一、UDP Server
项目的需要，需要利用java实现一个udp server，主要的功能是侦听来自客户端的udp请求，客户请求可能是大并发量的，对于每个请求Server端的处理很简单，处理每个请求的时间大约在1ms左右，但是Server端需要维护一个对立于请求的全局变量Cache，项目本身已经采用Mina架构（http://mina.apache.org/），我要开发的Server作为整个项目的一个模块，由于之前没有开发UDP Server，受TCP Server的影响，很自然的想利用多线程来实现，对于每个客户请求，新建一个线程来处理相应的逻辑，在实现的过程中，利用Mina的Thread Model，实现了一个多线程的UDP Server，但是由于要维护一个全局Cache，需要在各线程之间同步，加之处理请求的时间很短，很快就发现在此利用多线程，并不能提高性能，于是决定采用单线程来实现，在动手之前，还是发现有两种方案来实现单线程UDP Server：
1） 采用JDK的DatagramSocket和DatagramPacket来实现
public class UDPServerUseJDK extends Thread{
/**
* Constructor
* @param port port used to listen incoming connection
* @throws SocketException error to consturct a DatagramSocket with this port
*/
public MediatorServerUseJDK(int port) throws SocketException{
this("MediatorServerThread", port);
}
/**
* Constructor
* @param name the thread name
* @param port port used to listen incoming connection
* @throws SocketException error to consturct a DatagramSocket with this port
*/
public MediatorServerUseJDK(String name, int port) throws SocketException{
super(name);
socket = new DatagramSocket(port);
System.out.println("Mediator server started on JDK model...");
System.out.println("Socket buffer size: " + socket.getReceiveBufferSize());
}
public void run(){
long startTime = 0;
while(true){
try {
buf = new byte[1024];
// receive request
packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
.........
}catch (IOException e) {
.........
}
}
}
｝
2） 采用Mina的DatagramAcceptor来实现，在创建Exector的时候，只传递单个线程
public class MediatorServerUseMina {
private DatagramAcceptor acceptor;
public MediatorServerUseMina() {
}
public void startListener(InetSocketAddress address, IoHandler handler) {
// create an acceptor with a single thread
this.acceptor = new DatagramAcceptor(Executors.newSingleThreadExecutor());
// configure the thread models
DatagramAcceptorConfig acceptorConfig = acceptor.getDefaultConfig();
acceptorConfig.setThreadModel(ThreadModel.MANUAL);
// set the acceptor to reuse the address
acceptorConfig.getSessionConfig().setReuseAddress(true);
// add io filters
DefaultIoFilterChainBuilder filterChainBuilder = acceptor.getFilterChain();
// add CPU-bound job first,
filterChainBuilder.addLast("codec", new ProtocolCodecFilter(new StringCodecFactory()));
try {
// bind
acceptor.bind(address, handler);
System.out.println("Mediator Server started on mina model...");
System.out.println("Socket buffer size: " + acceptorConfig.getSessionConfig().getReceiveBufferSize());
} catch (IOException e) {
System.err.println("Error starting component listener on port(UDP) " + address.getPort() + ": "
+ e.getMessage());
}
}
}
二、Performance Test
为了测试两个Server的性能，写了个简单的测试客户端
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
/**
* @author Herry Hong
*
*/
public class PerformanceTest {
/** Number of threads to be created */
static final int THREADS = 100;
/** Packets to be sent per thread */
static final int PACKETS = 500;
/** The interval of two packets been sent for each thread */
private static final int INTERVAL = 80;
private static final String DATA = "5a76d93cb435fc54eba0b97156fe38f432a4e1da3a87cce8a222644466ed1317";
private class Sender implements Runnable {
private InetAddress address = null;
private DatagramSocket socket = null;
private String msg = null;
private String name = null;
private int packet_sent = 0;
public Sender(String addr, String msg, String name) throws SocketException,
UnknownHostException {
this.address = InetAddress.getByName(addr);
this.socket = new DatagramSocket();
this.msg = msg;
this.name = name;
}
@Override
public void run() {
// send request
byte[] buf = msg.getBytes();
DatagramPacket packet = new DatagramPacket(buf, buf.length,
address, 8000);
try {
for (int i = 0; i < PerformanceTest.PACKETS; i++) {
socket.send(packet);
packet_sent++;
Thread.sleep(INTERVAL);
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
//System.out.println("Thread " + name + " sends " + packet_sent + " packets.");
//System.out.println("Thread " + name + " end!");
}
}
/**
* @param args
*/
public static void main(String[] args) {
if (args.length != 1) {
System.out.println("Usage: java PerformanceTest <hostname>");
return;
}
String msg;
for (int i = 0; i < THREADS; i++) {
if(i % 2 == 0){
msg = i + "_" + (i+1) + ""r"n" + (i+1) + "_" + i + ""r"n" + DATA;
}else{
msg = i + "_" + (i-1) + ""r"n" + (i-1) + "_" + i + ""r"n" + DATA;
}
try {
new Thread(new PerformanceTest().new Sender(args[0], msg, "" + i)).start();
} catch (SocketException e) {
e.printStackTrace();
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
}
}
三、测试结果
测试环境：
Server：AMD Athlon(tm) 64 X2 Dual Core Processor 4000+，1G memory
Client：AMD Athlon(tm) 64 X2 Dual Core Processor 4000+，1G memory
在测试的过程中，当INTERVAL设置的太小时，服务器端会出现丢包现象，INTERVAL越小，丢包越严重，为了提高Server的性能，特将Socket的ReceiveBufferSize设置成默认大小的两倍，
对于JDK实现：
public MediatorServerUseJDK(String name, int port) throws SocketException{
super(name);
socket = new DatagramSocket(port);
// set the receive buffer size to double default size
socket.setReceiveBufferSize(socket.getReceiveBufferSize() * 2);
System.out.println("Mediator server started on JDK model...");
System.out.println("Socket buffer size: " + socket.getReceiveBufferSize());
}
对于Mina实现：
DatagramAcceptorConfig acceptorConfig = acceptor.getDefaultConfig();
acceptorConfig.setThreadModel(ThreadModel.MANUAL);
// set the acceptor to reuse the address
acceptorConfig.getSessionConfig().setReuseAddress(true);
// set the receive buffer size to double default size
int recBufferSize = acceptorConfig.getSessionConfig().getReceiveBufferSize();
acceptorConfig.getSessionConfig().setReceiveBufferSize(recBufferSize * 2);
此时，相同的INTERVAL，丢包现象明显减少。
接下来，再测试不同实现的性能差异：
UDP server started on JDK model...
Socket buffer size: 110592
INTERVAL ＝ 100ms，没有出现丢包，
Process time: 49988
Process time: 49982
Process time: 49984
Process time: 49986
Process time: 49984
INTERVAL ＝ 80ms，仍然没有丢包，不管Server是不是初次启动
Process time: 40006
Process time: 40004
Process time: 40003
Process time: 40005
Process time: 40013
UDP Server started on mina model...
Socket buffer size: 110592
INTERVAL ＝ 80ms，Server初次启动时，经常会出现丢包，当第一次（指服务器初次启动时）没有丢包时，随后基本不丢包，
Process time: 39973
Process time: 40006
Process time: 40007
Process time: 40008
Process time: 40008
INTERVAL ＝ 100ms，没有出现丢包
Process time: 49958
Process time: 49985
Process time: 49983
Process time: 49988
四、结论
在该要求下，采用JDK和Mina实现性能相当，但是在Server初次启动时JDK实现基本不会出现丢包，而Mina实现则在Server初次启动时经常出现丢包现象，在经历第一次测试后，两种实现处理时间相近，请求并发量大概为每ms一个请求时，服务器不会出现丢包。