TCP客户端非阻塞connect，EPOLL异步响应

废话不多说，直接上代码
下面展示一些 内联代码片。

#include <sys/types.h>  
#include <sys/socket.h>  
#include <netinet/in.h>  
#include <arpa/inet.h>  
#include <unistd.h>  
#include <stdlib.h>  
#include <stdio.h>
#include <iostream>
#include <string>
#include <string.h>
#include <fcntl.h>
#include <error.h>
#include <sys/epoll.h>
#include <pthread.h>

using namespace std;
  
#define PORT 9734

int g_epollfd = 0;

void *epollthread(void *arg)
{
	struct epoll_event events[100];
	int ret;
	while (true) {
		ret = epoll_wait(g_epollfd, events, sizeof(events), 1000);
		if (ret > 0) {
			for (int i=0;i<ret;i++) {
				if (events[i].events & EPOLLERR) {
					printf("EPOLLERR exists\n");
					// 通过 socket 获取具体失败原因
					int error;
					socklen_t error_len = sizeof(int);
					ret = getsockopt(events[i].data.fd, SOL_SOCKET, SO_ERROR, &error, &error_len);
					printf("getsockopt connect failed, errno: [%d] %s\n", error, strerror(error));
				} else {
					printf("connect successful!!!\n");
				}
				epoll_ctl(g_epollfd, EPOLL_CTL_DEL, events[i].data.fd, NULL);
			}
		} else if (ret == 0) {
			printf("epoll timeout\n");
		}
	}
    printf( "This is a thread\n");
	return NULL;
}

void nonblockingConnect(const char* ip, short port)
{
	int clientFD = socket(AF_INET, SOCK_STREAM, 0);
	if (clientFD == -1) {
		printf("create socket failed\n");
		return;
	}
 
    //设置非阻塞
	int flag = fcntl(clientFD, F_GETFL, 0);
	if (fcntl(clientFD, F_SETFL, flag | SOCK_NONBLOCK) == -1) {
		printf("fcntl failed\n");
		close(clientFD);
		return;
	}
 
	struct sockaddr_in srvAddr;
	memset(&srvAddr, 0, sizeof(struct sockaddr_in));
	srvAddr.sin_addr.s_addr = inet_addr(ip);
	srvAddr.sin_port = htons(port);
	srvAddr.sin_family = AF_INET;
 
    //为了处理EINTR,将connect放在循环内
    while (1) {
        int ret = connect(clientFD, (sockaddr*)&srvAddr, sizeof(struct sockaddr_in));
        if (ret == 0) {
            cout << "connect successfully" << endl;
            return;
        } else if (ret == -1) {
			// 非阻塞 connect 一般都是返回 -1 ， errno 设置为 EINPROGRESS
            if (errno == EINTR) {
                cout << "signal interrupt" << endl;
                continue;
            } else if (errno != EINPROGRESS) {
                cout << "can not connect to server, errno: " << errno << endl;
                close(clientFD);
                return;
            } else {
				struct epoll_event ev;
				ev.events = EPOLLOUT | EPOLLERR;
				ev.data.fd = clientFD;
				epoll_ctl(g_epollfd, EPOLL_CTL_ADD, clientFD, &ev);
                return;
            }
        }
    }
	return;
}

int main()
{
	g_epollfd = epoll_create(10);
    pthread_t thread_one;
    int ret;
    ret = pthread_create(&thread_one, NULL, epollthread, NULL);  
    if (ret != 0) {
        printf( "Create thread error!\n");  
        return -1;
    }

	nonblockingConnect("127.0.0.1", PORT);

	printf("This is the main process.\n");
    pthread_join(thread_one, NULL);
	return 0;  
}