Socket Programming Multiple Client To One Server

Here for this program we are giving the same name in command prompt for both server & client. The quickest way to do this is to right click on each project and select ‘ Open Folder In Windows Explorer ‘. Use sendto() for sending data. listen(5) # Now wait for client connection. In this article, we will see how to create a C# socket and setup a listener server node that starts listening to any messages coming its way via the predefined IP and protocol. Multiple clients communicating to one socket Is it possible to have multiple client "c" programs communicating to the same server using the same socket. It is possible to have multiple TWS instances running on the same computer if each is configured with a different API socket port number. Each client computer must use an operating system that allows it to be identified to participate in the network. slice() function. IO allows you to "namespace" your sockets, which essentially means assigning different endpoints or paths. Every server is a program that runs on a specific system and listens on a specific port. The initial socket is thereby free for other clients that might want to connect with the server. That so, each time the server receives a new incoming client connection, spawn a new thread that will process that particular connection. If the TCP socket timeout option is enabled for an Informix database connection, any Informix client thread blocked for receiving the expected server response gets timed by the operating system when the timeout period expires. My questions follow the programs. Take a minute and think through the ramifications if B were the case. You're gonna need multiple threads to handle multiple connections. Execute the file with [cc inline=”1″]java TCPClient – leave off the. The client is built with an asynchronous socket, so execution of the client application is not suspended while the server returns a response. C# Multi threaded socket programming C# Multithreaded Socket Programming describes that a Multithreaded Socket Server can communicate with more than one client at the same time in the same network. One for reading from the socket and other for writing to socket. The quickest way to do this is to right click on each project and select ‘ Open Folder In Windows Explorer ‘. X11 connections, arbitrary TCP ports and UNIX-domain sockets can also be forwarded over the secure channel. The following example program creates a client that connects to a server. So, if you put all three together, Socket may be viewed as a link that is hooked to the Port of the IP address of the hosts where TCP or UDP define the rules of the game. A socket is defined as "the endpoint in a connection. Comet (programming) Jump to navigation Jump to search. NET MultiThreaded Server Socket Programming MultiThreaded Server Socket Program here is a VB. Make Use of Java Socket Programming 2. File transfer through socket in Java. If you want to measure the bi-directional bandwidth simultaneously, use the -d keyword. This is my first network programming codes writing for a client who has the following requirement: My Server has to run 24*7*365 for multiple clients at the same time (concurrency). So lets take a look at a simple python server first. geeksforgeeks. Tech support scams are an industry-wide issue where scammers trick you into paying for unnecessary technical support services. Typically the server will have multiple connected children of the original socket s, and, for each one, a process attached to it. Once a connection is established, two threads are creating. Learn to build a simple socket client, a socket server that handles one connection at a time, and a socket server that can handle mulitple socket connections. clients = clients; this. /client SERVER CLIENT. Hi, I have one server that creates thread for each client with tcp connection ,and in the client side each client creates thread to send multiple objects. There is some flexibility with this number; you can vary it. You can specify the sender and multiple recipients including CC and BCC. This program can then be made setuid root. Specially if your client is collecting data, or interacting with multiple APIs or services. TCP Ports, Connections and Connection Identification (Page 2 of 2) Multiple Connection Management. Afterwards it will distribute and forward the data to the correct server(s). Socket class represents the socket between the client and the server, and the java. Our first implementation of the Web server will be multi-threaded, where the processing of each incoming request will take place inside a separate thread of execution. So our Student. TCP Client/Server Example¶ Introduction¶ We will now use the elementary functions from the previous chapter to write a complete TCP client/server example. I've managed to make one client recieve output of ls -l command, sometimes, its buggy. A server socket must call the Bind() method to indicate which interface the server will listen on. I am using on the server side an array of int's declared at the beginning of the application, that will contain the socket descriptor returned by the "accept. I'm assuming you mean "how can I have multiple client socket connections to my server process implemented in Java?" A web server is a good example of this scenario. Redirection messages 300 Multiple Choice The request has more than one possible response. We will also learn how server client program read and write data on socket. It'll cause the library to spew out the entire. The reason is a port can be used by a single process, which allocates the port (doing "bind" as a server that will listen to that. Once the server disconnects the connection, the client exists itself. Our simple example is an echo server that performs the following steps: The client reads a line of text from its standard input and writes the line to the server. Method accept() returns when a client has connected to your server. – viraptor Aug 2 '11 at 12:45. Once the connection is accepted by the server, each program can communicate via input-output channels over the sockets created at both ends. Pyhon Socket programming Socket programming is one of the most fundamental technologies of computer network programming. The main HTTP tunnel connection is disconnected if either the server or client closes the network connection. Example of client/server with select(). Python network sockets programming tutorial In this tutorial you will learn about in network programming. Once a connection is established, two threads are creating. I'm having trouble introduce multi‐threading in SimpleServer. You can help protect yourself from scammers by verifying that the contact is a Microsoft Agent or Microsoft Employee and that the phone number is an official Microsoft global customer service number. Several thread limits are discussed in more detail later in this tutorial. Document collaboration Allow users to concurrently edit a document and see each other's changes. but the issue is that it comunicates with both servers but when i send message from server to this client it replies to first server only one time and and to 2nd server multiple times. So you create a DatagramSocket. SslStream etc to connect to a IMAP server like Gmail and send commands to the server and downloading one's email from one's account , programatically. Multiple clients communicating to one socket Is it possible to have multiple client "c" programs communicating to the same server using the same socket. In this post we shall learn how to write a simple socket server in python. The server socket is 8080 so to get more than one person talking to the server at once, the server needs to hand off socket connections to a different port. We will be configuring two domain names that will resolve. The multiple client server is all messed up and doesn’t even work properly, trash and useless. FTP must create a new one for each new data transfer. now my client able to connect to one server only. Create the server, bind, listen. System Center Components. Alternatively, a server can handle multiple clients at the same time in parallel, and this type of a server is called a concurrent server. It can handle the varying load of your application traffic in a single Availability Zone or across multiple Availability Zones. The first step is for the API client to initiate a connection to TWS on a socket port where TWS is already listening. Then lets say a client A tries to connect to the server (make TCP/IP connection). After both ends of a TCP/IP socket are connected, communication is bi-directional. js and socket. 03/30/2017; 5 minutes to read +7; In this article. If one remote machine makes multiple connections, each one will use a different remote port. What happens in the web server is a bit more complex. The syntax might vary, but the underlying concept is the same. OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. This document covers information on setting up SSL virtualhosts, creating keyfiles, certificates along with how to protect access to directories and URLs to specific ciphers. It appears you can get this behavior by selecting zero for the port number, for example, my test below printed "127. There are several configuration options and optimization techniques which can significantly improve the performance of HttpClient. Gettys Category: Standards Track Compaq/W3C J. So you create a DatagramSocket. All clients are running smoothly. The maximum number of threads allowed is determined by the final int maxthreads. * snippet of a threaded Python server. Socket programming is used for developing client-server applications in Java. You will learn about the client-server model that is in use for the World Wide Web, E-mail and many other applications. Each client connects, pushes data, disconnects, waits 5 seconds, then continues the cycle. A common variation of this setup is a LAMP stack, which stands for Linux, Apache, MySQL, and PHP, on a single server. The user-agent or user should choose one of them. >> I'm getting a much better of socket programming each time I rewrite the server program That's actually my credo in a nutshell: Write it, run it, delete it, write it, run it, delete it, ad infinitum. ) Outline of a TCP. Client (Client. I am successful in one-one communication that is one client - one server Networking in C# - one Server to multiple clients. For the program example that demonstrates the use of the send() functions on server and client please refer to the previous chapter. It could then copy the data sent from the client to the telnet socket, and vice-versa. Hello, I am developing a software in Visual Studio 2013 C#. Each line of the code are explained through comments. For write, I use it once in server, and once in client - on both places I shall compare if number of bytes written is equal to the number of bytes I requested to write, and if not - abort program or smth, that is your suggestion right? \$\endgroup\$ – user38434 Mar 10 '14 at 11:33. 0 the cluster module doesn’t work. bind((host, port)) # Bind to the port s. This is my first network programming codes writing for a client who has the following requirement: My Server has to run 24*7*365 for multiple clients at the same time (concurrency). url The base url of the application under test. Client programs send requests to the server program, and the server program responds to the request. Another problem is. HttpClient can also be instructed to retry the method even though the request may have already been processed by the server and the I/O exception has occurred while receiving the response. This client/server pair runs a simple TCP socket program as an Echo Server that only allows one client to connect to the server. Socket Programming - Multi-Client Server chat application using java swing & Android - aboullaite/Multi-Client-Server-chat-application. Two sockets are defined in MainPage. Apache Thrift allows you to define data types and service interfaces in a simple definition file. Must be a positive integer. For write, I use it once in server, and once in client - on both places I shall compare if number of bytes written is equal to the number of bytes I requested to write, and if not - abort program or smth, that is your suggestion right? \$\endgroup\$ – user38434 Mar 10 '14 at 11:33. print 'Server listening' while True: conn, addr = s. I've done my research but i still can't making things work. i dont get. You exploit this behavior to simplify the development of the server. Next: Socket Programming in C/C++: Handling multiple clients on server without multi threading This article is contributed by Akshat Sinha. First when client send request to server means that when you load a web page, your computer sends TCP (bytes forms)packets to the web server’s address, then server send the web page to you as response. From one DOS prompt, first, run the server program and from the other DOS prompt run the client program. According to Daniel Roth, principal program manager for ASP. To compile these, install Java JDK to your system. /client SERVER CLIENT. Let experiment the examples in this lesson in different ways: run multiple clients, test on local computer, and test on different computers (the server runs on a machine and the client runs on another). The socket is called serverSocket. /dev/ttyUSB0 is reachable at :7000. Our simple example is an echo server that performs the following steps: The client reads a line of text from its standard input and writes the line to the server. 20) The UDP server described in Section 2. For a server socket on the Internet, an address consists of a port number on the host machine. The code is based on the singlethreaded server desbribed in the text on Singlethreaded Servers. All one can think and do in a short time is to think what one already knows and to do as one has always done! Java Multithreaded Socket server example code In this example we have created a server that listens on port 11111 and accepts any number of incoming request from a client. Client-server. It uses TcpClient and UdpClient classes instead of the traditional way employed in v1. You can also use a TCP connection to stream large amounts of data in real-time, but this can be a problem when you might need more than one client (receiver of the data from the Particle), or the client moves from machine to machine or the destination IP address changes frequently. Essentially, sftp is a drop-in replacement for the standard command-line ftp client, but with ssh authentication. I am successful in one-one communication that is one client - one server Networking in C# - one Server to multiple clients. It boasts a clean interface and an easy-to-use interface. Your client will connect to the server using a TCP connection, send an HTTP request to the server, and display the server response as an output. Safeguard sensitive data, achieve compliance requirements and provide secure file sharing tools. The maximum number of threads allowed is determined by the final int maxthreads. It is written in java and supports many advanced chat functionality including secure connections, emoticons, administrative class users, and more. Explanation: The client in socket programming must know IP address of Server. Sockets are one of the most popular means of network communication. This sample program, based on the one in the standard library documentation, receives. Another approach might be to make a program on the robot using the Client-Server approach via a TCP socket – and the transfer data into the running program on the robot – thereby the data is inside the Polyscope environment. I am trying to create an application that uses TCP sockets under Unix, where multiple clients connect to one server. A Quick Example. The server can handle at most one connection at a time. Each message sent by one client is forwarded to all other clients. If you have built MySQLdb with embedded server support, there are two additional functions you will need to make use of: server_init(args, groups) Initialize embedded server. The prototype is as the following:. Send File from Server to Client using C# Socket Programming Hello Friends, after long day's gap I am writing some blog for you. In this post we are going to write a very simple chat application in python that is powered by sockets. In the socket programming model, a socket represents an endpoint of a communication channel. socket program multi client chat server by gui, Search on socket program multi client chat server by gui. 896 CHAPTER 12. For example, domain name servers (see 8. Execute the file with [cc inline=”1″]java TCPClient – leave off the. This application will show you the simplest way to transfer messages through Sockets between many connected users on the same network. Our first implementation of the Web server will be multi-threaded, where the processing of each incoming request will take place inside a separate thread of execution. Then the server accepts the connection from the client. java and ServerMain. Finally, if you have already set your account in your email client such as Outlook or Window Mail, you can query your SMTP server address, user in your email client. Another option, the one I investigate here, is to use multicast. I would like the server to take create a master socket and then listen on this socket until a incoming connection comes in. We will watch the server window and understand the flow. More specifically, we’ll look at the socket API for Internet sockets, sometimes called Berkeley or BSD sockets. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. cs: Similar to te changes made to the server program, this client program employs a more efficient way of socket programming provided by the. A socket is an endpoint of a two-way communication link between two programs running on the network. There is no such interdependence in the sockets and CAsyncSocket, even within one thread. Note that multicast and a network broadcast are different and that multicast is a UDP broadcast only. The number of automatic retries can be increased. 2 CLIENT / SERVER MODEL The MODBUS messaging service provides a Client/Server communication between devices connected on an Ethernet TCP/IP network. The function tcpconnectshows all the steps necessary to connect to a TCP server. "accessed from a thread other than the thread it was created on". Sockets for managed implementation of Internet protocols that. Now you have a very basic working Web server that you can test with your browser or some other HTTP client. To keep the server example simple, you designed it to listen for and handle a single connection request. Multiple clients communicating to one socket Is it possible to have multiple client "c" programs communicating to the same server using the same socket. Example: Connecting a TCP server to a client, a server program. The client socket then can notify when the data is available. If you want to run multiple Emacs daemons (see Initial Options), you can give each daemon its own server name like this: emacs --daemon=foo. java on a machine which. -b windowsize Size of TCP send/receive buffer, in bytes. Therefore, one solution to this problem is to have an asynchronous task to manage our server-client communication. In this tutorial we shall. Let us write a very simple client program which opens a connection to a given port 12345 and a given host. But I have not tried to use Features this way before. Recently, I wrote code that touched at least 3 different services/APIs. Multi-threaded chat Application in Java | Set 1 (Server Side Programming) Prerequisites : Introducing threads in socket programming In the above article, a simple date time server was created which handled multiple user requests at the same time using threading. This does not handle multiple clients well; each client must wait until the previous client is completely served before it even gets accepted. Accessing Files Using SFTP on Linux Secure File Transfer Protocol (sftp) is a file transfer program which runs over an ssh tunnel and uses many features of ssh, including compression and encryption. The server is built with an asynchronous socket, so execution of the server application is not suspended while it waits for a connection from a client. The remote machine is the other one, the one that is the argument of the ftp command. HttpClient can also be instructed to retry the method even though the request may have already been processed by the server and the I/O exception has occurred while receiving the response. Therefore, one solution to this problem is to have an asynchronous task to manage our server-client communication. A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server should connect to the client's data port to initiate a data transfer. Simple IMAP CLIENT This is article is about using System. One idea is that you have the server listen on that 1 port. • An implementation guideline that proposes the object model of an MODBUS implementation example. What we have to do to give the same program name for the sockets in the program itself (can we use #define and assign a name for program). This is the type of application that I'll be covering in this tutorial. You can use the mail server settings in this article to manually set up your email app to send and receive email with an iCloud email account. Here the client program is connected to Server's PORT 8888, and IP Address here we give Server Address as "127. c# documentation: Asynchronous Socket (Client / Server) example. So multiple clients can communicate with the server with each client corresponds to a particular thread of the server. Learn to build a simple socket client, a socket server that handles one connection at a time, and a socket server that can handle mulitple socket connections. The URL Connection class can be used to read and write data to the specified resource referred by the URL. c it shows ip address of. If the client user types ". I have control of the server code but not the clients, because they are specialized gps devices. If the client program running on other machine, then you can give the IP Address of that. The Client program remains unchanged. 1 you can do it by including an option "domain-name-servers" to DHCP's configuration file. The client initiates the TCP connection by using sockets on port 80 to the server. Multi-threaded chat Application in Java | Set 1 (Server Side Programming) Prerequisites : Introducing threads in socket programming In the above article, a simple date time server was created which handled multiple user requests at the same time using threading. This document covers information on setting up SSL virtualhosts, creating keyfiles, certificates along with how to protect access to directories and URLs to specific ciphers. Our application has a client and a server. If so, how does the server know which client to send a message back to. No matter which socket programming interface you select, function is identical. First up is Evan Huack, who digs into cudafy, a library on codeplex that allows you to run C# code (any IL code actually) on your GPU. Skip to content. 0) protocol, a security protocol that provides communications privacy over the Internet. A Quick Example of Client/Server Interaction with UDP. - It needs a new socket (consequently a different port number) so that it can continue to listen to the original socket for connection requests while serving the connected client. 1 devices are capable of connecting to the Internet and other devices in myriad ways. net) takes care of all of. Programming sockets in Java. Use socket() with AF_INET and SOCK_DGRAM arguments as normal. A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server should connect to the client's data port to initiate a data transfer. js application should include the socket. ) Byte Ordering 5. C# Multi threaded Client Socket programming C# Multithreaded Client Socket Program here is a C# Windows based application and it can connect to the Server and send the message to the Server. Our goal is simply to bring you the best FTP software on the internet. Concurrent Servers − This type of server runs multiple concurrent processes to serve many requests at a time because one process may take longer and another client cannot wait for so long. java) sends back the result (message) to the client (Client. Then lets say a client A tries to connect to the server (make TCP/IP connection). One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows. Some good examples of client-server pairs are telnet/telnetd, ftp/ftpd, or Firefox/Apache. For a typical web application, that would include the web server, application server, and database server. They are treated as different sockets by the operating system, since the remote socket address (the client IP address and/or port number) are. Before diving deeper into this. The first example is a conventional client -server in which the client as well as the server are applications. For example, when you open up your browser, you as a client are creating a connection to the server for the transfer of information. They go like this: Server: "Knock Knock!". Each thread has a limited lifetime, and when it goes away, that leaves space for the creation of a new thread. Let’s implement simple TCP/IP client-server application which allows to exchange with string messages. Connecting to the socket server with a client. The server echos all input it receives from the client back through the socket to the client. If you have an email client on your computer, the software is connecting to an IMAP or POP server to download your messages to your computer, and an SMTP server to send messages back through the email server. A user interface for the standard File Transfer Protocol for ARPANET, FTP acts as an interpreter on the remote. Tech support scams are an industry-wide issue where scammers trick you into paying for unnecessary technical support services. Cross Language Clients. You exploit this behavior to simplify the development of the server. When started this server runs with a single thread and listens for an incoming connection. In this snippet I will try to show you a simple connection between an Android client device and a Java server app over a local network. Writing the Server Side of a Socket The section shows you how to write the server side of a socket connection through a complete client/server example. [Tile server and a client neatly] I will click "Connect" button on one of the clients. A server listens for connection requests from clients across the network or even from the same machine. You need not know anything about Perl or socket programming in Perl, nonetheless you might want to refer it if you wish to. During this time many things has changed in technological world like earlier I write code with VS 2008 and now VS 2012 has released. class, or you will get the error: “Exception in thread “main” java. The library is single threaded, but it is not limited to one thread. net asp asp. 12: You may call bind() after the call to socket(), if you wish to specify which port and interface that should be used for the client socket. Socket Examples Prof. py import socket # Import socket module port = 60000 # Reserve a port for your service. Essentially, sftp is a drop-in replacement for the standard command-line ftp client, but with ssh authentication. Client file contain only one public class Client (for creating a client). I am using on the server side an array of int's declared at the beginning of the application, that will contain the socket descriptor returned by the "accept. Sockets is a method for communication between a client program and a server program in a network. To keep the server example simple, you designed it to listen for and handle a single connection request. Chat Program Java is a continuous communication between two systems. when there is a client(the other code I make) connects to it, the select() succeeds and accept() works. Secure Sockets Layer (SSL) is a standard security technology for establishing an encrypted link between a server and a client—typically a web server (website) and a browser, or a mail server and a mail client (e. psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket "/tmp/. NoClassDefFoundError”. Screen and tmux's behaviour for when multiple clients are attached to one session differs slightly. It is also a general-purpose cryptography library. For write, I use it once in server, and once in client - on both places I shall compare if number of bytes written is equal to the number of bytes I requested to write, and if not - abort program or smth, that is your suggestion right? \$\endgroup\$ – user38434 Mar 10 '14 at 11:33. Clients know how to connect to the server via an IP address and port number. Typically the server will have multiple connected children of the original socket s, and, for each one, a process attached to it. Figure 214: TCP Connection Termination Procedure This diagram shows the conventional termination procedure for a TCP session, with one device initiating termination and the other responding. Example: Connecting a TCP server to a client, a server program. I have control of the server code but not the clients, because they are specialized gps devices. print 'Server listening' while True: conn, addr = s. You should fix these in the server. NET at Microsoft: With Blazor a developer can write client-side web UI using. We've used socket programming concepts to implement this basic application. Since there may be number of android devices (client1) connecting to the server, 2. Sockets are not connected when they are first created, and are useless until a call to either connect (client application) or accept (server application) completes successfully. Accept method, then within a Task I pass the accepted socket to an Action that in another module manages the send recieve logic, so I have 1 new long running task per accepted socket. DataInputStream is deprecated You need to read the API doc for the DataInputStream class's readLine method. The socket. In order to be notified of incoming connections on a socket, you can use select(2) or poll(2). general, a client wishing to create a TCP connection to a server first calls socket to create a socket, optionally calls bind to specify a local address, and finally connects to the server using the connect system call. A general-purpose edge node would be well served by a processor configuration similar to one used for slave nodes — specifically, a dual-socket server with Ivy Bridge processors clocked at between 2 and 2. *; import javax. Calls used in this example are, bind, close, connect, accept, send, recv. Multiple Sockets Now lets say you have two sockets connecting to either two different servers or same server (which is perfectly valid). Here server listens for incoming requests and once connection is established, it simply replies Smile from the server. NET with code samples, project and program examples presented with screenshots and sample outputs. The client in socket programming must know two information: IP Address of Server, and; Port number. Thats it, if the socket server is running, you should be able to see the data streaming in the msys. write send information to the server and the server response it, the problem I was having is: the event server. From a server's perspective, at any point in time, it is not unusual for a server to be communicating with multiple clients. os = new PrintWriter. For myself this is primarily being a contractor I have a corporate virtual desktop with email etc, then I'm working on mutiple customers VMware View environments in the datacenter implementing and testing. Normally, server sockets may accept multiple client connections. If it is important that Client A and Client B read the same value, Client B should should call the sync() method from the ZooKeeper API method before it performs its read. To connect to an SSL HTTP server the command: openssl s_client -connect servername:443 would typically be used (https uses port 443). This tutorial walks through how you can send data from device-to-device, client-to-server, and vice versa using socket programming in Python. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows. In computing, a web application or web app is a client–server computer program that the client (including the user interface and client-side logic) runs in a web browser. iOS Framework Allowing you to connect to Redis server with Swift programming language. Typically, the local port and local IP will be the same for all connections to a server process (e. Where TCP is a stream oriented protocol, ensuring that all of the data is transmitted in the right order, UDP is a message oriented protocol. In this example the client send a number to the server and in response to each client, the server send back the square of the received number. In the POSIX-series operating system, the socket is a kind of a file. 1" , because Server and Client program run on the same machine. This is a very simple Client/Server Chat Application using TCP Sockets Java. Here is my new code, I actually took it from a previous forum question similar to mine, I basically just copied the method "readFromSocket" as a lamda expression to put into the thread as the new method. This is an fine example for Scoket Programmin in java. This tutorial demonstrates steps on how-to construct or build the client server socket/winsock/windows socket communication using the C#. A flexible & easy-to-manage web server Internet Information Services (IIS) for Windows® Server is a flexible, secure and manageable Web server for hosting anything on the Web. Multithreaded Socket Programming describes that a Multithreaded Socket Server can communicate with more than one client at the same time in the same network. Since there are no extra jumps to servers and translation etc the code executes very fast. Note: In this tutorial we will show how to program sockets in Java using the TCP/IP protocol only since it is more widely used than UDP/IP. recvfrom(2) - Linux man page Name. NET and C# instead of JavaScript. NET MultiThreaded Socket Programming Multithreaded Socket Programming means that a Multithreaded Server can communicate with more than one clients at the same time. ) Outline of a TCP Server 7. I'm having trouble introduce multi‐threading in SimpleServer.