我的Java应用程序与服务器建立TCP连接，并通过发送和接收消息每秒与之通信。服务器和客户端都在同一台Mac上运行。在大约15-20分钟内，我的服务器崩溃并出现错误＆＃34; Errno :: EMFILE打开太多文件＆＃34;。这是我的客户代码：
package testtcp;
import java.awt.Dimension;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class TestTCP extends JPanel
{
JFrame frame = new JFrame("Button Demo");
ScheduledExecutorService executorService;
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream output = null;
private BufferedReader br = null;
private boolean isMapUpdating = false;
public TestTCP()
{
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setPreferredSize(new Dimension(300,300));
frame.add(this);
JButton b1 = new JButton("BLACK");
b1.setPreferredSize(new Dimension(150,50));
b1.setFocusPainted(false); // get rid of border around text
add(b1);
b1.addActionListener((java.awt.event.ActionEvent evt) ->
{
startAcarsConnection();
});
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public void startAcarsConnection()
{
start();
}
public void start()
{
System.out.println("THREAD START");
// Default timer rate
int timerRate = 1;
executorService = Executors.newSingleThreadScheduledExecutor();
executorService.scheduleAtFixedRate(new Runnable()
{
@Override
public void run()
{
// Create new TCP connection if the map is not currently updating
if(isMapUpdating == false)
{
isMapUpdating = true;
communicateWithServer();
}
}
}, 0, timerRate, TimeUnit.SECONDS);
}
public void stop()
{
executorService.shutdown();
}
public void communicateWithServer()
{
// Create a message to the server
String messageToServer = makeMessageToServer();
// Connect to the client and receive the response
String messageFromServer = connectToClient(messageToServer);
SwingUtilities.invokeLater(() ->
{
messageReceived(messageFromServer);
});
}
public String connectToClient(String messageToServer)
{
String data = "";
// Message from the server that should terminate TCP connection
String terminator = "END_IGOCONNECT_DATA";
try
{
// Create socket and streams
socket = new Socket("192.168.1.2", 7767);
input = new DataInputStream( socket.getInputStream());
output = new DataOutputStream( socket.getOutputStream());
//Send message to the server
output.writeBytes(messageToServer);
System.out.println("MESSAGE TO SERVER FROM CONNECT TO CLIENT: "+messageToServer);
//Read Response
br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
StringBuilder sb = new StringBuilder();
String s = "";
int value;
// Process the message from the server and add to the StringBuilder
while((value = br.read()) != -1)
{
// converts int to character
char c = (char)value;
sb.append(c);
if(sb.toString().contains(terminator))
{
break;
}
}
// Create the final string
data = sb.toString();
}
catch (UnknownHostException e)
{
System.out.println("Sock:"+e.getMessage());
// Close Connection
cancelConnection();
// Pop-up message that the airport was not found
String message = "Application was not able to establish connection with X-Plane.\n"
+ "Check whether IP Address and Port number were correctly entered in Settings.\n"
+ "Check whether connection is not being blocked by your firewall.";
JOptionPane.showMessageDialog(new JFrame(), message, "TCP Connection Error: UnknownHostException",
JOptionPane.ERROR_MESSAGE);
data = "ERROR";
}
catch (EOFException e)
{
System.out.println("EOF:"+e.getMessage());
// Close Connection
cancelConnection();
// Pop-up message that the airport was not found
String message = "Application was not able to establish connection with X-Plane.\n"
+ "Check whether IP Address and Port number were correctly entered in Settings.\n"
+ "Check whether connection is not being blocked by your firewall.";
JOptionPane.showMessageDialog(new JFrame(), message, "TCP Connection Error: EOFException",
JOptionPane.ERROR_MESSAGE);
data = "ERROR";
}
catch (IOException e)
{
System.out.println("IO:"+e.getMessage());
// Close Connection
cancelConnection();
// Pop-up message that the server was not found
if(!e.getMessage().equals("Socket closed"))
{
String message = "Application was not able to establish connection with X-Plane.\n"
+ "Check whether IP Address and Port number were correctly entered in Settings.\n"
+ "Check whether connection is not being blocked by your firewall.";
JOptionPane.showMessageDialog(new JFrame(), message, "TCP Connection Error: IOException",
JOptionPane.ERROR_MESSAGE);
}
// "Connection reset"
data = "ERROR";
}
finally
{
// TO DO!!! DISABLED FOR NOW!! closeSocketPax();
}
return data;
}
public void cancelConnection()
{
executorService.shutdown();
closeSocketPax();
SwingUtilities.invokeLater(() ->
{
System.out.println("Cancel Connection");
});
}
private void closeSocketPax()
{
try
{
if(socket!=null) { socket.close();}
if(input != null) { input.close();}
if(output != null) { output.close();}
if(br != null) { br.close();}
}
catch (IOException ex)
{
String message = "Error closing socket.";
JOptionPane.showMessageDialog(new JFrame(), message, "TCP Connection Error: IOException",
JOptionPane.ERROR_MESSAGE);
}
socket = null;
input = null;
output = null;
br = null;
}
private String makeMessageToServer()
{
return "MESSAGE TO SERVER";
}
private void messageReceived(String message)
{
System.out.println("MESSAGE RECEIVED: "+message);
isMapUpdating = false;
}
public static void main(String[] args)
{
new TestTCP();
}
}
我已经尝试解决这个问题差不多一个月了！ 有没有人在代码中看到问题并知道如何缓解这个问题？非常感谢！
答案 0 :(得分：1)
您创建的每个连接都使用文件描述符。在任何操作系统中，您的进程可以拥有的描述符数量都有限制。例如，在Linux环境中，我的限制是1024.不同的操作系统有不同的限制，但在Linux和Mac O / S等Unix派生环境中，您可以运行ulimit -n来查看限制是什么。
在您的代码中，您可以：
socket = new Socket("192.168.1.2", 7767);
connectToClient方法中的。每次执行此操作而不关闭套接字时，都会使用文件描述符。最终达到O / S定义的限制，你会在Mac O / S中得到Errno::EMFILE错误。
你有两个选择来解决这个问题。第一个是你已经注释掉的东西 - 当你完成它时关闭连接。但是，正如您在评论中指出的那样，这种情况非常频繁发生，并且您不希望产生持续打开和关闭的开销。
这带给我们第二选择 - 重用连接。如果您正在设计的协议处理它，套接字可以反复发送数据。通过协议来回发送数据并重用Socket。
虽然有警告 - 如果您的物理连接以某种方式被切断 - 例如，您从以太网切换到Wi-Fi - 您的服务仍然需要处理可能的错误。您的代码中包含大部分内容，但您可能需要考虑关闭并尝试重新连接。