Question

我在处理多个客户端并从中接收消息而没有阻止每个操作时，让select（）正常工作时遇到了问题。

我了解到select确定了一个或多个套接字的状态，因此每次接受连接时，我都会将套接字置于集合中，使用宏确定哪个可以读取。我发现我的代码永远不会进入accept_clients（）函数。我想，如果有人查看我的代码并帮助其完成工作。

这是我的代码。

#pragma comment(lib, "ws2_32.lib")
#include <WinSock2.h>
#include <stdio.h>
#include <signal.h>
#include <conio.h>
#include <assert.h>
#include <Windows.h>
#include <iostream>
//sockets
#define CLIENT_CON 10
#define CLIENT_DIS 20
#define BF_SZ 100
#define MAX_CONS 5
#define TIMEVAL_SEC 0
#define TIMEVAL_USEC 10
SOCKET sock, clien;
int PR_CONS = 0;

 struct _client
{
    bool con; // Set true if a client is connected
    sockaddr_in addr; // Client info like ip address
    SOCKET cs; // Client socket
    //fd_set set; // used to check if there is data in the socket
    int i; // any piece of additional info
};
_client client[10];
fd_set sset;

 int accept(_client*);
 int recv(_client*, char*, int);
 void Server_Status(int );
 void accept_clients();
 void recv_client();
int main() {
    //int res;
    int i = 1;
    int port = 5150;
    WSADATA ws;
    printf("\t Echo Server (Multiple client support)\n");
    sockaddr_in ser;
    ser.sin_family = AF_INET;
    ser.sin_addr.S_un.S_addr = INADDR_ANY;
    ser.sin_port = htons(port);
    WSAStartup(MAKEWORD(2,2),&ws);

    sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&i,sizeof(i));
    bind(sock,(SOCKADDR*)&ser, sizeof(ser));
    listen(sock,5);
    printf("listening \n");
    unsigned long b= 1;
    ioctlsocket(sock,FIONBIO,&b);

    for(int i = 0; i < MAX_CONS; i++) {
        client[i].con = false;
    }
    while(true) {
        accept_clients();
        recv_client();
    }

}
 int accept(_client* x) {
     x->i = sizeof(sockaddr_in);
     int isClient = 0;
     unsigned long b= 1;
     FD_ZERO(&sset);
     FD_SET(sock, &sset);
     isClient = select(0, &sset, NULL,NULL, 0);
     if(isClient > 0 && PR_CONS <  MAX_CONS) {
         x->cs = accept(sock, (SOCKADDR*)&x->addr, &x->i);
         ioctlsocket(x->cs,FIONBIO,&b);
             if(x->cs != INVALID_SOCKET ) {
             x->con = true;
             FD_ZERO(&sset);
             FD_SET(x->cs,&sset);
             return true;
         }
     }
     //printf("failed to accept client");
     return false;
 }

 int recv(_client *x, char* buffer, int sz) {
     int r;
     /*timeval timeOut;
     timeOut.tv_sec = TIMEVAL_SEC;
     timeOut.tv_usec = TIMEVAL_USEC;*/
     r = select(0,&sset, NULL,NULL,0);
    if(r >  0) {
        if((FD_ISSET(x->cs,&sset)) ) {
            x->i = recv(x->cs,buffer,sz, 0);
            if(x->i > 0) {
                Server_Status(CLIENT_DIS);
                FD_CLR(x->cs,&sset);
                return 0;
            }
            return true;
          }
        }
         return false;
 }

 void accept_clients() {
     for(int i = 0; i < MAX_CONS;  i++) {
         if(!client[i].con) {
            if(accept(&client[i])) {
                Server_Status(CLIENT_CON);
            }
        }
    }
 }
void Server_Status(int msg) {
    if(msg == CLIENT_CON) {
        PR_CONS++;
        printf("client has connected");
    }
    else if(msg == CLIENT_DIS) {
        PR_CONS--;
        printf("client has disconnected");
    }
    else {
        printf("we got unknown message");
    }
}


void recv_client() {
    printf("problem?");
    char buffer[BF_SZ];
    for(int i = 0; i < MAX_CONS; i++) {
        if(client[i].con) {
            if(recv(&client[i],buffer, BF_SZ)) {
                std::cout << buffer << std::endl;
            }
        }
    }

}

Answer 1

除非客户端数量固定（总是MAX_CONS）客户端，并且在它们全部连接之前无法交换任何内容，否则您将误用select。

更常见的用法是（伪代码）

s = listening_socket
put s in a fd_set
loop on select
   if s is ready for read:
      new_con = accept
      store new_con in a client array
      put s in the fd_set
   else
      find one element of the read-ready set other than s (*)
      recv data from that client
      process data

（*）你可以从第一个元素开始，在这种情况下，第一个客户端将具有稍高的优先级，或者在最后一个使用的元素之后开始并且在最后一个之后回滚（循环）以给予所有客户端相同的优先级

使用select（）管理多个套接字

1 个答案: