Simple socket server in C using threads (pthread library) Compiles on linux

tcp_server.c

/*
    C socket server example, handles multiple clients using threads
    Compile
    gcc server.c -lpthread -o server
*/
 
#include<stdio.h>
#include<string.h>    //strlen
#include<stdlib.h>    //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h>    //write
#include<pthread.h> //for threading , link with lpthread
 
//the thread function
void *connection_handler(void *);
 
int main(int argc , char *argv[])
{
    int socket_desc , client_sock , c;
    struct sockaddr_in server , client;
     
    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }
    puts("Socket created");
     
    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 8888 );
     
    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        //print the error message
        perror("bind failed. Error");
        return 1;
    }
    puts("bind done");
     
    //Listen
    listen(socket_desc , 3);
     
    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
     
     
    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
	pthread_t thread_id;
	
    while( (client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
        puts("Connection accepted");
         
        if( pthread_create( &thread_id , NULL ,  connection_handler , (void*) &client_sock) < 0)
        {
            perror("could not create thread");
            return 1;
        }
         
        //Now join the thread , so that we dont terminate before the thread
        //pthread_join( thread_id , NULL);
        puts("Handler assigned");
    }
     
    if (client_sock < 0)
    {
        perror("accept failed");
        return 1;
    }
     
    return 0;
}
 
/*
 * This will handle connection for each client
 * */
void *connection_handler(void *socket_desc)
{
    //Get the socket descriptor
    int sock = *(int*)socket_desc;
    int read_size;
    char *message , client_message[2000];
     
    //Send some messages to the client
    message = "Greetings! I am your connection handler\n";
    write(sock , message , strlen(message));
     
    message = "Now type something and i shall repeat what you type \n";
    write(sock , message , strlen(message));
     
    //Receive a message from client
    while( (read_size = recv(sock , client_message , 2000 , 0)) > 0 )
    {
        //end of string marker
		client_message[read_size] = '\0';
		
		//Send the message back to client
        write(sock , client_message , strlen(client_message));
		
		//clear the message buffer
		memset(client_message, 0, 2000);
    }
     
    if(read_size == 0)
    {
        puts("Client disconnected");
        fflush(stdout);
    }
    else if(read_size == -1)
    {
        perror("recv failed");
    }
         
    return 0;
} 

Better to pass the accepted socket to the thread by value rather than by reference since there might be two accept()s before connection_handler() runs. When this happens, the second accept() overwrites client_socket before connection_handler() can grab it into sock at line 88 and both threads will get the same socket descriptor. Two threads servicing the same socket is problematic.

I see that you have a commented pthread_join (//pthread_join( thread_id , NULL);) So now you are creating 'n' number of threads and not closing the. Why don't you keep an array (thread pool) to save the thread state and clear it as soon as the connection_handler job is completed?

Is it true that there is no code to check if thread has finished it's work? What if "client_sock < 0" but there still is some number of unfinished threads?

hi there! This code contains memory leak. See my reporitory for fixed version: https://github.com/mavstuff/threadtest/blob/master/server.c