在上一篇中介绍了Receiver在Driver的精妙实现，本篇内容主要介绍Receiver在Executor中的启动，数据接收和存储
从ReceiverTracker的start方法开始，调用launchReceivers()方法，给endpoint发送消息，endpoint.send(StartAllReceivers(receivers))，endpoint就是ReceiverTrackerEndpoint，也可以说是给自己的消息通讯体发送了一条消息。看接收到的消息
case StartAllReceivers(receivers) =>
val scheduledLocations = schedulingPolicy.scheduleReceivers(receivers, getExecutors) // 循环启动receiver
for (receiver <- receivers) {
val executors = scheduledLocations(receiver.streamId)
updateReceiverScheduledExecutors(receiver.streamId, executors)
receiverPreferredLocations(receiver.streamId) = receiver.preferredLocation //启动receiver
startReceiver(receiver, executors)
}startReceiver(receiver, executors)循环调用，每一个receiver会启动一个job。startReceiver的代码如下
private def startReceiver(
receiver: Receiver[_],
scheduledLocations: Seq[TaskLocation]): Unit = {
def shouldStartReceiver: Boolean = { // It's okay to start when trackerState is Initialized or Started
!(isTrackerStopping || isTrackerStopped)
}
val receiverId = receiver.streamId if (!shouldStartReceiver) {
onReceiverJobFinish(receiverId) return
}
val checkpointDirOption = Option(ssc.checkpointDir)
val serializableHadoopConf = new SerializableConfiguration(ssc.sparkContext.hadoopConfiguration) // Function to start the receiver on the worker node
// 在worker节点启动receiver的方法，（就是action中的方法）
val startReceiverFunc: Iterator[Receiver[_]] => Unit =
(iterator: Iterator[Receiver[_]]) => { if (!iterator.hasNext) { throw new SparkException("Could not start receiver as object not found.")
} //判断task的重试次数为0，就是没有task失败后，重试运行不执行以下代码
if (TaskContext.get().attemptNumber() == 0) {
val receiver = iterator.next()
assert(iterator.hasNext == false) //这里创建接收器管理者，在start方法里启动receiver接收数据
val supervisor = new ReceiverSupervisorImpl(receiver, SparkEnv.get, serializableHadoopConf.value, checkpointDirOption)
supervisor.start()
supervisor.awaitTermination()
} else { // It's restarted by TaskScheduler, but we want to reschedule it again. So exit it.
}
} // Create the RDD using the scheduledLocations to run the receiver in a Spark job
// 创建接收数据的RDD
val receiverRDD: RDD[Receiver[_]] = if (scheduledLocations.isEmpty) { //
ssc.sc.makeRDD(Seq(receiver), 1)
} else { // 根据数据本地性创建receiverRDD
val preferredLocations = scheduledLocations.map(_.toString).distinct
ssc.sc.makeRDD(Seq(receiver -> preferredLocations))
} // 对job进行一些配置
receiverRDD.setName(s"Receiver $receiverId")
ssc.sparkContext.setJobDescription(s"Streaming job running receiver $receiverId")
ssc.sparkContext.setCallSite(Option(ssc.getStartSite()).getOrElse(Utils.getCallSite())) // 到这里就提交了receiverRDD到集群中
val future = ssc.sparkContext.submitJob[Receiver[_], Unit, Unit](receiverRDD, startReceiverFunc, Seq(0), (_, _) => Unit, ()) // We will keep restarting the receiver job until ReceiverTracker is stopped
future.onComplete { case Success(_) => if (!shouldStartReceiver) {
onReceiverJobFinish(receiverId)
} else { // 重启receiver
logInfo(s"Restarting Receiver $receiverId") self.send(RestartReceiver(receiver))
} case Failure(e) => if (!shouldStartReceiver) {
onReceiverJobFinish(receiverId)
} else {
logError("Receiver has been stopped. Try to restart it.", e)
logInfo(s"Restarting Receiver $receiverId") // 重启receiver
self.send(RestartReceiver(receiver))
}
}(submitJobThreadPool)
logInfo(s"Receiver ${receiver.streamId} started")
}在startReceiverFunc函数中定义了从iterator中取一条记录，也就是receiver,然后实例化一个ReceiverSupervisorImpl,把receiver传递进入，然后调用ReceiverSupervisorImpl的start方法。当然这里并没有启动ReceiverSupervisorImpl，只是定义了操作而已，真正的执行是在Executor中。
然后提交ReceiverRDD到集群运行，代码如下
val future = ssc.sparkContext.submitJob[Receiver[_], Unit, Unit](receiverRDD, startReceiverFunc, Seq(0), (_, _) => Unit, ())
通过startReceiverFunc函数 来看ReceiverSupervisorImpl在Executor上的运行。
从supervisor.start()开始，start方法代码如下
def start() {
onStart()
startReceiver()
}onStart方法代码如下
/**
* Called when supervisor is started.
* Note that this must be called before the receiver.onStart() is called to ensure
* things like [[BlockGenerator]]s are started before the receiver starts sending data.
*/protected def onStart() { }重点是看onStart的注释，注释内容说在receiver.onStart()之前，必须BlockGenerator先启动，以保证接收到的数据能够被存储起来。看onStart方法的子类实现，代码如下
override protected def onStart() {
registeredBlockGenerators.foreach { _.start() }
}registeredBlockGenerators在ReceiverSupervisorImpl实例化的时候创建，代码如下
private val registeredBlockGenerators = new mutable.ArrayBuffer[BlockGenerator]
registeredBlockGenerators在createBlockGenerator方法中添加了BlockGenerator，代码如下
override def createBlockGenerator(blockGeneratorListener: BlockGeneratorListener): BlockGenerator = { // Cleanup BlockGenerators that have already been stopped
registeredBlockGenerators --= registeredBlockGenerators.filter{ _.isStopped() } // 每一个receiver创建一个BlockGenerator，因为streamId一一对应receiver
val newBlockGenerator = new BlockGenerator(blockGeneratorListener, streamId, env.conf)
registeredBlockGenerators += newBlockGenerator
newBlockGenerator
}那么createBlockGenerator在什么时候被调用呢？看代码
private val defaultBlockGenerator = createBlockGenerator(defaultBlockGeneratorListener)
registeredBlockGenerators的BlockGenerator已经有了，看BlockGenerator的start()方法,代码如下
def start(): Unit = synchronized { if (state == Initialized) {
state = Active
blockIntervalTimer.start()
blockPushingThread.start()
logInfo("Started BlockGenerator")
} else { throw new SparkException(
s"Cannot start BlockGenerator as its not in the Initialized state [state = $state]")
}
}这里启动了blockIntervalTimer和blockPushingThread，blockIntervalTimer就是一个定时器，默认每200ms回调一下updateCurrentBuffer方法，回调时间通过参数spark.streaming.blockInterval设置，这也是一个性能调优的参数，时间过短太造成block碎片太多，时间过长可能导致block块过大，具体时间长短要根据实际业务而定，updateCurrentBuffer方法作用就是将接收到的数据包装到block存储，代码后面再看;blockPushingThread作用是定时从blocksForPushing队列中取block，然后存储，并向ReceiverTrackerEndpoint汇报，代码后面再看
BlockGenerator启动之后接着看 supervisor.start()方法中的 startReceiver()方法， startReceiver()代码如下
def startReceiver(): Unit = synchronized { try { if (onReceiverStart()) {
logInfo("Starting receiver")
receiverState = Started
receiver.onStart()
logInfo("Called receiver onStart")
} else { // The driver refused us
stop("Registered unsuccessfully because Driver refused to start receiver " + streamId, None)
}
} catch { case NonFatal(t) =>
stop("Error starting receiver " + streamId, Some(t))
}
}首先判断onReceiverStart()的返回值，onReceiverStart()代码在子类中的实现如下
override protected def onReceiverStart(): Boolean = {
val msg = RegisterReceiver(
streamId, receiver.getClass.getSimpleName, host, executorId, endpoint)
trackerEndpoint.askWithRetry[Boolean](msg)
}onReceiverStart内部向trackerEndpoint发送了一条RegisterReceiver注册receiver的消息，在trackerEndpoint内部收到消息后，将注册信息包装到一个ReceiverTrackingInfo的case class类中，然后把ReceiverTrackingInfo按照k-v的方式put到receiverTrackingInfos中，key就是streamId，再次说明一个inputDstream对应一个receiver。
回到上面的调用返回true,将receiverState 标记为Started，然后调用了receiver的onStart方法。
以SocketReceiver为例，看SocketReceiver的onStart方法 ,启动了一条后台线程，调用receive()方法接收数据，代码如下
def onStart() { // Start the thread that receives data over a connection
new Thread("Socket Receiver") {
setDaemon(true)
override def run() { receive() }
}.start()
}接着看receive()方法，代码如下
def receive() { var socket: Socket = null
try {
logInfo("Connecting to " + host + ":" + port)
socket = new Socket(host, port)
logInfo("Connected to " + host + ":" + port)
val iterator = bytesToObjects(socket.getInputStream()) while(!isStopped && iterator.hasNext) {
store(iterator.next)
} if (!isStopped()) {
restart("Socket data stream had no more data")
} else {
logInfo("Stopped receiving")
}
} catch { case e: java.net.ConnectException =>
restart("Error connecting to " + host + ":" + port, e) case NonFatal(e) =>
logWarning("Error receiving data", e)
restart("Error receiving data", e)
} finally { if (socket != null) {
socket.close()
logInfo("Closed socket to " + host + ":" + port)
}
}
}receiver方法的内容就很简单了，启动一个socket接收数据，接收一行就调用store方法存储起来，store方法的代码如下
def store(dataItem: T) {
supervisor.pushSingle(dataItem)
}调用supervisor的pushSingle方法，supervisor就是ReceiverSupervisor的实现类ReceiverSupervisorImpl的方法，代码如下
def pushSingle(data: Any) {
defaultBlockGenerator.addData(data)
}defaultBlockGenerator在上面说过，他是ReceiverSupervisorImpl的一个成员变量，接着看他的addData方法，代码如下
def addData(data: Any): Unit = { if (state == Active) {
waitToPush() synchronized { if (state == Active) {
currentBuffer += data
} else { throw new SparkException( "Cannot add data as BlockGenerator has not been started or has been stopped")
}
}
} else { throw new SparkException( "Cannot add data as BlockGenerator has not been started or has been stopped")
}
}currentBuffer += data,在currentBuffer 上不断的累加数据，那么currentBuffer 的数据是怎样存储起来的呢，这时候就用到了前面介绍的 blockIntervalTimer和blockPushingThread
首先看blockIntervalTimer定时回调的updateCurrentBuffer()方法，代码如下
private def updateCurrentBuffer(time: Long): Unit = { try { var newBlock: Block = null
synchronized { if (currentBuffer.nonEmpty) {
val newBlockBuffer = currentBuffer
currentBuffer = new ArrayBuffer[Any]
val blockId = StreamBlockId(receiverId, time - blockIntervalMs)
listener.onGenerateBlock(blockId)
newBlock = new Block(blockId, newBlockBuffer)
}
} if (newBlock != null) {
blocksForPushing.put(newBlock) // put is blocking when queue is full
}
} catch { case ie: InterruptedException =>
logInfo("Block updating timer thread was interrupted") case e: Exception =>
reportError("Error in block updating thread", e)
}
}将currentBuffer交给newBlockBuffer ，然后实例化一个空的ArrayBuffer给currentBuffer，接着实例化一个Block把newBlockBuffer 传递进去，最后把newBlock 放入到blocksForPushing队列中
接下来就是blockPushingThread干的活了，在blockPushingThread线程中调用keepPushingBlocks方法，代码如下
private def keepPushingBlocks() {
logInfo("Started block pushing thread")
def areBlocksBeingGenerated: Boolean = synchronized {
state != StoppedGeneratingBlocks
} try { // While blocks are being generated, keep polling for to-be-pushed blocks and push them.
while (areBlocksBeingGenerated) {
Option(blocksForPushing.poll(10, TimeUnit.MILLISECONDS)) match { case Some(block) => pushBlock(block) case None =>
}
} // At this point, state is StoppedGeneratingBlock. So drain the queue of to-be-pushed blocks.
logInfo("Pushing out the last " + blocksForPushing.size() + " blocks") while (!blocksForPushing.isEmpty) {
val block = blocksForPushing.take()
logDebug(s"Pushing block $block")
pushBlock(block)
logInfo("Blocks left to push " + blocksForPushing.size())
}
logInfo("Stopped block pushing thread")
} catch { case ie: InterruptedException =>
logInfo("Block pushing thread was interrupted") case e: Exception =>
reportError("Error in block pushing thread", e)
}
}从blocksForPushing队列中定时取出block然后pushBlock，代码如下
Option(blocksForPushing.poll(10, TimeUnit.MILLISECONDS)) match { case Some(block) => pushBlock(block) case None =>}接着看pushBlock(block)方法，代码如下
listener.onPushBlock(block.id, block.buffer)
这里调用了listener的onPushBlock方法，那么listener是从哪来的，查询一下listener变量，listener是在BlockGenerator实例化的时候传递进来的，找BlockGenerator的实例化，是通过createBlockGenerator方法接收的参数并传递给BlockGenerator。找createBlockGenerator方法的调用，终于看到了defaultBlockGeneratorListener的实例化，代码如下
private val defaultBlockGeneratorListener = new BlockGeneratorListener { def onAddData(data: Any, metadata: Any): Unit = { } def onGenerateBlock(blockId: StreamBlockId): Unit = { } def onError(message: String, throwable: Throwable) {
reportError(message, throwable)
} def onPushBlock(blockId: StreamBlockId, arrayBuffer: ArrayBuffer[_]) {
pushArrayBuffer(arrayBuffer, None, Some(blockId))
}
}原来onPushBlock方法在这里，看pushArrayBuffer的调用 ，pushArrayBuffer方法的代码如下
def pushArrayBuffer( arrayBuffer: ArrayBuffer[_], metadataOption: Option[Any], blockIdOption: Option[StreamBlockId]
) {
pushAndReportBlock(ArrayBufferBlock(arrayBuffer), metadataOption, blockIdOption)
}重磅性的一行代码出现了 pushAndReportBlock(ArrayBufferBlock(arrayBuffer), metadataOption, blockIdOption),代码如下
def pushAndReportBlock(
receivedBlock: ReceivedBlock,
metadataOption: Option[Any],
blockIdOption: Option[StreamBlockId]
) {
val blockId = blockIdOption.getOrElse(nextBlockId)
val time = System.currentTimeMillis
val blockStoreResult = receivedBlockHandler.storeBlock(blockId, receivedBlock)
logDebug(s"Pushed block $blockId in ${(System.currentTimeMillis - time)} ms")
val numRecords = blockStoreResult.numRecords
val blockInfo = ReceivedBlockInfo(streamId, numRecords, metadataOption, blockStoreResult)
trackerEndpoint.askWithRetry[Boolean](AddBlock(blockInfo))
logDebug(s"Reported block $blockId")
}这里面做了几事件事，第一调用receivedBlockHandler来存储block
第二向trackerEndpoint汇报block的存储结果blockInfo
receivedBlockHandler是在ReceiverSupervisorImpl实例化的时候创建的，代码如下
private val receivedBlockHandler: ReceivedBlockHandler = { if (WriteAheadLogUtils.enableReceiverLog(env.conf)) { if (checkpointDirOption.isEmpty) { throw new SparkException( "Cannot enable receiver write-ahead log without checkpoint directory set. " + "Please use streamingContext.checkpoint() to set the checkpoint directory. " + "See documentation for more details.")
} new WriteAheadLogBasedBlockHandler(env.blockManager, receiver.streamId,
receiver.storageLevel, env.conf, hadoopConf, checkpointDirOption.get)
} else { new BlockManagerBasedBlockHandler(env.blockManager, receiver.storageLevel)
}
}有两种类型，一种的WAL方式，还有一种普通的方式。WAL的方式以后再看，这里看BlockManagerBasedBlockHandler，代码如下
private[streaming] class BlockManagerBasedBlockHandler(
blockManager: BlockManager, storageLevel: StorageLevel)
extends ReceivedBlockHandler with Logging { def storeBlock(blockId: StreamBlockId, block: ReceivedBlock): ReceivedBlockStoreResult = {
var numRecords = None: Option[Long]
val putResult: Seq[(BlockId, BlockStatus)] = block match { case ArrayBufferBlock(arrayBuffer) =>
numRecords = Some(arrayBuffer.size.toLong)
blockManager.putIterator(blockId, arrayBuffer.iterator, storageLevel,tellMaster = true) case IteratorBlock(iterator) =>
val countIterator = new CountingIterator(iterator)
val putResult = blockManager.putIterator(blockId, countIterator, storageLevel,tellMaster = true)
numRecords = countIterator.count
putResult case ByteBufferBlock(byteBuffer) =>
blockManager.putBytes(blockId, byteBuffer, storageLevel, tellMaster = true) case o =>
throw new SparkException(
s"Could not store $blockId to block manager, unexpected block type ${o.getClass.getName}")
} if (!putResult.map { _._1 }.contains(blockId)) {
throw new SparkException(s"Could not store $blockId to block manager with storage level $storageLevel")
}
BlockManagerBasedStoreResult(blockId, numRecords)
} def cleanupOldBlocks(threshTime: Long) { // this is not used as blocks inserted into the BlockManager are cleared by DStream's clearing
// of BlockRDDs.
}
}这里就是借助BlockManager来存储block并返回block存储的元数据，终于看完了receiver的整个数据接收和存储。
整个过程还是很清晰的，如果有张流程图就最好了，流程图以后补上，谢谢
作者：海纳百川_spark
链接：https://www.jianshu.com/p/fd48919ad1ed
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