Linux下的异步TCP socket及实例

• 同步socket通讯时，程序会阻塞在诸如(connect、accept、recv、recvfrom)等操作上，直到有事件发生时才会继续。
• 而在异步通讯交互中，两方可以任意发送消息，当有数据要接收时，会收到系统消息提示来接收数据，而不会阻塞。
• 在Linux下基于socket的异步通讯可以有多种方式，比较常用的有select方式、epoll方式和异步消息的方式。

 

一、 select方式：

1. 设置放置socket句柄的集合变量
2. 把要判断的socket句柄放到集合
3. 设置超时时间
4. 执行select操作
5. 根据select操作返回值做相应处理（连接、读、写等）

例子：

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#define MYPORT i        1234        // the port users will be connecting to#define BACKLOG         5           // how many pending connections queue will hold#define BUF_SIZE        200int fd_A[BACKLOG];                  // accepted connection fdint conn_amount;                    // current connection amountvoid showclient(){    int i;    printf("client amount: %d\n", conn_amount);    for (i = 0; i < BACKLOG; i++) {        printf("[%d]:%d  ", i, fd_A[i]);    }    printf("\n\n");}int main(void){    int sock_fd, new_fd;    // listen on sock_fd, new connection on new_fd    struct sockaddr_in server_addr;     // server address information    struct sockaddr_in client_addr;     // connector's address information    socklen_t sin_size;    int yes = 1;    char buf[BUF_SIZE];    int ret;    int i;    if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {        perror("socket");        exit(1);    }    if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {        perror("setsockopt");        exit(1);    }    server_addr.sin_family = AF_INET;         // host byte order    server_addr.sin_port = htons(MYPORT);     // short, network byte order    server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP    memset(server_addr.sin_zero, '', sizeof(server_addr.sin_zero));    if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {        perror("bind");        exit(1);    }    if (listen(sock_fd, BACKLOG) == -1) {        perror("listen");        exit(1);    }    printf("listen port %d\n", MYPORT);    fd_set fdsr;    int maxsock;    struct timeval tv;    conn_amount = 0;    sin_size = sizeof(client_addr);    maxsock = sock_fd;    while (1) {        // initialize file descriptor set        FD_ZERO(&fdsr);        FD_SET(sock_fd, &fdsr);        // timeout setting        tv.tv_sec = 30;        tv.tv_usec = 0;        // add active connection to fd set        for (i = 0; i < BACKLOG; i++) {            if (fd_A[i] != 0) {                FD_SET(fd_A[i], &fdsr);            }        }        ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv);        if (ret < 0) {            perror("select");            break;        } else if (ret == 0) {            printf("timeout\n");            continue;        }        // check every fd in the set        for (i = 0; i < conn_amount; i++) {            if (FD_ISSET(fd_A[i], &fdsr)) {                ret = recv(fd_A[i], buf, sizeof(buf), 0);                if (ret <= 0) {        // client close                    printf("client[%d] close\n", i);                    close(fd_A[i]);                    FD_CLR(fd_A[i], &fdsr);                    fd_A[i] = 0;                }                else {        // receive data                    if (ret < BUF_SIZE)                        memset(&buf[ret], '', 1);                    printf("client[%d] send:%s\n", i, buf);                }            }        }        // check whether a new connection comes        if (FD_ISSET(sock_fd, &fdsr)) {            new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size);            if (new_fd <= 0) {                perror("accept");                continue;            }            // add to fd queue            if (conn_amount < BACKLOG) {                fd_A[conn_amount++] = new_fd;                printf("new connection client[%d] %s:%d\n", conn_amount,inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));                if (new_fd > maxsock)                    maxsock = new_fd;            }            else {                printf("max connections arrive, exit\n");                send(new_fd, "bye", 4, 0);                close(new_fd);                break;            }        }        showclient();    }    // close other connections    for (i = 0; i < BACKLOG; i++) {        if (fd_A[i] != 0) {            close(fd_A[i]);        }    }    return 0;}

 

二、 epool方式

1. 用epoll_create建立epool句柄
2. 控制socket行为epoll_ctl
3. 等待socket状态处理epoll_wait

例子：

#include <sys/socket.h>#include <sys/epoll.h>#include <netinet/in.h>#include <arpa/inet.h>#include <fcntl.h>#include <unistd.h>#include <stdio.h>#include <errno.h>#include <iostream>using namespace std;#define MAX_EVENTS 500struct myevent_s{    int fd;    void (*call_back)(int fd, int events, void *arg);    int events;    void *arg;    int status; // 1: in epoll wait list, 0 not in    char buff[128]; // recv data buffer    int len;    long last_active; // last active time};// set eventvoid EventSet(myevent_s *ev, int fd, void (*call_back)(int, int, void*), void *arg){    ev->fd = fd;    ev->call_back = call_back;    ev->events = 0;    ev->arg = arg;    ev->status = 0;    ev->last_active = time(NULL);}// add/mod an event to epollvoid EventAdd(int epollFd, int events, myevent_s *ev){    struct epoll_event epv = {0, {0}};    int op;    epv.data.ptr = ev;    epv.events = ev->events = events;    if(ev->status == 1){        op = EPOLL_CTL_MOD;    }    else{        op = EPOLL_CTL_ADD;        ev->status = 1;    }    if(epoll_ctl(epollFd, op, ev->fd, &epv) < 0)        printf("Event Add failed[fd=%d]\n", ev->fd);    else        printf("Event Add OK[fd=%d]\n", ev->fd);}// delete an event from epollvoid EventDel(int epollFd, myevent_s *ev){    struct epoll_event epv = {0, {0}};    if(ev->status != 1) return;    epv.data.ptr = ev;    ev->status = 0;    epoll_ctl(epollFd, EPOLL_CTL_DEL, ev->fd, &epv);}int g_epollFd;myevent_s g_Events[MAX_EVENTS+1]; // g_Events[MAX_EVENTS] is used by listen fdvoid RecvData(int fd, int events, void *arg);void SendData(int fd, int events, void *arg);// accept new connections from clientsvoid AcceptConn(int fd, int events, void *arg){    struct sockaddr_in sin;    socklen_t len = sizeof(struct sockaddr_in);    int nfd, i;    // accept    if((nfd = accept(fd, (struct sockaddr*)&sin, &len)) == -1)    {        if(errno != EAGAIN && errno != EINTR)        {            printf("%s: bad accept", __func__);        }        return;    }    do    {        for(i = 0; i < MAX_EVENTS; i++)        {            if(g_Events[i].status == 0)            {                break;            }        }        if(i == MAX_EVENTS)        {            printf("%s:max connection limit[%d].", __func__, MAX_EVENTS);            break;        }        // set nonblocking        if(fcntl(nfd, F_SETFL, O_NONBLOCK) < 0) break;        // add a read event for receive data        EventSet(&g_Events[i], nfd, RecvData, &g_Events[i]);        EventAdd(g_epollFd, EPOLLIN|EPOLLET, &g_Events[i]);        printf("new conn[%s:%d][time:%d]\n", inet_ntoa(sin.sin_addr), ntohs(sin.sin_port), g_Events[i].last_active);    }while(0);}// receive datavoid RecvData(int fd, int events, void *arg){    struct myevent_s *ev = (struct myevent_s*)arg;    int len;    // receive data    len = recv(fd, ev->buff, sizeof(ev->buff)-1, 0);    EventDel(g_epollFd, ev);    if(len > 0)    {        ev->len = len;        ev->buff[len] = '';        printf("C[%d]:%s\n", fd, ev->buff);        // change to send event        EventSet(ev, fd, SendData, ev);        EventAdd(g_epollFd, EPOLLOUT|EPOLLET, ev);    }    else if(len == 0)    {        close(ev->fd);        printf("[fd=%d] closed gracefully.\n", fd);    }    else    {        close(ev->fd);        printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno));    }}// send datavoid SendData(int fd, int events, void *arg){    struct myevent_s *ev = (struct myevent_s*)arg;    int len;    // send data    len = send(fd, ev->buff, ev->len, 0);    ev->len = 0;    EventDel(g_epollFd, ev);    if(len > 0)    {        // change to receive event        EventSet(ev, fd, RecvData, ev);        EventAdd(g_epollFd, EPOLLIN|EPOLLET, ev);    }    else    {        close(ev->fd);        printf("recv[fd=%d] error[%d]\n", fd, errno);    }}void InitListenSocket(int epollFd, short port){    int listenFd = socket(AF_INET, SOCK_STREAM, 0);    fcntl(listenFd, F_SETFL, O_NONBLOCK); // set non-blocking    printf("server listen fd=%d\n", listenFd);    EventSet(&g_Events[MAX_EVENTS], listenFd, AcceptConn, &g_Events[MAX_EVENTS]);    // add listen socket    EventAdd(epollFd, EPOLLIN|EPOLLET, &g_Events[MAX_EVENTS]);    // bind & listen    sockaddr_in sin;    bzero(&sin, sizeof(sin));    sin.sin_family = AF_INET;    sin.sin_addr.s_addr = INADDR_ANY;    sin.sin_port = htons(port);    bind(listenFd, (const sockaddr*)&sin, sizeof(sin));    listen(listenFd, 5);}int main(int argc, char **argv){    short port = 12345; // default port    if(argc == 2){        port = atoi(argv[1]);    }    // create epoll    g_epollFd = epoll_create(MAX_EVENTS);    if(g_epollFd <= 0) printf("create epoll failed.%d\n", g_epollFd);    // create & bind listen socket, and add to epoll, set non-blocking    InitListenSocket(g_epollFd, port);    // event loop    struct epoll_event events[MAX_EVENTS];    printf("server running:port[%d]\n", port);    int checkPos = 0;    while(1){        // a simple timeout check here, every time 100, better to use a mini-heap, and add timer event        long now = time(NULL);        for(int i = 0; i < 100; i++, checkPos++) // doesn't check listen fd        {            if(checkPos == MAX_EVENTS) checkPos = 0; // recycle            if(g_Events[checkPos].status != 1) continue;            long duration = now - g_Events[checkPos].last_active;            if(duration >= 60) // 60s timeout            {                close(g_Events[checkPos].fd);                printf("[fd=%d] timeout[%d--%d].\n", g_Events[checkPos].fd, g_Events[checkPos].last_active, now);                EventDel(g_epollFd, &g_Events[checkPos]);            }        }        // wait for events to happen        int fds = epoll_wait(g_epollFd, events, MAX_EVENTS, 1000);        if(fds < 0){            printf("epoll_wait error, exit\n");            break;        }        for(int i = 0; i < fds; i++){            myevent_s *ev = (struct myevent_s*)events[i].data.ptr;            if((events[i].events&EPOLLIN)&&(ev->events&EPOLLIN)) // read event            {                ev->call_back(ev->fd, events[i].events, ev->arg);            }            if((events[i].events&EPOLLOUT)&&(ev->events&EPOLLOUT)) // write event            {                ev->call_back(ev->fd, events[i].events, ev->arg);            }        }    }    // free resource    return 0;}

 

三、 异步通知

1. 定义信号处理函数
2. 设置socket的消息进程id
3. 设置socket消息
4. 信号等待和处理

例子：

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <string.h>#include <signal.h>#include <netinet/in.h>#include <arpa/inet.h>#include <sys/socket.h>#include <sys/types.h>#include <sys/ioctl.h>#define MAX_LENTH 1500#define SIG_FIFO_IO SIGRTMIN+1static char recv_buf[MAX_LENTH] = {0};int main(int argc, char *argv[]){    int sockfd, on = 1;    struct sigaction action;    sigset_t newmask, oldmask;    struct sockaddr_in addr;    memset(&addr, 0, sizeof(addr));    addr.sin_family =  AF_INET;    addr.sin_addr.s_addr = INADDR_ANY;    addr.sin_port = htons(50001);    if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {        perror("Create socket failed");        exit(-1);    }    if (bind(sockfd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {        perror("Bind socket failed");        exit(-1);    }    if (fcntl(sockfd, F_SETOWN, getpid()) == -1) {        perror("Fcntl F_SETOWN failed");        exit(-1);    }    if (fcntl(sockfd, F_SETSIG, SIG_FIFO_IO) == -1) {        perror("Fcntl F_SETSIG failed");        exit(-1);    }    if (ioctl(sockfd, FIOASYNC, &on) == -1) {        perror("Ioctl FIOASYNC failed");        exit(-1);    }    int rcvd_sig, len;    siginfo_t info;    sigemptyset(&newmask);    sigaddset(&newmask, SIG_FIFO_IO);    sigprocmask(SIG_BLOCK, &newmask, &oldmask);    while (1) {        rcvd_sig = sigwaitinfo(&newmask, &info);//siginfo中的_sigpool{si_band, si_fd},其中si_fd为socket的文件描述符值        if (rcvd_sig == -1) {            perror("sigio: sigwaitinfo");            exit(-1);        }        else {            printf("Signal %d, socket fd %d  received from socket\n",                    rcvd_sig, info.si_fd);            len = recv(sockfd, recv_buf, MAX_LENTH, MSG_DONTWAIT);            if( len>0)                puts( recv_buf);            exit(-1);        }    }    exit(0);}