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CryoGenesis

(SOLVED) Multi-threading help!

3 posts in this topic

SOLVED: (Just in case anyone else has any trouble with something like this) The problem was that when you initialize a separate thread and pass objects from another thread into the new thread, it creates a copy of said object instead of referencing it like Java is supposed to do. To solve this you use the 'protected' keyword in front of the objects that you don't want to be copied.

 

Hey, I'm working on a multi-threaded server program which isn't working how I would like.
Basically, there is a thread that runs a program (main thread), a thread which accepts any connections and a thread for each connection which checks if the client is still connected.
-ServerProgram
-ConnectionGrabber
-Connection
Unfortunately, when the ConnectionGrabber thread accepts a connection, it initialized a Connection class with the socket. the Connection class then starts a thread and accesses the socket through the run() method (it implements Runnable).
For some reason, when the client is passed from the ConnectionGrabber thread to the Connection thread, the client is not the same object. When you send information to the client through the connectionGrabber thread it sends successfully, when you send it through the connection thread, it sends without an error but does not actually send it to the client. client.isClosed() also doesn't work when passing the object between threads.

here is the full code:

package Networking;import static Util.ConsoleUtil.*;import java.io.BufferedWriter;import java.io.DataOutputStream;import java.net.*;import java.util.*;public class ServerProgram {	ArrayList socketList;	Server server;	public void begin(Server server){		this.server = server;		socketList = new ArrayList();		consoleOutput("BEGINNING SERVER PROGRAM");		boolean running = true;				consoleOutput("Loading any Connections");		while(running == true){			update();					}	}	public void update(){		checkList();	}	public void checkList(){		for(int i = 0; i < Connection.connectionList.size(); i++){			Connection client = Connection.connectionList.get(i);			if(client.disconnected() == true){				Connection.connectionList.remove(client);				Connection.connectionList.trimToSize();				consoleOutput("Successfully Dropped A Client");			}		}	}	public static void sendMessage(Socket socket, String message) throws Exception{		new DataOutputStream(socket.getOutputStream()).writeBytes(message);	}}
package Networking;import static Util.ConsoleUtil.consoleOutput;import java.io.IOException;import java.net.ServerSocket;import java.net.Socket;import java.util.ArrayList;import Util.ConsoleUtil;public class ConnectionGrabber implements Runnable{	ServerSocket server;	boolean accepting = true;	Thread thread;		public ConnectionGrabber(ServerSocket server){		this.server = server;		thread = new Thread(this);		consoleOutput("Initialized Connection Grabber");	}		public void startAccepting(){		accepting = true;		if(thread.isAlive() == false){			thread.start();		}	}	public void stopAccepting(){		accepting = false;	}	public void run() {		consoleOutput("Now Accepting Incoming Connections");		while(accepting == true){			try {				Socket sock = server.accept();				Connection connection = new Connection(sock);				Connection.connectionList.add(connection);				consoleOutput("Connection Added To Connection List... Current Amount Of Connections: " + Connection.connectionList.size());			} catch (Exception e) {				e.printStackTrace();			}		}	}}
package Networking;import java.io.*;import java.net.Socket;import java.util.ArrayList;import static Util.ConsoleUtil.*;public class Connection implements Runnable{	public static ArrayList connectionList = new ArrayList();		final Socket client;	boolean checking = true;	Thread thread;		public Connection(Socket socket){		client = socket;		thread = new Thread(this);		thread.start();	}		public synchronized boolean disconnected(){		return !checking;	}		public synchronized void stopConnection(){		checking = false;	}		public void run() {			BufferedInputStream in = null;		PrintWriter out = null;		try{			in = new BufferedInputStream(new DataInputStream(client.getInputStream()));			out = new PrintWriter(client.getOutputStream());		}catch(Exception e){			consoleOutput("Failure To Establish Data Stream To Client... Dropping client...");			checking = false;		}		consoleOutput("Established Data Transfer");		while(checking == true){						try{				out.print(1000);			}catch(Exception e){				consoleOutput("Transfer Check Failed");				checking = false;			}						if(client.isClosed() == true || client.isConnected() == false){				checking = false;				consoleOutput("Client Dropped");			}						try{				thread.sleep(1000);			}catch(Exception e){							}		}	}	}

(ConnectionGrabber is initialized in another class)

Thanks in advance!
Any help at all will be appreciated!

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Hmm. The code looks quite good. But you have to print the exceptions you are not handling otherwise. How else can you find bugs in your code? "Plain" Java has e.printStackTrace(), with log4j (Java logging library), you can do something like log.error("Exception there and there",e). 

 

Please add e.printStackTrace() to all exception handlers, a line that sends data from ConnectionGrabber to the client and provide logs from both applications. That way, I can debug it.

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Hmm. The code looks quite good. But you have to print the exceptions you are not handling otherwise. How else can you find bugs in your code? "Plain" Java has e.printStackTrace(), with log4j (Java logging library), you can do something like log.error("Exception there and there",e). 

 

Please add e.printStackTrace() to all exception handlers, a line that sends data from ConnectionGrabber to the client and provide logs from both applications. That way, I can debug it.

 

It doesn't actually produce any errors. When I send data to the client from ConnectionGrabber to the client (right after server.accept()) it receives information on the client side. When I pass the client to the Connection class it does something weird and no data is received on the client side(a separate program running on my laptop).

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