非阻塞TCP示例

上节我们介绍了阻塞TCP，它的坏处就是一旦收不到数据就卡在那边，导致整个线程都不能做其他事情了，如果将Socket设成非阻塞的形式，那么就可以在超时后继续运行其他任务。 TCP的非阻塞设置和UDP相同，设置成功后即可直接收发。 注意，不要将服务器的Socket id设成了非阻塞，那样服务端在调用accept等待客户端连接时将不再阻塞等待，而是超时返回，那样就无法接到客户端请求了，应该将accept返回的客户端Socket进行设置，这样在和客户端收发数据时就可以实现延时等待的效果了。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <unistd.h> //usleep
#define checkError(ret) do{if(-1==ret){printf("[%d]err:%s\n", __LINE__, strerror(errno));exit(1);}}while(0)


int main(int argc, char const *argv[])
{
    printf("this is tcp demo\n");
    int iSocketFd = socket(AF_INET, SOCK_STREAM, 0);
    checkError(iSocketFd);


    int re = 1;
    checkError(setsockopt(iSocketFd, SOL_SOCKET, SO_REUSEADDR, &re, sizeof(re)));
    struct sockaddr_in server_addr;  
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;  
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);        /*receive any address*/
    server_addr.sin_port = htons(7878);
    checkError(bind(iSocketFd, (struct sockaddr*)&server_addr, sizeof(server_addr)));
    checkError(listen(iSocketFd, 5));


    int iSockClient;
    struct sockaddr_in client_addr;
    memset(&client_addr, 0, sizeof(client_addr));
    socklen_t client_len = sizeof(client_addr);
reconnect:
    iSockClient = accept(iSocketFd, (struct sockaddr*)&client_addr, &client_len);
    checkError(iSockClient);    

    struct timeval timeout={2,5};//timeout
    checkError(setsockopt(iSockClient, SOL_SOCKET, SO_RCVTIMEO,&timeout,sizeof(timeout)));
    //checkError(fcntl(iSockClient, F_SETFL, (fcntl(iSockClient, F_GETFL) | O_NONBLOCK)));//set noblock
    printf("client ipaddr:%s\n", inet_ntoa(client_addr.sin_addr));


    const char *aSend = "This is tcp server";
    char aRecv[2048] = {0}; 
    while(1)
    {
        printf("wait client data...\n");
        int irecv = recv(iSockClient, aRecv, sizeof(aRecv), 0);
        if(-1 == irecv){
            printf("recv err:%s\n", strerror(errno));
            if(errno == EAGAIN){
                usleep(100);
                continue;
            } else {
                exit(1);
            }
        } else if (0 == irecv){
            printf("disconnect with client\n");
            close(iSockClient);
            goto reconnect;
        }
        printf("recv client ip:%s, data:%s\n", inet_ntoa(client_addr.sin_addr), aRecv);
        checkError(send(iSockClient, aSend, strlen(aSend), 0));
        sleep(1);
    }
    return 0;
}

客户端程序我们使用的阻塞TCP做的实验，不再赘述。