前面介紹了用select函式來實現socket的非同步收發資料，但是select函式也有一些缺陷，要使socket能持續地通訊，select必須不停地檢測，這樣程序就會一直阻塞在這裡，限制了功能的擴充套件，這裡我們用多執行緒的方式，另建立兩個執行緒用來發送/接收資料，即可解決這個問題，程式碼如下：
伺服器 server.c

    #include <stdio.h>  
    #include <stdlib.h>  
    #include <string.h>  
    #include <unistd.h>  
    #include <errno.h>  
 

    #include <sys/types.h>  
    #include <sys/socket.h>  
    #include <netinet/in.h>  
    #include <arpa/inet.h>  
    #include <pthread.h>  

    void* recvsocket(void *ptr)  
    {  
        int fd = *(int *)ptr;  
        char str[1024];  

        while (1)  
        {  
            memset
 
(str, 0, sizeof(str));  
            int numbytes = recv(fd, s, sizeof(str), 0);  
            if (numbytes <= 0)  
                break;  
            printf("%s\n", str);  
        }  
        return NULL;  
    }  

    void* sendsocket(void *ptr)  
    {  
        int fd = *(int *)ptr;  
        char
 
 str[1024];  

        while (1)  
        {  
            memset(s, 0, sizeof(str));  
            read(STDIN_FILENO, str, sizeof(str));  
            send(fd, str, strlen(str), 0);  
        }  

        return NULL;  
    }  


    int main(int arg, char *args[])  
    {  




        int port = 1234;  
        int st = socket(AF_INET, SOCK_STREAM, 0); 



    int opt = SO_REUSEADDR;
    setsockopt(st, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

        struct sockaddr_in addr; 
        memset(&addr, 0, sizeof(addr));  
        addr.sin_family = AF_INET; 
        addr.sin_port = htons(port);  
        addr.sin_addr.s_addr = htonl(INADDR_ANY); 


        if (bind(st, (struct sockaddr *) &addr, sizeof(addr)) == -1)  
        {  
            printf("bind failed %s\n", strerror(errno));  
            return EXIT_FAILURE;  
        }  


        if (listen(st, 20) == -1)  
        {  
            printf("listen failed %s\n", strerror(errno));  
            return EXIT_FAILURE;  
        }  
        printf("listen success\n");  




        int client_st = 0;  
        struct sockaddr_in client_addr;

        pthread_t thrd1, thrd2;  
        while (1)  
        {  
            memset(&client_addr, 0, sizeof(client_addr));  
            socklen_t len = sizeof(client_addr);  
        printf("waiting for client.......\n");
            client_st = accept(st, (struct sockaddr*) &client_addr, &len);  
            if (client_st == -1)  
            {  
                printf("accept failed %s\n", strerror(errno));  
                return EXIT_FAILURE;  
            }  
            printf("accept by %s\n", inet_ntoa(client_addr.sin_addr));  
            pthread_create(&thrd1, NULL, recvsocket, &client_st);  
            pthread_create(&thrd2, NULL, sendsocket, &client_st);  
        }  
        close(st);  
        return 0;  
    }  

客戶端 client.c

    #include <stdio.h>  
    #include <stdlib.h>  
    #include <string.h>  
    #include <unistd.h>  
    #include <errno.h>  
    #include <sys/types.h>  
    #include <sys/socket.h>  
    #include <netinet/in.h>  
    #include <arpa/inet.h>  
    #include <pthread.h>  

    void* recvsocket(void *ptr)  
    {  
        int fd = *(int *)ptr;  
        char str[1024];  

        while (1)  
        {  
            memset(str, 0, sizeof(str));  
            int numbytes = recv(fd, s, sizeof(str), 0);  
            if (numbytes <= 0)  
                break;  
            printf("%s\n", str);  
        }  
        return NULL;  
    }  

    void* sendsocket(void *ptr)  
    {  
        int fd = *(int *)ptr;  
        char str[1024];  

        while (1)  
        {  
            memset(s, 0, sizeof(str));  
            read(STDIN_FILENO, str, sizeof(str));  
            send(fd, str, strlen(str), 0);  
        }  

        return NULL;  
    }  
    int main(int arg, char *args[])  
    {  




        int port = 1234;  
        int st = socket(AF_INET, SOCK_STREAM, 0); 



    int opt = SO_REUSEADDR;
    setsockopt(st, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

        struct sockaddr_in addr; 
        memset(&addr, 0, sizeof(addr));  
        addr.sin_family = AF_INET; 
        addr.sin_port = htons(port);  
        addr.sin_addr.s_addr = htonl(INADDR_ANY); 


        if (bind(st, (struct sockaddr *) &addr, sizeof(addr)) == -1)  
        {  
            printf("bind failed %s\n", strerror(errno));  
            return EXIT_FAILURE;  
        }  


        if (listen(st, 20) == -1)  
        {  
            printf("listen failed %s\n", strerror(errno));  
            return EXIT_FAILURE;  
        }  
        printf("listen success\n");  




        int client_st = 0;  
        struct sockaddr_in client_addr;

        pthread_t thrd1, thrd2;  
        while (1)  
        {  
            memset(&client_addr, 0, sizeof(client_addr));  
            socklen_t len = sizeof(client_addr);  
        printf("waiting for client.......\n");
            client_st = accept(st, (struct sockaddr*) &client_addr, &len);  
            if (client_st == -1)  
            {  
                printf("accept failed %s\n", strerror(errno));  
                return EXIT_FAILURE;  
            }  
            printf("accept by %s\n", inet_ntoa(client_addr.sin_addr));  
            pthread_create(&thrd1, NULL, recvsocket, &client_st);  
            pthread_create(&thrd2, NULL, sendsocket, &client_st);  
        }  
        close(st);  
        return 0;  
    }        

建立兩個執行緒併發、並行地工作，分別進行傳送/接收資料，（其實僅用建立一個執行緒，在主執行緒也可以完成相應的傳送和接收），但是這樣也有一個缺點，那就是如果要在非同步通訊程式上擴充套件其他的功能，那麼接收資料的工作最好全部由接收資料的執行緒來完成，因為如果在其他執行緒中加入recv語句接收資料，那麼執行緒之間會爭搶資源，這樣就無法判斷是哪一個執行緒接收到了資料。