Linux下非阻塞connect

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <time.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <string.h>

#define BUFFER_SIZE 1023

int setnonblocking(int fd)
{
    int old_option=fcntl(fd,F_GETFL);
    int new_option=old_option | O_NONBLOCK;
    fcntl(fd,F_SETFL,new_option);
    return old_option;
}

int unblock_connect(const char *ip,int port,int time)
{
    int ret=0;
    struct sockaddr_in address;
    bzero(&address,sizeof(address));
    address.sin_family=AF_INET;
    inet_pton(AF_INET,ip,&address.sin_addr);
    address.sin_port=htons(port);

    int sockfd=socket(PF_INET,SOCK_STREAM,0);
    int fdopt=setnonblocking(sockfd);
    ret=connect(sockfd,(struct sockaddr *)&address,sizeof(address));
    if(ret==0)
    {
        printf("connect with server immediately\n");
        fcntl(sockfd,F_SETFL,fdopt);
        return sockfd;
    }
    else if(errno!=EINPROGRESS)
    {
        printf("unblock connect not support\n");
        return -1;
    }
    fd_set readfds;
    fd_set writefds;
    struct timeval timeout;
    timeout.tv_sec=time;
    timeout.tv_usec=0;

    ret=select(sockfd+1,NULL,&writefds,NULL,&timeout);
    if(ret<=0)
    {
        printf("connection time out\n");
        close(sockfd);
        return -1;
    }
    if(!FD_ISSET(sockfd,&writefds))
    {
        printf("no events on sockfd found\n");
        close(sockfd);
        return -1;
    }

    int error=0;
    socklen_t length=sizeof(error);
    if(getsockopt(sockfd,SOL_SOCKET,SO_ERROR,&error,&length)<0)
    {
        printf("get socket option failed");
        close(sockfd);
        return -1;
    }
    if(error!=0)
    {
        printf("connection failed after select with the error:% d \n",error);
        close(sockfd);
        return -1;
    }
    printf("connection ready after select with the socket:  %d \n",sockfd);
    fcntl(sockfd,F_SETFL,fdopt);
    return sockfd;
}

int main()
{
    const char *ip="127.0.0.1";
    int port=12345;
    int sockfd=unblock_connect(ip,port,10);
    if(sockfd<0)
    {
        return 1;
    }
    close(sockfd);
    return 0;
}