确认topic和集群信息正确
ClusterAndWaitTime clusterAndWaitTime = waitOnMetadata(record.topic(), record.partition(), maxBlockTimeMs);
Cluster cluster = clusterAndWaitTime.cluster;
// 分区器
int partition = partition(record, serializedKey, serializedValue, cluster);
tp = new TopicPartition(record.topic(), partition);
//如果没有指定分区，就使用内置的分区器partitioner.partition()
private int partition(ProducerRecord<K, V> record, byte[] serializedKey, byte[] serializedValue, Cluster cluster) {
    Integer partition = record.partition();
    return partition != null ?
            partition :
            partitioner.partition(
                    record.topic(), record.key(), serializedKey, record.value(), serializedValue, cluster);

③ 接下来调用KafkaProducer类持有的RecordAccumulator对象的RecordAccumulator.append()方法，返回RecordAppendResult对象；

RecordAccumulator.RecordAppendResult result = accumulator.append(tp, timestamp, serializedKey,
        serializedValue, headers, interceptCallback, remainingWaitMs);
// append方法的实现，返回RecordAppendResult 对象
public RecordAppendResult append(TopicPartition tp,
                                 long timestamp,
                                 byte[] key,
                                 byte[] value,
                                 Header[] headers,
                                 Callback callback,
                                 long maxTimeToBlock) throws InterruptedException {
    appendsInProgress.incrementAndGet();
    ByteBuffer buffer = null;
    if (headers == null) headers = Record.EMPTY_HEADERS;
    try {
        Deque<ProducerBatch> dq = getOrCreateDeque(tp);
        synchronized (dq) {
            if (closed)
                throw new IllegalStateException("Cannot send after the producer is closed.");
            RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq);
            if (appendResult != null)
                return appendResult;
        }
        byte maxUsableMagic = apiVersions.maxUsableProduceMagic();
        int size = Math.max(this.batchSize, AbstractRecords.estimateSizeInBytesUpperBound(maxUsableMagic, compression, key, value, headers));
        log.trace("Allocating a new {} byte message buffer for topic {} partition {}", size, tp.topic(), tp.partition());
        buffer = free.allocate(size, maxTimeToBlock);
        synchronized (dq) {
            if (closed)
                throw new IllegalStateException("Cannot send after the producer is closed.");
 
            RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq);
            if (appendResult != null) {
                return appendResult;
            }
            MemoryRecordsBuilder recordsBuilder = recordsBuilder(buffer, maxUsableMagic);
            ProducerBatch batch = new ProducerBatch(tp, recordsBuilder, time.milliseconds());
            FutureRecordMetadata future = Utils.notNull(batch.tryAppend(timestamp, key, value, headers, callback, time.milliseconds()));
            dq.addLast(batch);
            incomplete.add(batch);
            buffer = null;
            return new RecordAppendResult(future, dq.size() > 1 || batch.isFull(), true);
        }
    } finally {
        if (buffer != null)
            free.deallocate(buffer);
        appendsInProgress.decrementAndGet();
    }
}

④ 继续上面的代码，生产者本地维护一个未发送数据的缓存池，也是一个后台IO线程用来将records转换为网络请求，这就是RecordAccumulator，RecordAccumulator持有RecordAppendResult对象，其future作为整个producer.send()方法的返回值；

public final static class RecordAppendResult {
    public final FutureRecordMetadata future;
    public final boolean batchIsFull;
    public final boolean newBatchCreated;
 
    public RecordAppendResult(FutureRecordMetadata future, boolean batchIsFull, boolean newBatchCreated) {
        this.future = future;
        this.batchIsFull = batchIsFull;
        this.newBatchCreated = newBatchCreated;
    }
}

RecordAccumulator通过getOrCreateDeque(tp)得到deque队列（持有ProducerBatch对象），ProducerBatch是最小的发送数据实体，RecordAccumulator计算字节数并分配本地资源，不断往deque队列新增ProducerBatch对象；

Deque<ProducerBatch> dq = getOrCreateDeque(tp);

至此 KafkaProducer.send()方法的逻辑结束，也就是原始数据经过逻辑转换后放在本地的Deque队列中；2、sender线程处理

在KafkaProducer实例化后sender也被实例化，KafkaProducer.send().doSend()会通过this.sender.wakeup()把线程方法启动，它持有一个NetworkClient实例，sender实例的run()方法包含对NetworkClient的处理逻辑。

// 网络请求的构造器
NetworkClient client = new NetworkClient(
        new Selector(config.getLong(ProducerConfig.CONNECTIONS_MAX_IDLE_MS_CONFIG),
                this.metrics, time, "producer", channelBuilder, logContext),
        this.metadata,
        clientId,
        maxInflightRequests,
        config.getLong(ProducerConfig.RECONNECT_BACKOFF_MS_CONFIG),
        config.getLong(ProducerConfig.RECONNECT_BACKOFF_MAX_MS_CONFIG),
        config.getInt(ProducerConfig.SEND_BUFFER_CONFIG),
        config.getInt(ProducerConfig.RECEIVE_BUFFER_CONFIG),
        this.requestTimeoutMs,
        time,
        true,
        apiVersions,
        throttleTimeSensor,
        logContext);
 
// run方法中对于网络请求的逻辑
void run(long now) {
    if (transactionManager != null) {
        try {
            if (transactionManager.shouldResetProducerStateAfterResolvingSequences())
                // Check if the previous run expired batches which requires a reset of the producer state.
                transactionManager.resetProducerId();
 
            if (!transactionManager.isTransactional()) {
                // this is an idempotent producer, so make sure we have a producer id
                maybeWaitForProducerId();
            } else if (transactionManager.hasUnresolvedSequences() && !transactionManager.hasFatalError()) {
                transactionManager.transitionToFatalError(new KafkaException("The client hasn't received acknowledgment for " +
                        "some previously sent messages and can no longer retry them. It isn't safe to continue."));
            } else if (transactionManager.hasInFlightTransactionalRequest() || maybeSendTransactionalRequest(now)) {
                // as long as there are outstanding transactional requests, we simply wait for them to return
                client.poll(retryBackoffMs, now);
                return;
            }
 
            // do not continue sending if the transaction manager is in a failed state or if there
            // is no producer id (for the idempotent case).
            if (transactionManager.hasFatalError() || !transactionManager.hasProducerId()) {
                RuntimeException lastError = transactionManager.lastError();
                if (lastError != null)
                    maybeAbortBatches(lastError);
                client.poll(retryBackoffMs, now);
                return;
            } else if (transactionManager.hasAbortableError()) {
                accumulator.abortUndrainedBatches(transactionManager.lastError());
            }
        } catch (AuthenticationException e) {
            // This is already logged as error, but propagated here to perform any clean ups.
            log.trace("Authentication exception while processing transactional

三、生产者demo使用和调试

源码编译运行后相当于本地搭建了kafka集群，在源码examples包下 producer类来了解数据发送流程，首先定义kafka提供的KafkaProducer类，再调用它的send(）方法发送数据；很多工作是在KafkaProducer类实例化的时候已经做了；

    producer类需定义key和value、topic名称、同步或者异步，然后构造器指定kafka集群地址，生产者id（可选），序列化器
    producer线程类的执行方法（while死循环），判断是异步还是同步发送配置（高版本默认都异步），调用send方法发送数据,send方法的第1个参数是ProducerRecord，第2个是messageNo记录发送批次，第3个是数据record，DemoCallBack是回执类（不是函数）
    callback类有开始时间、自增的messageno、messageStr字符串三个参数，并重写onCompletion方法来定义异常；

稍微修改这个实现类进行调试，集群是idea在运行的本地集群（127.0.0.1:9092），指定的topic是yezonggang，异步发送，producer.send()方法写在线程方法内调用，如下：

package demo;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerRecord;
import java.util.Properties;
import java.util.concurrent.ExecutionException;
 
public class DemoForProducer extends Thread{
 
    public static void main(String[] args) {
        //System.out.println("hello");
        DemoForProducer dfp=new DemoForProducer("yezonggang",true);
                dfp.run();
    }
    private final KafkaProducer<Integer, String> producer;
    private final String topic;
    private  final Boolean isAsync;
 
    public DemoForProducer(String topic, Boolean isAsync) {
        Properties props = new Properties();
        props.put("bootstrap.servers", "127.0.0.1:9092");
        props.put("client.id", "DemoForProducer");
        props.put("key.serializer", "org.apache.kafka.common.serialization.IntegerSerializer");
        props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
        producer = new KafkaProducer<>(props);
        this.topic = topic;
        this.isAsync = isAsync;
    }
    public DemoForProducer(KafkaProducer<Integer, String> producer, String topic, Boolean isAsync) {
        this.producer = producer;
        this.topic = topic;
        this.isAsync = isAsync;
    }
 
    // 线程类的执行方法（while死循环），判断是异步还是同步发送配置（高版本默认都异步），调用send方法发送数据,send方法的第1个参数是ProducerRecord，第2个是messageNo记录发送批次，DemoCallBack是回执函数
    public void run() {
        int messageNo = 1;
        while (true) {
            String messageStr = "Message_" + messageNo;
            long startTime = System.currentTimeMillis();
            if (isAsync) { // Send asynchronously
                producer.send(new ProducerRecord<>(topic,
                        messageNo,
                        messageStr), new DemoForCallBack(startTime, messageNo, messageStr));
            } else { // Send synchronously
                try {
                    producer.send(new ProducerRecord<>(topic,
                            messageNo,
                            messageStr)).get();
                    System.out.println("Sent message: (" + messageNo + ", " + messageStr + ")");
                } catch (InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }
            }
            ++messageNo;
        }
    }
}

在 KafkaProducer类实例化后，idea中运行的本地kafka集群就已经拿到了producerconfig设置，如下，client.id=DemoForProducer已经说明该生产者已经被kafka集群捕获，即使当前send()方法还未启动；

ProducerRecord(topic=yezonggang, partition=null, headers=RecordHeaders(headers = [], isReadOnly = false), key=1, value=Message_1, timestamp=null)

INFO ProducerConfig values: 
acks = 1
batch.size = 16384
bootstrap.servers = [127.0.0.1:9092]
buffer.memory = 33554432
client.id = DemoForProducer
compression.type = none
connections.max.idle.ms = 540000
enable.idempotence = false
interceptor.classes = null
key.serializer = class org.apache.kafka.common.serialization.IntegerSerializer
linger.ms = 0
max.block.ms = 60000
max.in.flight.requests.per.connection = 5
max.request.size = 1048576
metadata.max.age.ms = 300000
metric.reporters = []
metrics.num.samples = 2
metrics.recording.level = INFO
metrics.sample.window.ms = 30000
partitioner.class = class org.apache.kafka.clients.producer.internals.DefaultPartitioner
receive.buffer.bytes = 32768
reconnect.backoff.max.ms = 1000
reconnect.backoff.ms = 50
request.timeout.ms = 30000
retries = 0
retry.backoff.ms = 100
sasl.jaas.config = null
sasl.kerberos.kinit.cmd = /usr/bin/kinit
sasl.kerberos.min.time.before.relogin = 60000
sasl.kerberos.service.name = null
sasl.kerberos.ticket.renew.jitter = 0.05
sasl.kerberos.ticket.renew.window.factor = 0.8
sasl.mechanism = GSSAPI
security.protocol = PLAINTEXT
send.buffer.bytes = 131072
ssl.cipher.suites = null
ssl.enabled.protocols = [TLSv1.2, TLSv1.1, TLSv1]
ssl.endpoint.identification.algorithm = null
ssl.key.password = null
ssl.keymanager.algorithm = SunX509
ssl.keystore.location = null
ssl.keystore.password = null
ssl.keystore.type = JKS
ssl.protocol = TLS
ssl.provider = null
ssl.secure.random.implementation = null
ssl.trustmanager.algorithm = PKIX
ssl.truststore.location = null
ssl.truststore.password = null
ssl.truststore.type = JKS
transaction.timeout.ms = 60000
transactional.id = null
value.serializer = class org.apache.kafka.common.serialization.StringSerializer(org.apache.kafka.clients.producer.ProducerConfig)

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