c - TCP Linux 服务器在第一次接受后锁定

Question

我正在用 C 语言编写一个 TCP 客户端。按照几个教程，我编写了代码，但它只能接受与服务器的第一次连接。

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h> //inet_addr for INADDR_ANY
#include <string.h> //for splitting (strtok)
#include <pthread.h> //thread library
#include <time.h>
#include <unistd.h> //for function close()

void* SocketHandler(void*);


int main(void) {
    //socket parameters
    int server_socket_desc;
    int clientAddressLength = sizeof(struct sockaddr_in);
    struct sockaddr_in server_addr, client_addr;

    const unsigned short int PORT_NUMBER = 8963;
server_socket_desc = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (server_socket_desc < -1) {
        printf("Could not create socket");
    }
    puts("Socket created");

    //Prepare the sockaddr_in structure
    server_addr.sin_family = AF_INET;  //it should be always set to AF_INET
    //set the server address
    server_addr.sin_addr.s_addr = inet_addr("192.168.123.240");
    //server_addr.sin_addr.s_addr = inet_addr("31.185.101.35");
    //server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    server_addr.sin_port = htons(PORT_NUMBER);

    //Bind
    if (bind(server_socket_desc, (struct sockaddr *) &server_addr,
            sizeof(server_addr)) < 0) {
        //print the error message
        perror("bind failed. Error");
        return 1;
    }
    puts("bind done");

    //Listen
    listen(server_socket_desc, 10);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");

    //accept connection from an incoming client
    while (1) {
        int *temp_socket_desc = (int*) malloc(sizeof(int));
        if ((*temp_socket_desc = accept(server_socket_desc,
                (struct sockaddr *) &client_addr,
                (socklen_t*) &clientAddressLength)) != -1) {

            printf("----------\nConnection accepted \n");
            sleep(1);
            pthread_t thread_id;
            int *client_socket_desc = (int*) malloc(sizeof(int));
            client_socket_desc = temp_socket_desc;

            pthread_create(&thread_id, NULL, &SocketHandler,
                    (void*)     client_socket_desc);
            //if thread has not terminated, pthread_detach() shall not cause it to terminate
            pthread_detach(thread_id);
            puts("handler assigned");

        } else
            puts("connection refused");

    }

    close(server_socket_desc);
    //mysql_close(mysql_conn);
    return 0;
}

/*
 * This will handle connection for each client
 * */
void* SocketHandler(void* lp) {
    int *csock = (int*) lp;

    char buffer[128];
    int buffer_len = 128;
    int bytecount;
    memset(buffer, 0, buffer_len);
    if ((bytecount = read(*csock, buffer, buffer_len) == -1)) {
        fprintf(stderr, "Error receiving data\n");
        close(*csock);
        return 0;
    }
    printf("Received bytes %d\nReceived string \"%s\"\n", bytecount, buffer);

    close(*csock);
    free(csock);
    puts("exiting thread");
    //pthread_exit(0);
    return 0;
}

我暂时解决了在 while 循环之后插入 sleep() 的问题，但这是一个非常糟糕的解决方案。有人可以解释一下为什么代码在没有 sleep 的情况下无法工作吗？

Answer 1

处理 client_socket_desc 时出现问题:

您只分配一次。所有线程将获得相同的指针。因此稍后的接受将覆盖早期线程的套接字描述符值。

尝试以下更改，为每个线程分配自己的内存块:

int fd = accept( server_socket_desc, (struct sockaddr *) &client_addr, (socklen_t*)                
                 &clientAddressLength)
if ( fd != -1 ) 
{           
    pthread_t thread_id;
    int *client_socket_desc = malloc(sizeof(int));

    *client_socket_desc = fd;

    pthread_create(&thread_id, NULL, &SocketHandler,(void*) client_socket_desc);
    ...

或者当然您必须为 malloc 和 pthread_create 添加错误处理。并且在不再需要时释放分配的内存。

我不明白为什么while循环中有下面的代码:

if(send(*client_socket_desc,buffer,1,MSG_NOSIGNAL)>0)
{
    puts("closing client socket");
    close(*client_socket_desc);
}

关闭客户端处理程序线程中的客户端套接字。