【Kafka源码】SocketServer启动过程
SocketServer主要用于接收外部的网络请求，并把请求添加到请求队列中。
一、入口
在KafkaServer.scala中的start方法中，有这样的入口：
socketServer = new SocketServer(config, metrics, kafkaMetricsTime)
socketServer.startup()
这块就是启动了一个SocketServer，我们具体看一下。
二、构造方法
我们看下SocketServer里面包含的参数：
private val endpoints = config.listeners
private val numProcessorThreads = config.numNetworkThreads
private val maxQueuedRequests = config.queuedMaxRequests
private val totalProcessorThreads = numProcessorThreads * endpoints.siz
private val maxConnectionsPerIp = config.maxConnectionsPerIp
private val maxConnectionsPerIpOverrides config.maxConnectionsPerIpOverride
this.logIdent = "[Socket Server on Broker " + config.brokerId + "], "
val requestChannel = new RequestChannel(totalProcessorThreadsmaxQueuedRequests)
private val processors = new Array[Processor](totalProcessorThreads)
private[network] val acceptors = mutable.Map[EndPoint, Acceptor]()
private var connectionQuotas: ConnectionQuotas = _
这里面涉及几个配置内容：
- listeners：默认是PLAINTEXT://:port,前面部分是协议,可配置为PLAINTEXT,SSL,SASL_PLAINTEXT,SASL_SSL
- num.network.threads：处理网络请求的线程个数配置,默认是3
- queued.max.requests：请求队列的最大个数,默认500
- max.connections.per.ip：单机IP的最大连接个数的配置,默认不限制
- max.connections.per.ip.overrides：针对某个特别的IP的连接个数限制的重新设置值.多个IP配置间使用逗号分开,如:host1:500,host2:600
三、启动SocketServer
启动的代码如下：
/**
* Start the socket server
*/
def startup() {
this.synchronized {
//每个ip的连接数限制
connectionQuotas = new ConnectionQuotas(maxConnectionsPerIp, maxConnectionsPerIpOverrides)
val sendBufferSize = config.socketSendBufferBytes
val recvBufferSize = config.socketReceiveBufferBytes
val brokerId = config.brokerId
//这里根据每一个endpoint(也就是配置的listener的协议与端口),生成处理的网络线程Processor与Acceptor实例.并启动endpoint对应的Acceptor实例.在生成Acceptor的实例时,会同时启动此实例中对应的线程处理实例数组Processor.
var processorBeginIndex = 0
endpoints.values.foreach { endpoint =>
val protocol = endpoint.protocolType
val processorEndIndex = processorBeginIndex + numProcessorThreads
for (i <- processorBeginIndex until processorEndIndex)
processors(i) = newProcessor(i, connectionQuotas, protocol)
val acceptor = new Acceptor(endpoint, sendBufferSize, recvBufferSize, brokerId,
processors.slice(processorBeginIndex, processorEndIndex), connectionQuotas)
acceptors.put(endpoint, acceptor)
Utils.newThread("kafka-socket-acceptor-%s-%d".format(protocol.toString, endpoint.port), acceptor, false).start()
acceptor.awaitStartup()
processorBeginIndex = processorEndIndex
}
}
newGauge("NetworkProcessorAvgIdlePercent",
new Gauge[Double] {
def value = allMetricNames.map( metricName =>
metrics.metrics().get(metricName).value()).sum / totalProcessorThreads
}
)
info("Started " + acceptors.size + " acceptor threads")
}
这块涉及到几个配置项，主要用于生成socket中的SO_SNDBUF和SO_RCVBUF。
- socket.send.buffer.bytes：默认值100kb,这个用于SOCKET发送数据的缓冲区大小
- socket.receive.buffer.bytes：默认值100kb,这个用于SOCKET的接收数据的缓冲区大小
- broker.id
3.1 newProcessor
我们先看下这个简单的赋值。
protected[network] def newProcessor(id: Int, connectionQuotas: ConnectionQuotas, protocol: SecurityProtocol): Processor = {
new Processor(id,
time,
config.socketRequestMaxBytes,
requestChannel,
connectionQuotas,
config.connectionsMaxIdleMs,
protocol,
config.values,
metrics
)
}
其实就是Processor的实例生成，主要涉及几个配置项：
- socket.request.max.bytes：设置每次请求的数据大小.默认值,100MB
- connections.max.idle.ms：默认为10分钟,用于设置每个连接最大的空闲回收时间
3.2 Acceptor
每个endPoint对应一个Acceptor，也就是每个listener对应一个Acceptor。Acceptor主要用于接收网络请求，将请求分发到processor处理。我们来看下Acceptor的run方法：
def run() {
//将channel注册到selector上
serverChannel.register(nioSelector, SelectionKey.OP_ACCEPT)
startupComplete()
try {
var currentProcessor = 0
while (isRunning) {
try {
//这里进行堵塞接收,最多等500ms,如果ready返回的值是0表示还没有准备好,否则表示准备就绪.表示有通道已经被注册
val ready = nioSelector.select(500)
if (ready > 0) {
//这里得到已经准备好的网络通道的key的集合
val keys = nioSelector.selectedKeys()
val iter = keys.iterator()
while (iter.hasNext && isRunning) {
try {
val key = iter.next
iter.remove()
//如果selectkey已经注册到accept事件,通过accept函数与对应的线程Processor进行处理.这里表示这个socket的通道包含有一个client端的连接请求.
if (key.isAcceptable)
accept(key, processors(currentProcessor))
else
throw new IllegalStateException("Unrecognized key state for acceptor thread.")
// round robin to the next processor thread
//每次接收一个socket请求后,用于处理的线程进行轮询到一个线程中处理.
currentProcessor = (currentProcessor + 1) % processors.length
} catch {
case e: Throwable => error("Error while accepting connection", e)
}
}
}
}
catch {
// We catch all the throwables to prevent the acceptor thread from exiting on exceptions due
// to a select operation on a specific channel or a bad request. We don't want the
// the broker to stop responding to requests from other clients in these scenarios.
case e: ControlThrowable => throw e
case e: Throwable => error("Error occurred", e)
}
}
} finally {
debug("Closing server socket and selector.")
swallowError(serverChannel.close())
swallowError(nioSelector.close())
shutdownComplete()
}
}
下面我们看下accept方法：
/*
* Accept a new connection
*/
def accept(key: SelectionKey, processor: Processor) {
val serverSocketChannel = key.channel().asInstanceOf[ServerSocketChannel]
//得到请求的socket通道
val socketChannel = serverSocketChannel.accept()
try {
//这里检查当前的IP的连接数是否已经达到了最大的连接数,如果是,直接throw too many connect.
connectionQuotas.inc(socketChannel.socket().getInetAddress)
socketChannel.configureBlocking(false)
socketChannel.socket().setTcpNoDelay(true)
socketChannel.socket().setKeepAlive(true)
socketChannel.socket().setSendBufferSize(sendBufferSize)
debug("Accepted connection from %s on %s and assigned it to processor %d, sendBufferSize [actual|requested]: [%d|%d] recvBufferSize [actual|requested]: [%d|%d]"
.format(socketChannel.socket.getRemoteSocketAddress, socketChannel.socket.getLocalSocketAddress, processor.id,
socketChannel.socket.getSendBufferSize, sendBufferSize,
socketChannel.socket.getReceiveBufferSize, recvBufferSize))
//对应的processor处理socket通道
processor.accept(socketChannel)
} catch {
case e: TooManyConnectionsException =>
info("Rejected connection from %s, address already has the configured maximum of %d connections.".format(e.ip, e.count))
close(socketChannel)
}
}
3.3 Processor
上面accept方法中，调用到了processor的accept方法，我们看下这个accept方法：
/**
* Queue up a new connection for reading
*/
def accept(socketChannel: SocketChannel) {
newConnections.add(socketChannel)
wakeup()
}
其实就是向队列中新增了一个socket通道，等待processor线程处理。下面我们看下processor是怎么处理的。
override def run() {
startupComplete()
while (isRunning) {
try {
// setup any new connections that have been queued up
configureNewConnections()
// register any new responses for writing
processNewResponses()
poll()
processCompletedReceives()
processCompletedSends()
processDisconnected()
} catch {
// We catch all the throwables here to prevent the processor thread from exiting. We do this because
// letting a processor exit might cause a bigger impact on the broker. Usually the exceptions thrown would
// be either associated with a specific socket channel or a bad request. We just ignore the bad socket channel
// or request. This behavior might need to be reviewed if we see an exception that need the entire broker to stop.
case e: ControlThrowable => throw e
case e: Throwable =>
error("Processor got uncaught exception.", e)
}
}
debug("Closing selector - processor " + id)
swallowError(closeAll())
shutdownComplete()
}
这块其实是个门面模式，里面调用的内容比较多，我们一一看一下。
3.3.1 configureNewConnections
这块是从队列中取一个连接，并注册到selector上。
/**
* Register any new connections that have been queued up
*/
private def configureNewConnections() {
while (!newConnections.isEmpty) {
val channel = newConnections.poll()
try {
debug(s"Processor $id listening to new connection from ${channel.socket.getRemoteSocketAddress}")
val localHost = channel.socket().getLocalAddress.getHostAddress
val localPort = channel.socket().getLocalPort
val remoteHost = channel.socket().getInetAddress.getHostAddress
val remotePort = channel.socket().getPort
val connectionId = ConnectionId(localHost, localPort, remoteHost, remotePort).toString
selector.register(connectionId, channel)
} catch {
// We explicitly catch all non fatal exceptions and close the socket to avoid a socket leak. The other
// throwables will be caught in processor and logged as uncaught exceptions.
case NonFatal(e) =>
// need to close the channel here to avoid a socket leak.
close(channel)
error(s"Processor $id closed connection from ${channel.getRemoteAddress}", e)
}
}
}
3.3.2 processNewResponses
private def processNewResponses() {
var curr = requestChannel.receiveResponse(id)
while (curr != null) {
try {
curr.responseAction match {
case RequestChannel.NoOpAction =>
// There is no response to send to the client, we need to read more pipelined requests
// that are sitting in the server's socket buffer
curr.request.updateRequestMetrics
trace("Socket server received empty response to send, registering for read: " + curr)
selector.unmute(curr.request.connectionId)
case RequestChannel.SendAction =>
sendResponse(curr)
case RequestChannel.CloseConnectionAction =>
curr.request.updateRequestMetrics
trace("Closing socket connection actively according to the response code.")
close(selector, curr.request.connectionId)
}
} finally {
curr = requestChannel.receiveResponse(id)
}
}
}
3.3.3 poll
private def poll() {
try selector.poll(300)
catch {
case e @ (_: IllegalStateException | _: IOException) =>
error(s"Closing processor $id due to illegal state or IO exception")
swallow(closeAll())
shutdownComplete()
throw e
}
}
@Override
public void poll(long timeout) throws IOException {
if (timeout < 0)
throw new IllegalArgumentException("timeout should be >= 0");
clear();
if (hasStagedReceives() || !immediatelyConnectedKeys.isEmpty())
timeout = 0;
/* check ready keys */
long startSelect = time.nanoseconds();
int readyKeys = select(timeout);
long endSelect = time.nanoseconds();
currentTimeNanos = endSelect;
this.sensors.selectTime.record(endSelect - startSelect, time.milliseconds());
if (readyKeys > 0 || !immediatelyConnectedKeys.isEmpty()) {
pollSelectionKeys(this.nioSelector.selectedKeys(), false);
pollSelectionKeys(immediatelyConnectedKeys, true);
}
addToCompletedReceives();
long endIo = time.nanoseconds();
this.sensors.ioTime.record(endIo - endSelect, time.milliseconds());
maybeCloseOldestConnection();
}
这块主要看一下pollSelectionKeys方法：
private void pollSelectionKeys(Iterable<SelectionKey> selectionKeys, boolean isImmediatelyConnected) {
Iterator<SelectionKey> iterator = selectionKeys.iterator();
while (iterator.hasNext()) {
SelectionKey key = iterator.next();
iterator.remove();
KafkaChannel channel = channel(key);
// register all per-connection metrics at once
sensors.maybeRegisterConnectionMetrics(channel.id());
lruConnections.put(channel.id(), currentTimeNanos);
try {
/* complete any connections that have finished their handshake (either normally or immediately) */
if (isImmediatelyConnected || key.isConnectable()) {
if (channel.finishConnect()) {
this.connected.add(channel.id());
this.sensors.connectionCreated.record();
} else
continue;
}
/* if channel is not ready finish prepare */
if (channel.isConnected() && !channel.ready())
channel.prepare();
/* if channel is ready read from any connections that have readable data */
if (channel.ready() && key.isReadable() && !hasStagedReceive(channel)) {
NetworkReceive networkReceive;
while ((networkReceive = channel.read()) != null)
addToStagedReceives(channel, networkReceive);
}
/* if channel is ready write to any sockets that have space in their buffer and for which we have data */
if (channel.ready() && key.isWritable()) {
Send send = channel.write();
if (send != null) {
this.completedSends.add(send);
this.sensors.recordBytesSent(channel.id(), send.size());
}
}
/* cancel any defunct sockets */
if (!key.isValid()) {
close(channel);
this.disconnected.add(channel.id());
}
} catch (Exception e) {
String desc = channel.socketDescription();
if (e instanceof IOException)
log.debug("Connection with {} disconnected", desc, e);
else
log.warn("Unexpected error from {}; closing connection", desc, e);
close(channel);
this.disconnected.add(channel.id());
}
}
}
这里开始处理socket通道中的请求,根据如下几个流程进行处理:
- 如果请求中包含有一个isConnectable操作,把这个连接缓存起来.
- 如果请求中包含有isReadable操作.表示这个client的管道中包含有数据,需要读取,接收数据.
- 如果包含有isWriteable的操作,表示需要向client端进行写操作.
- 最后检查是否有connect被关闭的请求或connect连接空闲过期
3.3.4 processCompletedReceives
得到对应的请求的Request的实例,并把这个Request通过SocketServer中的RequestChannel的sendRequest的函数,把请求添加到请求的队列中.等待KafkaApis来进行处理.
private def processCompletedReceives() {
selector.completedReceives.asScala.foreach { receive =>
try {
val channel = selector.channel(receive.source)
val session = RequestChannel.Session(new KafkaPrincipal(KafkaPrincipal.USER_TYPE, channel.principal.getName),
channel.socketAddress)
val req = RequestChannel.Request(processor = id, connectionId = receive.source, session = session, buffer = receive.payload, startTimeMs = time.milliseconds, securityProtocol = protocol)
//这是重点！！！可以看下KafkaApis对消息的处理，后续会分析到
requestChannel.sendRequest(req)
selector.mute(receive.source)
} catch {
case e @ (_: InvalidRequestException | _: SchemaException) =>
// note that even though we got an exception, we can assume that receive.source is valid. Issues with constructing a valid receive object were handled earlier
error(s"Closing socket for ${receive.source} because of error", e)
close(selector, receive.source)
}
}
}
3.3.5 processCompletedSends
这里的send完成表示有向client端进行响应的写操作处理完成
private def processCompletedSends() {
selector.completedSends.asScala.foreach { send =>
val resp = inflightResponses.remove(send.destination).getOrElse {
throw new IllegalStateException(s"Send for ${send.destination} completed, but not in `inflightResponses`")
}
resp.request.updateRequestMetrics()
selector.unmute(send.destination)
}
}
3.3.6 processDisconnected
如果socket server中包含有已经关闭的连接,减少这个quotas中对此ip的连接数的值.
这个情况包含connect处理超时或者说有connect的消息处理错误被发起了close的请求后的处理成功的消息.
private def processDisconnected() {
selector.disconnected.asScala.foreach { connectionId =>
val remoteHost = ConnectionId.fromString(connectionId).getOrElse {
throw new IllegalStateException(s"connectionId has unexpected format: $connectionId")
}.remoteHost
inflightResponses.remove(connectionId).foreach(_.request.updateRequestMetrics())
// the channel has been closed by the selector but the quotas still need to be updated
connectionQuotas.dec(InetAddress.getByName(remoteHost))
}
}
