Socket for Linux network programming (12) example of concurrent restriction of select function and application of poll function

The concurrent server, which can be achieved with select, is limited by two aspects.

1, a process can open the maximum file descriptor restrictions. This can be done by adjusting the kernel parameters. You can adjust or use the Setrlimit function setting by ulimit-n, but the maximum number that a system can open is also limited, which is related to memory size and can be viewed by Cat/proc/sys/fs/file-max

2, the Fd_set set capacity limit in the Select (Fd_setsize, typically 1024), which requires recompiling the kernel.

You can write a test program that only establishes a connection to see how many connections can be established, and the client program is as follows:

 #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/ inet.h> #include <signal.h> #include <stdlib.h> #include <stdio.h> #include <errno.h> #inc Lude <string.h> #define ERR_EXIT (m) \ do \ {\ perror (m); \ Exi T (exit_failure);
    \} while (0) int main (void) {int count = 0;
        while (1) {int sock;
            if ((sock = socket (pf_inet, Sock_stream, ipproto_tcp)) < 0) {sleep (4);
        Err_exit ("socket");
        } struct sockaddr_in servaddr;
        memset (&servaddr, 0, sizeof (SERVADDR));
        servaddr.sin_family = af_inet;
        Servaddr.sin_port = htons (5188);
    
        SERVADDR.SIN_ADDR.S_ADDR = inet_addr ("127.0.0.1");
    
        if (Connect (sock, (struct sockaddr *) &servaddr, sizeof (SERVADDR)) < 0) Err_exit ("Connect"); structSockaddr_in localaddr;
        socklen_t Addrlen = sizeof (LOCALADDR);
    
        if (getsockname (sock, struct sockaddr *) &localaddr, &addrlen) < 0) Err_exit ("GetSockName");
        printf ("ip=%s port=%d\n", Inet_ntoa (LOCALADDR.SIN_ADDR), Ntohs (Localaddr.sin_port));
    
    printf ("Count =%d\n", ++count);
return 0; }