Java多线程服务器*有时*在ServerSocket.accept()方法中抛出SocketException(套接字关闭)
我已经研究这个问题好几个小时了,但我无法找到一个合适的解决方案或解释为什么会抛出这个异常(java.net.SocketException:socketclosed)。我的最后一个方法是问你们 我为测试目的创建了一个简单的服务器客户端应用程序(“真实”应用程序使用相同的逻辑),请参见下文 如果我重复调用同一个测试用例(例如通过TestNG的invocationcount注释参数或使用简单的for循环),在某个点上会出现java.net.SocketException:socketclosed 下面的测试用例基本上只是启动服务器(打开服务器套接字),等待几毫秒,然后再次关闭套接字。关闭服务器套接字需要打开一个套接字,以便服务器从ServerSocket.accept()方法返回(请参阅server#shutdown() 我认为这可能是ServerSocket.accept()行后面的代码的多线程问题。所以我暂时用一个同步块来包围它——也没用 你知道为什么会抛出这个异常吗 最好的, 克里斯 Server.java如下所示:Java多线程服务器*有时*在ServerSocket.accept()方法中抛出SocketException(套接字关闭),java,multithreading,exception,Java,Multithreading,Exception,我已经研究这个问题好几个小时了,但我无法找到一个合适的解决方案或解释为什么会抛出这个异常(java.net.SocketException:socketclosed)。我的最后一个方法是问你们 我为测试目的创建了一个简单的服务器客户端应用程序(“真实”应用程序使用相同的逻辑),请参见下文 如果我重复调用同一个测试用例(例如通过TestNG的invocationcount注释参数或使用简单的for循环),在某个点上会出现java.net.SocketException:socketclosed 下
package multithreading;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import org.apache.log4j.Logger;
public class Server {
private ServerSocket serverSocket;
private boolean isShuttingDown;
private final static Logger logger = Logger.getLogger(Server.class);
public void start() throws Exception {
try {
serverSocket = new ServerSocket(5000);
isShuttingDown = false;
} catch (Exception e) {
throw new RuntimeException("Starting up the server failed - aborting", e);
}
while (true) {
try {
Socket socket = serverSocket.accept();
if (!isShuttingDown) {
new Thread(new EchoRequestHandler(socket)).start();
} else {
logger.info("Server is going to shutdown");
break;
}
} catch (IOException e) {
logger.error("Error occured while waiting for new connections, stopping server", e);
throw e;
}
}
}
public synchronized boolean isRunning() {
if (serverSocket != null && serverSocket.isBound() && !serverSocket.isClosed() && !isShuttingDown) {
return true;
}
return false;
}
public synchronized void shutdown() throws IOException {
if (isRunning()) {
isShuttingDown = true;
if (serverSocket != null && !serverSocket.isClosed()) {
try {
/*
* since the server socket is still waiting in it's accept()
* method, just closing the server socket would cause an
* exception to be thrown. By quickly opening a socket
* (connection) to the server socket and immediately closing
* it again, the server socket's accept method will return
* and since the isShuttingDown flag is then false, the
* socket will be closed.
*/
new Socket(serverSocket.getInetAddress(), serverSocket.getLocalPort()).close();
serverSocket.close();
} catch (IOException e) {
logger.error("Closing the server socket has failed - aborting now.", e);
throw e;
}
}
} else {
throw new IOException("Server socket is already closed which should not be the case.");
}
}
}
测试类执行以下操作:
package multithreading;
import java.io.IOException;
import org.testng.annotations.Test;
public class Testing {
// @Test(invocationCount=10, skipFailedInvocations=true)
@Test
public void loadTest() throws InterruptedException, IOException {
for (int i = 0; i < 10; i++) {
final Server s = new Server();
new Thread(new Runnable() {
@Override
public void run() {
try {
s.start();
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
Thread.sleep(500);
gracefullyShutdownServer(s);
Thread.sleep(1000);
}
}
private void gracefullyShutdownServer(final Server server) throws InterruptedException {
try {
server.shutdown();
while (server.isRunning()) {
Thread.sleep(500);
}
} catch (IOException e) {
System.err.println(e);
}
}
}
如本链接中所述,打开一个插座以关闭另一个插座是错误的。在套接字上调用close应该通过抛出一个可以安全捕获和忽略的异常来取消“接受”。J.N.关于处理关闭的方式是正确的 至于这不起作用的原因,我认为竞争在于您的服务器代码读取
isShuttingDown
时没有同步。我不明白为什么值更改应该立即对服务器线程可见。所以很有可能再进行一轮
正如J.N.所说:在接受时处理服务器中的异常。如果您想知道您的代码在套接字上执行close
操作是否可能引发异常,请将isShuttingDown
放在周围,确保安全访问它。(一个synchronized(这个){}
块,或者编写一个非常短的同步访问器。)
在这个特定的例子中,我认为使
isShuttingDown
volatile就足够了,这在developerWorks文章中有详细介绍。但是要小心,这不是一个灵丹妙药。提供困扰您的异常的堆栈跟踪会很好。@Mat:刚刚添加了堆栈跟踪(很抱歉没有首先发布它,我真蠢)给出的链接不再有效,不过感谢您提供的信息:)
ERROR 2011-03-13 16:14:23,537 [Thread-6] multithreading.Server: Error occured while waiting for new connections, stopping server
java.net.SocketException: Socket closed
at java.net.PlainSocketImpl.socketAccept(Native Method)
at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:390)
at java.net.ServerSocket.implAccept(ServerSocket.java:453)
at java.net.ServerSocket.accept(ServerSocket.java:421)
at multithreading.Server.start(Server.java:26)
at multithreading.Testing$1.run(Testing.java:18)
at java.lang.Thread.run(Thread.java:680)
java.net.SocketException: Socket closed
at java.net.PlainSocketImpl.socketAccept(Native Method)
at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:390)
at java.net.ServerSocket.implAccept(ServerSocket.java:453)
at java.net.ServerSocket.accept(ServerSocket.java:421)
at multithreading.Server.start(Server.java:26)
at multithreading.Testing$1.run(Testing.java:18)
at java.lang.Thread.run(Thread.java:680)