Linux C++ TCP通信基于poll 和 select模型

wrap.h 

#ifndef __WRAP_H_
#define __WRAP_H_

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>

void perr_exit(const char *s);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
int Bind(int fd, const struct sockaddr *sa, socklen_t salen);
int Connect(int fd, const struct sockaddr *sa, socklen_t salen);
int Listen(int fd, int backlog);
int Socket(int family, int type, int protocol);
ssize_t Read(int fd, void *ptr, size_t nbytes);
ssize_t Write(int fd, const void *ptr, size_t nbytes);
int Close(int fd);
ssize_t Readn(int fd, void *vptr, size_t n);
ssize_t Writen(int fd, const void *vptr, size_t n);
ssize_t my_read(int fd, char *ptr);
ssize_t Readline(int fd, void *vptr, size_t maxlen);

#endif // __WRAP_H_

wrap.cpp

#include "wrap.h"

void perr_exit(const char *s)
{
    perror(s);
    exit(-1);
}

int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
{
    int n;

again:
    if ((n = accept(fd, sa, salenptr)) < 0)
    {
        if ((errno == ECONNABORTED) || (errno == EINTR))
        {
            goto again;
        }
        else
        {
            perr_exit("accept error");
        }
    }
    return n;
}

int Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
    int n;

    if ((n = bind(fd, sa, salen)) < 0)
        perr_exit("bind error");

    return n;
}

int Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
    int n;
    n = connect(fd, sa, salen);
    if (n < 0) {
        perr_exit("connect error");
    }

    return n;
}

int Listen(int fd, int backlog)
{
    int n;

    if ((n = listen(fd, backlog)) < 0)
        perr_exit("listen error");

    return n;
}

int Socket(int family, int type, int protocol)
{
    int n;

    if ((n = socket(family, type, protocol)) < 0)
        perr_exit("socket error");

    return n;
}

ssize_t Read(int fd, void *ptr, size_t nbytes)
{
    ssize_t n;

again:
    if ( (n = read(fd, ptr, nbytes)) == -1) {
        if (errno == EINTR)
            goto again;
        else
            return -1;
    }

    return n;
}

ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
    ssize_t n;

again:
    if ((n = write(fd, ptr, nbytes)) == -1) {
        if (errno == EINTR)
            goto again;
        else
            return -1;
    }
    return n;
}

int Close(int fd)
{
    int n;
    if ((n = close(fd)) == -1)
        perr_exit("close error");

    return n;
}

/*参三: 应该读取的字节数*/                          //socket 4096  readn(cfd, buf, 4096)   nleft = 4096-1500
ssize_t Readn(int fd, void *vptr, size_t n)
{
    size_t  nleft;              //usigned int 剩余未读取的字节数
    ssize_t nread;              //int 实际读到的字节数

    char *ptr = (char*)vptr;
    // n 未读取字节数
    nleft = n;

    while (nleft > 0) {
        if ((nread = read(fd, ptr, nleft)) < 0) {
            if (errno == EINTR)
                nread = 0;
            else
                return -1;
        } else if (nread == 0)
            break;

        nleft -= nread;   //nleft = nleft - nread 
        ptr += nread;
    }
    return n - nleft;
}

ssize_t Writen(int fd, const void *vptr, size_t n)
{
    size_t nleft;
    ssize_t nwritten;


    const char *ptr = (const char*)vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
            if (nwritten < 0 && errno == EINTR)
                nwritten = 0;
            else
                return -1;
        }
        nleft -= nwritten;
        ptr += nwritten;
    }
    return n;
}

ssize_t my_read(int fd, char *ptr)
{
    static int read_cnt;
    static char *read_ptr;
    static char read_buf[100];

    if (read_cnt <= 0)
    {
again:
        if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {   //"hello
"
            if (errno == EINTR)
                goto again;
            return -1;
        } else if (read_cnt == 0)
            return 0;

        read_ptr = read_buf;
    }
    read_cnt--;
    *ptr = *read_ptr++;

    return 1;
}

/*readline --- fgets*/    
//传出参数 vptr
ssize_t Readline(int fd, void *vptr, size_t maxlen)
{
    ssize_t n, rc;
    char c;
    char *ptr = (char*)vptr;

    for (n = 1; n < maxlen; n++) {
        if ((rc = my_read(fd, &c)) == 1) {   //ptr[] = hello

            *ptr++ = c;
            if (c == '
')
                break;
        } else if (rc == 0) {
            *ptr = 0;
            return n-1;
        } else
            return -1;
    }
    *ptr = 0;

    return n;
}

客户端代码

#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <time.h>
#include <iostream>
using namespace std;

#include "wrap.h"

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666

char *randstr(char *str, const int len)
{
    srand(time(NULL));
    int i;
    for (i = 0; i < len; ++i)
    {
        switch ((rand() % 3))
        {
        case 1:
            str[i] = 'A' + rand() % 26;
            break;
        case 2:
            str[i] = 'a' + rand() % 26;
            break;
        default:
            str[i] = '0' + rand() % 10;
            break;
        }
    }
    str[++i] = '';
    return str;
}

int main(void)
{
    char buf[BUFSIZ];
    // 创建 TCP 套接字
    int sfd = Socket(AF_INET, SOCK_STREAM, 0);

    sockaddr_in serv_addr;
    bzero(&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;

    // 将文本字符串格式转换成网络字节序的二进制地址
    inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr.s_addr);
    // 返回以网络字节序表示的16位整数
    serv_addr.sin_port = htons(SERV_PORT);

    Connect(sfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));

    while (true)
    {
        randstr(buf, 5);
        string str = "PID = ";
        str.append(to_string(getpid()));
        str.append(", ");
        str.append(buf);
        int r = Write(sfd, str.c_str(), str.size());
        cout << "PID = " << getpid() << ", Write len = " << r << endl;
        int len = Read(sfd, buf, sizeof(buf));
        cout << "PID = " << getpid() << ", Read len = " << len << endl;
        cout << buf << endl << endl;

        sleep(rand() % 3 + 1);
    }

    // 关闭套接字
    Close(sfd);

    return 0;
}

服务器代码

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <poll.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <iostream>
using namespace std;

#include "wrap.h"

#define MAXLINE 80
#define SERV_PORT 6666
#define OPEN_MAX 1024

/**** 1.select 模型　****/
// (1) select能监听的文件描述符个数受限于FD_SETSIZE,一般为1024，单纯改变进程打开的文件描述符个数并不能改变select监听文件个数．
// (2)解决1024以下客户端时使用select是很合适的，但如果链接客户端过多，select采用的是轮询模型，会大大降低服务器响应效率，不应在select上投入更多精力．
void testSelect()
{
    int i, maxi;

    // 自定义数组client, 防止遍历1024个文件描述符  FD_SETSIZE默认为1024
    int client[FD_SETSIZE];
    int listenfd, connfd, sockfd;
    char buf[BUFSIZ], str[INET_ADDRSTRLEN];         /* #define INET_ADDRSTRLEN 16 */

    struct sockaddr_in clie_addr, serv_addr;
    socklen_t clie_addr_len;
    fd_set rset, allset;                            /* rset 读事件文件描述符集合 allset用来暂存 */

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);

    int opt = 1;
    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    bzero(&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family= AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port= htons(SERV_PORT);

    Bind(listenfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
    Listen(listenfd, 128);

    // 将来用作client[]的下标, 初始值指向0个元素之前下标位置
    maxi = -1;
    for (i = 0; i < FD_SETSIZE; i++)
    {
        /* 用-1初始化client[] */
        client[i] = -1;
    }


    FD_ZERO(&allset);
    // 构造select监控文件描述符集
    FD_SET(listenfd, &allset);
    // 起初 listenfd 即为最大文件描述符
    int maxfd = listenfd;

    while(true)
    {
        /* 每次循环时都从新设置select监控信号集 */
        rset = allset;
        int nready = select(maxfd + 1, &rset, NULL, NULL, NULL);
        if (nready < 0)
        {
            perror("select error");
            exit(-1);
        }

        if (FD_ISSET(listenfd, &rset))
        {
            // 说明有新的客户端链接请求
            clie_addr_len = sizeof(clie_addr);
            connfd = Accept(listenfd, (struct sockaddr *)&clie_addr, &clie_addr_len);       /* Accept 不会阻塞 */
            printf("received from %s at PORT %d
", inet_ntop(AF_INET, &clie_addr.sin_addr, str, sizeof(str)), ntohs(clie_addr.sin_port));

            for (i = 0; i < FD_SETSIZE; i++)
            {
                if (client[i] < 0)
                {
                    // 找client[]中没有使用的位置,保存accept返回的文件描述符到client[]里
                    client[i] = connfd;
                    break;
                }
            }


            if (i == FD_SETSIZE)
            {
                // 达到select能监控的文件个数上限 1024
                fputs("too many clients
", stderr);
                exit(1);
            }

            // 向监控文件描述符集合allset添加新的文件描述符connfd
            FD_SET(connfd, &allset);
            if (connfd > maxfd)
            {
                maxfd = connfd;
            }


            // 保证maxi存的总是client[]最后一个元素下标
            if (i > maxi)
            {
                maxi = i;
            }

            nready--;
            if (nready == 0)
            {
                continue;
            }
        }

        for (i = 0; i <= maxi; i++)
        {
            // 检测哪个clients 有数据就绪
            if ((sockfd = client[i]) < 0)
            {
                continue;
            }

            if (FD_ISSET(sockfd, &rset))
            {
                int n = Read(sockfd, buf, sizeof(buf));
                if (n == 0)
                {
                    // 当client关闭链接时,服务器端也关闭对应链接
                    Close(sockfd);
                    // 解除select对此文件描述符的监控
                    FD_CLR(sockfd, &allset);
                    client[i] = -1;
                }
                else if (n > 0)
                {
                    for (int j = 0; j < n; j++)
                    {
                        // 把小写字母转换为大写字母
                        buf[j] = toupper(buf[j]);
                    }
                    Write(sockfd, buf, n);
                    cout << buf << endl;
                }

                nready--;
                if (nready == 0)
                {
                    // 跳出for循环, 但还在while循环中
                    break;
                }
            }
        }
    }
    Close(listenfd);
}

/**** 2.poll 模型　****/
void testPoll()
{
    int i, listenfd, connfd, sockfd;

    char buf[MAXLINE], str[INET_ADDRSTRLEN];
    socklen_t clilen;
    struct sockaddr_in cliaddr, servaddr;

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);

    // 端口復用
    int opt = 1;
    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);

    Bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
    Listen(listenfd, 128);

    struct pollfd client[OPEN_MAX];
    // 要监听的第一个文件描述符 存入client[0]
    client[0].fd = listenfd;
    // listenfd监听普通读事件
    client[0].events = POLLIN;

    for (i = 1; i < OPEN_MAX; i++)
    {
        // 用-1初始化client[]里剩下元素,0也是文件描述符,不能用
        client[i].fd = -1;
    }

    // client[]数组有效元素中最大元素下标
    int maxi = 0;

    while(true)
    {
        // 阻塞监听是否有客户端链接请求
        int nready = poll(client, maxi+1, -1);

        // listenfd有读事件就绪
        if (client[0].revents & POLLIN)
        {
            clilen = sizeof(cliaddr);
            // 接收客户端请求 Accept 不会阻塞
            connfd = Accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
            printf("received from %s at PORT %d
", inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port));

            for (i = 1; i < OPEN_MAX; i++)
            {
                if (client[i].fd < 0)
                {
                     // 找到client[]中空闲的位置,存放accept返回的connfd
                    client[i].fd = connfd;
                    break;
                }
            }

            if (i == OPEN_MAX)
            {
                // 达到了最大客户端数
                perr_exit("too many clients");
            }

            // 设置刚刚返回的connfd,监控读事件
            client[i].events = POLLIN;
            if (i > maxi)
            {
                // 更新client[]中最大元素下标
                maxi = i;
            }

            nready--;
            if (nready == 0)
            {
                // 没有更多就绪事件时,继续回到poll阻塞
                continue;
            }
        }

        for (i = 1; i <= maxi; i++)
        {
            // 前面的if没满足,说明没有listenfd满足. 检测client[] 看是那个connfd就绪
            if ((sockfd = client[i].fd) < 0)
            {
                continue;
            }

            if (client[i].revents & POLLIN)
            {
                ssize_t n = Read(sockfd, buf, MAXLINE);
                if (n < 0)
                {
                    // connection reset by client
                    if (errno == ECONNRESET)
                    {
                        /* 收到RST标志 */
                        printf("client[%d] aborted connection
", i);
                        Close(sockfd);
                        // poll中不监控该文件描述符,直接置为-1即可,不用像select中那样移除
                        client[i].fd = -1;
                    }
                    else
                    {
                        perr_exit("read error");
                    }
                }
                else if (n == 0)
                {
                    // 说明客户端先关闭链接
                    printf("client[%d] closed connection
", i);
                    Close(sockfd);
                    client[i].fd = -1;
                }
                else
                {
                    for (int j = 0; j < n; j++)
                    {
                        buf[j] = toupper(buf[j]);
                    }
                    Writen(sockfd, buf, n);
                    cout << buf << endl;
                }

                nready--;
                if (nready == 0)
                {
                    // 跳出for循环, 但还在while循环中
                    break;
                }
            }
        }
    }
    return;
}

int main()
{
    testPoll();
    return 0;
}
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原文地址：https://www.cnblogs.com/duxie/p/15091595.html