简单的Scala TCP服务器中的套接字问题

Question

我是Scala的新手所以问题可能很简单,尽管我花了一些时间来解决它.我有一个简单的Scala TCP服务器(没有actor,单线程):

import java.io._
import java.net._

object Application {
  def readSocket(socket: Socket): String = {
    val bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream))
    var request = ""
    var line = ""
    do {
      line = bufferedReader.readLine()
      if (line == null) {
        println("Stream terminated")
        return request
      }
      request += line + "\n"
    } while (line != "")
    request
  }

  def writeSocket(socket: Socket, string: String) {
    val out: PrintWriter = new PrintWriter(new OutputStreamWriter(socket.getOutputStream))
    out.println(string)
    out.flush()
  }

  def main(args: Array[String]) {
    val port = 8000
    val serverSocket = new ServerSocket(port)
    while (true) {
      val socket = serverSocket.accept()
      readSocket(socket)
      writeSocket(socket, "HTTP/1.1 200 OK\r\n\r\nOK")
      socket.close()
    }
  }
}

服务器侦听命令localhost:8000请求并OK在正文中发送带有单个字的HTTP响应.然后我像这样运行Apache Benchmark:

ab -c 1000 -n 10000 http://localhost:8000/

这是第一次很好用.我第二次启动ab它挂起产生以下输出netstat -a | grep 8000:

....
tcp        0      0 localhost.localdo:43709 localhost.localdom:8000 FIN_WAIT2  
tcp        0      0 localhost.localdo:43711 localhost.localdom:8000 FIN_WAIT2  
tcp        0      0 localhost.localdo:43717 localhost.localdom:8000 FIN_WAIT2  
tcp        0      0 localhost.localdo:43777 localhost.localdom:8000 FIN_WAIT2  
tcp        0      0 localhost.localdo:43722 localhost.localdom:8000 FIN_WAIT2  
tcp        0      0 localhost.localdo:43725 localhost.localdom:8000 FIN_WAIT2  
tcp6       0      0 [::]:8000               [::]:*                  LISTEN     
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43724 CLOSE_WAIT 
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43786 CLOSE_WAIT 
tcp6       1      0 localhost.localdom:8000 localhost.localdo:43679 CLOSE_WAIT 
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43735 CLOSE_WAIT 
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43757 CLOSE_WAIT 
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43754 CLOSE_WAIT 
tcp6      83      0 localhost.localdom:8000 localhost.localdo:43723 CLOSE_WAIT
....

由于服务器不再提供请求.还有一个细节:ab具有相同参数的相同脚本可以在同一台机器上平稳地测试一个简单的Node.js服务器.所以这个问题与我设置为可重用的多个已打开的TCP连接无关

sudo sysctl -w net.ipv4.tcp_tw_recycle=1
sudo sysctl -w net.ipv4.tcp_tw_reuse=1

谁能给我一个我错过的线索？

编辑:流处理的终止已添加到上面的代码中:

    if (line == null) {
      println("Stream terminated")
      return request
    }

Answer 1

我正在为那些有一天会偶然发现同一问题的人发布我自己的问题的（部分）答案。首先，问题的本质不在于源代码，而在于系统本身，它限制了众多的连接。问题是socket传递给readSocket函数的在某些情况下会出现损坏，即无法读取并且在第一次调用时bufferedReader.readLine()返回null或无限期挂起。以下两个步骤使代码可以在某些机器上运行：

1. 增加套接字的并发连接数

   sysctl -w net.core.somaxconn=65535
   

2. 向构造函数提供第二个参数，ServerSocket该参数将显式设置连接队列的长度：

   val maxQueue = 50000
   val serverSocket = new ServerSocket(port, maxQueue)
   

上述步骤解决了 EC2 m1.large 实例上的问题，但我在本地计算机上仍然遇到问题。更好的方法是使用Akka来处理此类事情：

import akka.actor._
import java.net.InetSocketAddress
import akka.util.ByteString

class TCPServer(port: Int) extends Actor {

  override def preStart {
    IOManager(context.system).listen(new InetSocketAddress(port))
  }

  def receive = {
    case IO.NewClient(server) =>
      server.accept()
    case IO.Read(rHandle, bytes) => {
      val byteString = ByteString("HTTP/1.1 200 OK\r\n\r\nOK")
      rHandle.asSocket.write(byteString)
      rHandle.close()
    }
  }
}

object Application {
  def main(args: Array[String]) {
    val port = 8000
    ActorSystem().actorOf(Props(new TCPServer(port)))
  }
}