# Troubleshooting Data Handling Issues in a Multithreaded Server Class for Multiple Client Connections

**URL:** <https://discourse.processing.org/t/troubleshooting-data-handling-issues-in-a-multithreaded-server-class-for-multiple-client-connections/44653>\
**Category:** Coding Questions\
**Created:** [June 26, 2024, 4:22pm UTC](https://discourse.processing.org/t/troubleshooting-data-handling-issues-in-a-multithreaded-server-class-for-multiple-client-connections/44653 "2024-06-26T16:22:42Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![hakim](https://avatars.discourse-cdn.com/v4/letter/h/97f17d/32.png) [@hakim](https://discourse.processing.org/u/hakim)\
**Post date:** [June 26, 2024, 4:22pm UTC](https://discourse.processing.org/t/troubleshooting-data-handling-issues-in-a-multithreaded-server-class-for-multiple-client-connections/44653/1 "2024-06-26T16:22:42Z")

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Hello, I hope you’re doing well. I did a server class to handle multiple client connections simultaneously. Each client sends a fixed amount of data that I want to store and then process into a CSV file. Here is the complete code for the server class:

```auto
import java.io.*;
import java.net.*;
import java.util.concurrent.*;

class ServerHandler implements Runnable {
    private ServerSocket server;
    private boolean serverRunning = true;
    private String receivedMessage = null;
    private int port;
    private boolean isConfigserver;
     private ExecutorService clientThreadPool;
    
      public ServerHandler(int port, boolean isConfigserver) {
        this.port = port;
        this.isConfigserver=isConfigserver;
        this.clientThreadPool = Executors.newFixedThreadPool(10);
    }
    @Override
    public void run() {
        try {
            // Create a server socket to listen on port 1234
            server = new ServerSocket(this.port);
            println("Server is running on port : ");
            print(this.port);
            
            while (serverRunning) {
                try {     
                      Socket client = server.accept(); // Accept incoming connections
                    System.out.println("Client connected: " + client.getInetAddress());
                    if(!isConfigserver) {
                             // Handle each client connection in a separate thread
                    ClientHandler clientHandler = new ClientHandler(client, selectedMode, Nombre_mesures);
                    clientThreadPool.submit(clientHandler);
                    }
                    else {
                       BufferedReader reader = new BufferedReader(new InputStreamReader(client.getInputStream()));
                       String receivedData = reader.readLine();
                              if (receivedData != null) {
                                  receivedData = receivedData.trim();
                                  println("Received from Arduino about config: " + receivedData);
                                  if(receivedData.equals("OK")) {
                                    isReady=true;
                                    println("we are ready to go");
                                  }
                              }
                              client.close();
                               println("Client connection closed after configuration");
                    }
                 
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } 
    }
    public void stopServer() {
    serverRunning = false;
    if (server != null && !server.isClosed()) {
        try {
            server.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
     clientThreadPool.shutdown();
}
private class ClientHandler implements Runnable {
        private Socket client;
        private String selectedMode;
        private int Nombre_mesures;
        private int counter_requete = 0;

        public ClientHandler(Socket client, String selectedMode, int Nombre_mesures) {
            this.client = client;
            this.selectedMode = selectedMode;
            this.Nombre_mesures = Nombre_mesures;
        }

        @Override
        public void run() {
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(client.getInputStream()))) {
  
                    while (counter_requete < Nombre_mesures) {
                        String receivedData = reader.readLine();
                        if (receivedData != null) {
                            receivedData = receivedData.trim();
                            System.out.println("Received from Arduino: " + receivedData);
                            extractAndWriteData(receivedData, selectedMode,counter_requete);
                            counter_requete++;
                            println("voici le counter en cours : " + counter_requete);
                        }
                    }
                       counter_requete = 0;
                 
    
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    client.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                System.out.println("Client connection closed");
            }
        }

}
}

```

I implemented multithreading to manage multiple connections simultaneously. However, I’m currently facing an issue within the client class, specifically in the `extractData` function where the data processing occurs. The code for this function is as follows:

```auto
void extractAndWriteData(String msg, String selectedMode, int compteur) {
  // Split the message by commas to extract individual parts
  String[] parts = msg.split(",");
   String identifiant_GW=parts[0];
       switch (selectedMode) {
        case "Mode 1":
         
            break;
        case "Mode 2":
            // Code for Mode 2
           snrPart = parts[1];
           rssiPart = parts[2];
           timePart=parts[3];
          
          
           timePart= trim(timePart); // Trim whitespace
           temps =float(timePart)/1000;
           
           
           println(identifiant_GW,rssiPart,snrPart,timePart);
        
            try {
     int index_excel=Integer.parseInt(identifiant_GW);
    int index = gatewayList.indexOf(index_excel);
    if (index == -1) {
        println("Invalid index_excel: " + index_excel);
        return;
    }
    if (outputWriters[index] == null) {
        println("Output writer not initialized for index: " + index);
        return;
    }

    // Log before writing to the file
    println("Writing to file for index: " + index);
    outputWriters[index].println(identifiant_GW + ";" + rssiPart + ";" + snrPart + ";" + timePart + ";" + x_position + ";" + y_position + ";" + z_position);
    println("Successfully wrote to file for index: " + index);
} catch (Exception e) {
    println("Exception while writing to file: " + e.getMessage());
    e.printStackTrace();
}
           
  
          

break
        default:
            // Default code if SelectedMode does not match any case
            break;
    }
      
      if (compteur >= Nombre_mesures) {
         outputWriters[gatewayList.indexOf(Integer.parseInt(identifiant_GW))].flush();
         outputWriters[gatewayList.indexOf(Integer.parseInt(identifiant_GW))].close();
        println("File closed after reaching the required number of measurements for GW : "+ identifiant_GW);
     } 
}

```

my problem is once the client reach to step were he needs to write the current measure into the csv file he disconnect directly, however if i comment that line ( the outputwriter line) , i can print all data in terminal, so i m wondering what s the issue, is it a synchronisation problem ?  
PS : the excel file are created at the very beginning of the sketch and the code was functioning well before multithreading ( when i only had one client and not multiple ones), can you suggest to me a solution ?

---

<div class="post-metadata">

**Author:** ![mnse](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/mnse/32/16520_2.png) [@mnse](https://discourse.processing.org/u/mnse)\
**Post date:** [June 28, 2024, 6:32pm UTC](https://discourse.processing.org/t/troubleshooting-data-handling-issues-in-a-multithreaded-server-class-for-multiple-client-connections/44653/2 "2024-06-28T18:32:05Z")

</div>

Hi @hakim,

Please check here.

> **[Java Concurrency | Baeldung](https://www.baeldung.com/java-concurrency)**
>
> Explore Concurrency in Java.

> **[Guide to java.util.concurrent.Locks | Baeldung](https://www.baeldung.com/java-concurrent-locks)**
>
> In this article, we explore various implementations of the Lock interface and the newly introduced in Java 9 StampedLock class.

Cheers  
— mnse