套接字超時處理的三種方法

一、使用SIGALRM爲connect 設置超時

signal  捕捉到alarm信號之後會中斷connect函數，導致返回值爲EINTR，因此可提前設置connect超時返回，而不用等到最長 75s的connect原始超時時長

1、Signal 返回值 爲  typede void Sigfunc(int);    -- 可以保存和恢復舊的信號處理函數

2、alarm(); 可覆蓋之前的定時，返回值爲 之前定時的剩餘時間，返回0表示之前未設置定時

3、connect()  返回 < 0，設置爲失敗,超時; 若成功, == 0；connect失敗後需關閉close(sockfd);並重新 socket() 獲取套接字

/* include connect_timeo */
#include    "unp.h"

static void connect_alarm(int);

int
connect_timeo(int sockfd, const SA *saptr, socklen_t salen, int nsec)
{
    Sigfunc *sigfunc;
    int     n;  

    sigfunc = Signal(SIGALRM, connect_alarm);
    if (alarm(nsec) != 0)
        err_msg("connect_timeo: alarm was already set");

    if ( (n = connect(sockfd, saptr, salen)) < 0) {
        close(sockfd);
        if (errno == EINTR)
            errno = ETIMEDOUT;
    }   
    alarm(0);                   /* turn off the alarm */
    Signal(SIGALRM, sigfunc);   /* restore previous signal handler */

    return(n);
}

static void
connect_alarm(int signo)
{
    return;     /* just interrupt the connect() */
}
/* end connect_timeo */

void
Connect_timeo(int fd, const SA *sa, socklen_t salen, int sec)
{
    if (connect_timeo(fd, sa, salen, sec) < 0)
        err_sys("connect_timeo error");             // 出錯或者超時 都 < 0

    // 連接成功 connect_timeo 返回 0
}

二、使用select爲accept 設置超時

fd_set fdset;
struct timeval tv;

FD_ZERO(&fdset);
FD_SET(info->sockfd, &fdset);
    
tv.tv_sec = 9;
tv.tv_usec = 0;

iRet = select(info->sockfd + 1, &fdset, NULL, NULL, &tv);
if (iRet > 0)
{
    /*成功則爲非負描述符*/
    connfd = accept(info->sockfd, (struct sockaddr *)&cliAddr, &iAddrLen);
    if (connfd < 0)
    {
        printf("[%s %d] accept failed. \r\n", __FILE__, __LINE__);
        return -1;
    }
    else
    {
        info->connfd = connfd;
        printf("[%s %d] accept succ. connfd = %d\r\n", __FILE__, __LINE__, connfd);
        return 0;
    }
}
else
{
    printf("[%s %d] select timeout or Failed\r\n", __FILE__, __LINE__);
    return -1;
}

 

 

三、使用setsockopt設置SO_RCVTIMEO爲recvfrom設置超時

errno == EWOULDBLOCK

#include    "unp.h"

void
dg_cli(FILE *fp, int sockfd, const SA *pservaddr, socklen_t servlen)
{
    int             n;  
    char            sendline[MAXLINE], recvline[MAXLINE + 1]; 
    struct timeval  tv; 

    tv.tv_sec = 5;
    tv.tv_usec = 0;
    Setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));

    while (Fgets(sendline, MAXLINE, fp) != NULL) {

        Sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen);

        n = recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL);
        if (n < 0) {
            if (errno == EWOULDBLOCK) {
                fprintf(stderr, "socket timeout\n");
                continue;
            } else
                err_sys("recvfrom error");
        }   

        recvline[n] = 0;    /* null terminate */
        Fputs(recvline, stdout);
    }   
}