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Java Jetty WebSocket服務器：使用異步斷開客戶端的方式處理廣播

[英]Java Jetty WebSocket Server: Handle broadcasts with asynchronously disconnecting clients

 原文  2014-04-17 15:59:37  5   1    java/ asynchronous/ websocket/ jetty

問題描述

背景

我正在研究一個概念證明，其中包括使用websocket通信的服務器-客戶端系統。 我使用了一個小型碼頭解決方案（jetty-all-9.1.3.v20140225.jar和servlet-api-3.1.jar）。 我具有PoC的大部分基本功能。

我有2節課：

  • TestServer（具有創建服務器實例的主要功能，請參見代碼）
  • ClientSocket（為每個客戶端實例化的WebSocket對象）

問題

我想討論的問題與廣播客戶端斷開連接有關。 服務器將所有ClientSockets實例保存在一個陣列中，並將ClientSockets的“ onConnect”功能添加到該陣列中。

該系統稍后將限制廣播到客戶端組，但是對於PoC，所有連接的客戶端都將獲得廣播。 如果一個客戶端斷開連接，我想向所有其他客戶端發送通知（“ myClient已斷開連接。”或類似的消息）。

為此，我在服務器中實現了廣播功能，該功能遍歷客戶端列表，並將此信息發送給所有已連接的客戶端（斷開連接的客戶端除外）。 此功能還用於向所有客戶端通知其他事情，例如新連接，並且在客戶端與某人連接或廣播某物的同時斷開連接的情況下，也很可能在此發生此問題。

通過連接多個（10+）個客戶端（我在js中完成），然后同時斷開它們的連接，很容易產生此問題。 如果這樣做，我總是會遇到並發錯誤，對於很少的客戶端（2-3），有時它會起作用，具體取決於我猜測的時間。

問題

考慮到任何客戶端都可以隨時（異步）斷開連接，我應該如何處理向所有其他客戶端廣播的任務？ 我可以這樣做而不會產生異常嗎？ 由於它是異步的，除了處理發生的異常外，我看不到其他任何方式。 任何建議，不勝感激。

碼

TestServer.java 

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.websocket.server.WebSocketHandler;
import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;

public class TestServer {
    private static final TestServer testServer = new TestServer();
    private ArrayList<ClientSocket> clients = new ArrayList<>();

    public static void main(String[] args) throws Exception {
        int port = 8080;
        Server server = new Server(port);
        WebSocketHandler wsHandler = new WebSocketHandler() {
            @Override
            public void configure(WebSocketServletFactory factory) {
                factory.register(ClientSocket.class);
            }
        };
        server.setHandler(wsHandler);
        System.out.println("Starting server on port " + port + ".");
        server.start();
        server.join();
    }

    public static TestServer getServer() {
        return testServer;
    }

    public void addClient(ClientSocket client) {
        this.clients.add(client);
    }

    public void removeClient(ClientSocket client) {
        this.clients.remove(client);
        this.broadcast("disconnect " + client.id, client);  
    }

    public void broadcast(String message, ClientSocket excludedClient) {
        log("Sending to all clients: " + message);
        for (ClientSocket cs : this.clients) {
            if (!cs.equals(excludedClient) && cs.session.isOpen() && cs != null) {
                try {
                    cs.session.getRemote().sendStringByFuture(message);
                } catch (Exception e) {
                    log("Error when broadcasting to " + cs.id + " (" + cs.address + "):");
                    log(e.getMessage());
                }
            }
        }
    }

由於如果您在過程中混入數組，以這種方式循環遍歷通常不起作用，所以我也嘗試了以下廣播功能： 

    public void broadcast(String message, ClientSocket excludedClient) {
        log("Sending to all clients: " + message);
        Iterator<ClientSocket> cs = this.clients.iterator();
        while (cs.hasNext()) {
            ClientSocket client = cs.next();
            if (client != null) {
                if (!client.equals(excludedClient) && client.session.isOpen()) {
                try {
                    client.session.getRemote().sendStringByFuture(message);
                } catch (Exception e) {
                    log("Error when broadcasting to " + client.id + " (" + client.address + "):");
                    log(e.getMessage());
                }
            }
        }
    }

但是，它沒有任何更好的效果，因為問題是，如果另一個ClientSocket對象在第一個廣播其斷開連接時斷開連接，則該陣列可以被異步地干預。

ClientSocket.java 

import java.io.IOException;
import org.eclipse.jetty.websocket.api.Session;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
import org.eclipse.jetty.websocket.api.annotations.WebSocket;

@WebSocket(maxIdleTime=0)
public class ClientSocket {
    TestServer server = TestServer.getServer();
    Session session;
    String id;
    String address;

    @OnWebSocketClose
    public void onClose(Session session, int statusCode, String reason) {
        server.log("Disconnected: " + this.id + "(" + this.address + ")" + " (statusCode=" + statusCode + ", reason=" + reason + ")");
        server.removeClient(this);
    }

    @OnWebSocketError
    public void onError(Session session, Throwable t) {
        server.log(this.id + "(" + this.address + ") error: " + t.getMessage());
    }

    @OnWebSocketConnect
    public void onConnect(Session session) {
        this.session = session;
        this.address = this.session.getRemoteAddress().getAddress().toString().substring(1);
        this.id = this.address; //Until user is registered their id is their IP
        server.log("New connection: " + this.address);
        server.addClient(this);
        try {
            session.getRemote().sendString("Hello client with address " + this.address + "!");
        } catch (IOException e) {
            server.log("Error in onConnect for " + this.id + "(" + this.address + "): " + e.getMessage());
        }
    }

    @OnWebSocketMessage
    public void onMessage(Session session, String message) {
        server.log("Received from " + this.id + "(" + this.address + "): " + message);
        String replyMessage;
        String[] commandList = message.split("\\s+");
        switch (commandList[0].toLowerCase()) {
            case "register":
                if (commandList.length > 1) {
                    this.id = commandList[1];
                    replyMessage = "Registered on server as " + this.id;
                    server.broadcast(this.id + " has connected", this);
                } else {
                    replyMessage = "Incorrect register message";
                }
                break;
            default:
                replyMessage = "echo " + message;
                break;
        }
        server.log("Sending to " + this.id + "(" + this.address + "): " + replyMessage);
        try {
            session.getRemote().sendString(replyMessage);
        } catch (IOException e) {
            server.log("Error during reply in onMessage for " + this.id + "(" + this.address + "): " + e.getMessage());
        }
    }
}

我粘貼了整個類是為了保持完整性，即使我刪除了onMessage開關中的某些情況。 但是需要注意的部分是onConnect和onClose函數，這些函數將填充服務器中的客戶端陣列並從中刪除客戶端。

錯誤記錄 

[2014-04-17 17:40:17.961] Sending to all clients: disconnect testclient4
2014-04-17 17:40:17.962:WARN:ClientSocket:qtp29398564-17: Unhandled Error (closing connection)
org.eclipse.jetty.websocket.api.WebSocketException: Cannot call method public void ClientSocket#onClose(org.eclipse.jetty.websocket.api.Session, int, java.lang.String) with args: [org.eclipse.jetty.websocket.common.WebSocketSession, java.lang.Integer, <null>]
        at org.eclipse.jetty.websocket.common.events.annotated.CallableMethod.call(CallableMethod.java:99)
        at org.eclipse.jetty.websocket.common.events.annotated.OptionalSessionCallableMethod.call(OptionalSessionCallableMethod.java:68)
        at org.eclipse.jetty.websocket.common.events.JettyAnnotatedEventDriver.onClose(JettyAnnotatedEventDriver.java:122)
        at org.eclipse.jetty.websocket.common.events.AbstractEventDriver.incomingFrame(AbstractEventDriver.java:125)
        at org.eclipse.jetty.websocket.common.WebSocketSession.incomingFrame(WebSocketSession.java:302)
        at org.eclipse.jetty.websocket.common.extensions.AbstractExtension.nextIncomingFrame(AbstractExtension.java:163)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.nextIncomingFrame(PerMessageDeflateExtension.java:92)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.incomingFrame(PerMessageDeflateExtension.java:66)
        at org.eclipse.jetty.websocket.common.extensions.ExtensionStack.incomingFrame(ExtensionStack.java:210)
        at org.eclipse.jetty.websocket.common.Parser.notifyFrame(Parser.java:219)
        at org.eclipse.jetty.websocket.common.Parser.parse(Parser.java:257)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.read(AbstractWebSocketConnection.java:500)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.onFillable(AbstractWebSocketConnection.java:409)
        at org.eclipse.jetty.io.AbstractConnection$1.run(AbstractConnection.java:505)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
        at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
        at java.lang.Thread.run(Thread.java:744)
Caused by:
java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.eclipse.jetty.websocket.common.events.annotated.CallableMethod.call(CallableMethod.java:71)
        at org.eclipse.jetty.websocket.common.events.annotated.OptionalSessionCallableMethod.call(OptionalSessionCallableMethod.java:68)
        at org.eclipse.jetty.websocket.common.events.JettyAnnotatedEventDriver.onClose(JettyAnnotatedEventDriver.java:122)
        at org.eclipse.jetty.websocket.common.events.AbstractEventDriver.incomingFrame(AbstractEventDriver.java:125)
        at org.eclipse.jetty.websocket.common.WebSocketSession.incomingFrame(WebSocketSession.java:302)
        at org.eclipse.jetty.websocket.common.extensions.AbstractExtension.nextIncomingFrame(AbstractExtension.java:163)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.nextIncomingFrame(PerMessageDeflateExtension.java:92)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.incomingFrame(PerMessageDeflateExtension.java:66)
        at org.eclipse.jetty.websocket.common.extensions.ExtensionStack.incomingFrame(ExtensionStack.java:210)
        at org.eclipse.jetty.websocket.common.Parser.notifyFrame(Parser.java:219)
        at org.eclipse.jetty.websocket.common.Parser.parse(Parser.java:257)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.read(AbstractWebSocketConnection.java:500)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.onFillable(AbstractWebSocketConnection.java:409)
        at org.eclipse.jetty.io.AbstractConnection$1.run(AbstractConnection.java:505)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
        at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
        at java.lang.Thread.run(Thread.java:744)
Caused by:
java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
        at java.util.ArrayList$Itr.next(ArrayList.java:831)
        at TestServer.broadcast(TestServer.java:61)
        at TestServer.removeClient(TestServer.java:45)
        at ClientSocket.onClose(ClientSocket.java:22)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.eclipse.jetty.websocket.common.events.annotated.CallableMethod.call(CallableMethod.java:71)
        at org.eclipse.jetty.websocket.common.events.annotated.OptionalSessionCallableMethod.call(OptionalSessionCallableMethod.java:68)
        at org.eclipse.jetty.websocket.common.events.JettyAnnotatedEventDriver.onClose(JettyAnnotatedEventDriver.java:122)
        at org.eclipse.jetty.websocket.common.events.AbstractEventDriver.incomingFrame(AbstractEventDriver.java:125)
        at org.eclipse.jetty.websocket.common.WebSocketSession.incomingFrame(WebSocketSession.java:302)
        at org.eclipse.jetty.websocket.common.extensions.AbstractExtension.nextIncomingFrame(AbstractExtension.java:163)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.nextIncomingFrame(PerMessageDeflateExtension.java:92)
        at org.eclipse.jetty.websocket.common.extensions.compress.PerMessageDeflateExtension.incomingFrame(PerMessageDeflateExtension.java:66)
        at org.eclipse.jetty.websocket.common.extensions.ExtensionStack.incomingFrame(ExtensionStack.java:210)
        at org.eclipse.jetty.websocket.common.Parser.notifyFrame(Parser.java:219)
        at org.eclipse.jetty.websocket.common.Parser.parse(Parser.java:257)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.read(AbstractWebSocketConnection.java:500)
        at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.onFillable(AbstractWebSocketConnection.java:409)
        at org.eclipse.jetty.io.AbstractConnection$1.run(AbstractConnection.java:505)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
        at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
        at java.lang.Thread.run(Thread.java:744)
[2014-04-17 17:40:17.97] testclient7(94.246.80.30) error: Cannot call method public void ClientSocket#onClose(org.eclipse.jetty.websocket.api.Session, int, java.lang.String) with args: [org.eclipse.jetty.websocket.common.WebSocketSession, java.lang.Integer, <null>]

當同時斷開所有客戶端時，有時會出現多個客戶端這種情況。 我很確定這與ClientSocket對象在廣播同時消失有關。

1 個解決方案

解決方案1
 1 已采納  2014-07-02 14:17:47

更換： 

private ArrayList<ClientSocket> clients = new ArrayList<>();

附： 

private List<ClientSocket> clients = new CopyOnWriteArrayList<>();

在您的廣播方法中，只需對每個語句使用： 

for( ClientSocket client : clients )
{
  if ( !client.equals(excludedClient) && client.session.isOpen() )
  {
    // Broadcast...
  }
}

這將為您提供線程安全的迭代。 發生ConcurrentModificationException是因為您在迭代列表的同時修改了List。 CopyOnWriteArrayList在寫入時復制內部數組，因此修改不會干擾迭代。 當然，這增加了更改列表的開銷，因此您可能需要考慮另一種確保線程安全的方法，但是我懷疑這足以滿足您的需求。 如果讀取比寫入更常見（通常是這種情況），那么“寫入時復制”數據結構會很好。

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