现在开始介绍KafkaSpout源码了。
开始时，在open方法中做一些初始化，
........................
_state = new ZkState(stateConf);
_connections = new DynamicPartitionConnections(_spoutConfig, KafkaUtils.makeBrokerReader(conf, _spoutConfig));
// using TransactionalState like this is a hack
int totalTasks = context.getComponentTasks(context.getThisComponentId()).size();
if (_spoutConfig.hosts instanceof StaticHosts) {
_coordinator = new StaticCoordinator(_connections, conf, _spoutConfig, _state, context.getThisTaskIndex(), totalTasks, _uuid);
} else {
_coordinator = new ZkCoordinator(_connections, conf, _spoutConfig, _state, context.getThisTaskIndex(), totalTasks, _uuid);
}
............
前后省略了一些代码，关于metric这系列暂时不介绍。主要是初始化Zookeeper连接zkstate，把kafka Partition 与broker关系对应起来（初始化DynamicPartitionConnections），在 DynamicPartitionConnections构造函数需要传入一个brokerReader，我们是zkHosts，看KafkaUtils代码就知道采用的是ZkBrokerReader，来看下ZkBrokerReader的构造函数代码
public ZkBrokerReader(Map conf, String topic, ZkHosts hosts) {
try {
reader = new DynamicBrokersReader(conf, hosts.brokerZkStr, hosts.brokerZkPath, topic);
cachedBrokers = reader.getBrokerInfo();
lastRefreshTimeMs = System.currentTimeMillis();
refreshMillis = hosts.refreshFreqSecs * 1000L;
} catch (java.net.SocketTimeoutException e) {
LOG.warn("Failed to update brokers", e);
}
}
有一个refreshMillis参数，这个参数是定时更新zk中partition的信息，
//ZkBrokerReader
@Override
public GlobalPartitionInformation getCurrentBrokers() {
long currTime = System.currentTimeMillis();
if (currTime > lastRefreshTimeMs + refreshMillis) { // 当前时间大于和上次更新时间之差大于refreshMillis
try {
LOG.info("brokers need refreshing because " + refreshMillis + "ms have expired");
cachedBrokers = reader.getBrokerInfo();
lastRefreshTimeMs = currTime;
} catch (java.net.SocketTimeoutException e) {
LOG.warn("Failed to update brokers", e);
}
}
return cachedBrokers;
}
// 下面是调用DynamicBrokersReader 的代码
/**
* Get all partitions with their current leaders
*/
public GlobalPartitionInformation getBrokerInfo() throws SocketTimeoutException {
GlobalPartitionInformation globalPartitionInformation = new GlobalPartitionInformation();
try {
int numPartitionsForTopic = getNumPartitions();
String brokerInfoPath = brokerPath();
for (int partition = 0; partition < numPartitionsForTopic; partition++) {
int leader = getLeaderFor(partition);
String path = brokerInfoPath + "/" + leader;
try {
byte[] brokerData = _curator.getData().forPath(path);
Broker hp = getBrokerHost(brokerData);
globalPartitionInformation.addPartition(partition, hp);
} catch (org.apache.zookeeper.KeeperException.NoNodeException e) {
LOG.error("Node {} does not exist ", path);
}
}
} catch (SocketTimeoutException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException(e);
}
LOG.info("Read partition info from zookeeper: " + globalPartitionInformation);
return globalPartitionInformation;
}
GlobalPartitionInformation是一个Iterator类，存放了paritition与broker之间的对应关系， DynamicPartitionConnections中维护Kafka Consumer与parittion之间的关系，每个Consumer读取哪些paritition信息。这个COnnectionInfo信息会在storm.kafka.ZkCoordinator中会被初始化和更新，需要提到的一点是一个KafkaSpout包含一个SimpleConsumer
//storm.kafka.DynamicPartitionConnections
static class ConnectionInfo {
SimpleConsumer consumer;
Set<Integer> partitions = new HashSet();
public ConnectionInfo(SimpleConsumer consumer) {
this.consumer = consumer;
}
}
再看ZkCoordinator类，看其构造函数
//storm.kafka.ZkCoordinator_refreshFreqMs就是定时更新zk partition到本地的操作，在kafkaSpout中nextTuple方法中每次都会去调用 ZkCoordinator的getMyManagedPartitions方法。该方法根据_refreshFreqMs参数定时更新partition信息
public ZkCoordinator(DynamicPartitionConnections connections, Map stormConf, SpoutConfig spoutConfig, ZkState state, int taskIndex, int totalTasks, String topologyInstanceId, DynamicBrokersReader reader) {
_spoutConfig = spoutConfig;
_connections = connections;
_taskIndex = taskIndex;
_totalTasks = totalTasks;
_topologyInstanceId = topologyInstanceId;
_stormConf = stormConf;
_state = state;
ZkHosts brokerConf = (ZkHosts) spoutConfig.hosts;
_refreshFreqMs = brokerConf.refreshFreqSecs * 1000;
_reader = reader;
}
//storm.kafka.ZkCoordinator
@Override
public List<PartitionManager> getMyManagedPartitions() {
if (_lastRefreshTime == null || (System.currentTimeMillis() - _lastRefreshTime) > _refreshFreqMs) {
refresh();
_lastRefreshTime = System.currentTimeMillis();
}
return _cachedList;
}
@Override
public void refresh() {
try {
LOG.info(taskId(_taskIndex, _totalTasks) + "Refreshing partition manager connections");
GlobalPartitionInformation brokerInfo = _reader.getBrokerInfo();
List<Partition> mine = KafkaUtils.calculatePartitionsForTask(brokerInfo, _totalTasks, _taskIndex);
Set<Partition> curr = _managers.keySet();
Set<Partition> newPartitions = new HashSet<Partition>(mine);
newPartitions.removeAll(curr);
Set<Partition> deletedPartitions = new HashSet<Partition>(curr);
deletedPartitions.removeAll(mine);
LOG.info(taskId(_taskIndex, _totalTasks) + "Deleted partition managers: " + deletedPartitions.toString());
for (Partition id : deletedPartitions) {
PartitionManager man = _managers.remove(id);
man.close();
}
LOG.info(taskId(_taskIndex, _totalTasks) + "New partition managers: " + newPartitions.toString());
for (Partition id : newPartitions) {
PartitionManager man = new PartitionManager(_connections, _topologyInstanceId, _state, _stormConf, _spoutConfig, id);
_managers.put(id, man);
}
} catch (Exception e) {
throw new RuntimeException(e);
}
_cachedList = new ArrayList<PartitionManager>(_managers.values());
LOG.info(taskId(_taskIndex, _totalTasks) + "Finished refreshing");
}
其中每个Consumer分配partition的算法是KafkaUtils.calculatePartitionsForTask(brokerInfo, _totalTasks, _taskIndex);
主要做的工作就是获取并行的task数，与当前partition做比较，得出一个COnsumer要负责哪些parititons的读取，具体算法去kafka文档吧
以上在KafkaSpout中做完了初始化操作，下面开始取数据发射数据了，来看nextTuple方法
// storm.kafka.KafkaSpout看完上述代码可知，所有的操作都是在PartitionManager中进行的， PartitionManager中会读取message信息，然后进行发射，主要逻辑在PartitionManager的next方法中
@Override
public void nextTuple() {
List<PartitionManager> managers = _coordinator.getMyManagedPartitions();
for (int i = 0; i < managers.size(); i++) {
try {
// in case the number of managers decreased
_currPartitionIndex = _currPartitionIndex % managers.size();
EmitState state = managers.get(_currPartitionIndex).next(_collector);
if (state != EmitState.EMITTED_MORE_LEFT) {
_currPartitionIndex = (_currPartitionIndex + 1) % managers.size();
}
if (state != EmitState.NO_EMITTED) {
break;
}
} catch (FailedFetchException e) {
LOG.warn("Fetch failed", e);
_coordinator.refresh();
}
}
long now = System.currentTimeMillis();
if ((now - _lastUpdateMs) > _spoutConfig.stateUpdateIntervalMs) {
commit();
}
}
//returns false if it's reached the end of current batch如果_waitingToEmit列表为空，则去读取msg，然后进行逐条发射，每发射一条，break一下，返回EMIT_MORE_LEFT给KafkaSpout的nextTuple方法中，，然后进行判断是否该paritition读取的一次读取的message buffer size是否已发射完毕，如果发射完毕就进行下一个partition 数据读取和发射，
public EmitState next(SpoutOutputCollector collector) {
if (_waitingToEmit.isEmpty()) {
fill();
}
while (true) {
MessageAndRealOffset toEmit = _waitingToEmit.pollFirst();
if (toEmit == null) {
return EmitState.NO_EMITTED;
}
Iterable<List<Object>> tups = KafkaUtils.generateTuples(_spoutConfig, toEmit.msg);
if (tups != null) {
for (List<Object> tup : tups) {
collector.emit(tup, new KafkaMessageId(_partition, toEmit.offset));
}
break;
} else {
ack(toEmit.offset);
}
}
if (!_waitingToEmit.isEmpty()) {
return EmitState.EMITTED_MORE_LEFT;
} else {
return EmitState.EMITTED_END;
}
}
注意的一点是，并不是一次把该partition的所有待发射的msg都发射完再commit offset到zk，而是发射一条，判断一下是否到了该commit的时候了（开始时设置的定时commit时间间隔），笔者认为这样做的原因是为了好控制fail
KafkaSpout中的ack，fail，commit操作全部交给了PartitionManager来做，看代码
@Override
public void ack(Object msgId) {
KafkaMessageId id = (KafkaMessageId) msgId;
PartitionManager m = _coordinator.getManager(id.partition);
if (m != null) {
m.ack(id.offset);
}
}
@Override
public void fail(Object msgId) {
KafkaMessageId id = (KafkaMessageId) msgId;
PartitionManager m = _coordinator.getManager(id.partition);
if (m != null) {
m.fail(id.offset);
}
}
@Override
public void deactivate() {
commit();
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(_spoutConfig.scheme.getOutputFields());
}
private void commit() {
_lastUpdateMs = System.currentTimeMillis();
for (PartitionManager manager : _coordinator.getMyManagedPartitions()) {
manager.commit();
}
}
所以PartitionManager是KafkaSpout的核心，很晚了，都3点多了，后续会不上PartitionManager的分析，晚安