libevent：为啥 evutil_make_socket_nonblocking 在他们的示例中调用了两次

Posted 2023-02-16

【中文标题】libevent：为啥 evutil_make_socket_nonblocking 在他们的示例中调用了两次

【英文标题】：libevent: why evutil_make_socket_nonblocking called twice in their examplelibevent：为什么 evutil_make_socket_nonblocking 在他们的示例中调用了两次

【发布时间】：2014-06-25 21:14:54

【问题描述】：

我正在查看 this page 上的 LibEvent 示例 - 为什么在该示例中 evutil_make_socket_nonblocking（使套接字非阻塞）函数被调用两次？

她的代码（我只是从 LibEvent 页面复制的）：

/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
/* For fcntl */
#include <fcntl.h>

#include <event2/event.h>
#include <event2/buffer.h>
#include <event2/bufferevent.h>

#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>

#define MAX_LINE 16384

void do_read(evutil_socket_t fd, short events, void *arg);
void do_write(evutil_socket_t fd, short events, void *arg);

char
rot13_char(char c)

    /* We don't want to use isalpha here; setting the locale would change
     * which characters are considered alphabetical. */
    if ((c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M'))
        return c + 13;
    else if ((c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z'))
        return c - 13;
    else
        return c;


void
readcb(struct bufferevent *bev, void *ctx)

    struct evbuffer *input, *output;
    char *line;
    size_t n;
    int i;
    input = bufferevent_get_input(bev);
    output = bufferevent_get_output(bev);

    while ((line = evbuffer_readln(input, &n, EVBUFFER_EOL_LF))) 
        for (i = 0; i < n; ++i)
            line[i] = rot13_char(line[i]);
        evbuffer_add(output, line, n);
        evbuffer_add(output, "\n", 1);
        free(line);
    

    if (evbuffer_get_length(input) >= MAX_LINE) 
        /* Too long; just process what there is and go on so that the buffer
         * doesn't grow infinitely long. */
        char buf[1024];
        while (evbuffer_get_length(input)) 
            int n = evbuffer_remove(input, buf, sizeof(buf));
            for (i = 0; i < n; ++i)
                buf[i] = rot13_char(buf[i]);
            evbuffer_add(output, buf, n);
        
        evbuffer_add(output, "\n", 1);
    


void
errorcb(struct bufferevent *bev, short error, void *ctx)

    if (error & BEV_EVENT_EOF) 
        /* connection has been closed, do any clean up here */
        /* ... */
     else if (error & BEV_EVENT_ERROR) 
        /* check errno to see what error occurred */
        /* ... */
     else if (error & BEV_EVENT_TIMEOUT) 
        /* must be a timeout event handle, handle it */
        /* ... */
    
    bufferevent_free(bev);


void
do_accept(evutil_socket_t listener, short event, void *arg)

    struct event_base *base = arg;
    struct sockaddr_storage ss;
    socklen_t slen = sizeof(ss);
    int fd = accept(listener, (struct sockaddr*)&ss, &slen);
    if (fd < 0) 
        perror("accept");
     else if (fd > FD_SETSIZE) 
        close(fd);
     else 
        struct bufferevent *bev;
        evutil_make_socket_nonblocking(fd);
        bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
        bufferevent_setcb(bev, readcb, NULL, errorcb, NULL);
        bufferevent_setwatermark(bev, EV_READ, 0, MAX_LINE);
        bufferevent_enable(bev, EV_READ|EV_WRITE);
    


void
run(void)

    evutil_socket_t listener;
    struct sockaddr_in sin;
    struct event_base *base;
    struct event *listener_event;

    base = event_base_new();
    if (!base)
        return; /*XXXerr*/

    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(40713);

    listener = socket(AF_INET, SOCK_STREAM, 0);
    evutil_make_socket_nonblocking(listener);

#ifndef WIN32
    
        int one = 1;
        setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
    
#endif

    if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) 
        perror("bind");
        return;
    

    if (listen(listener, 16)<0) 
        perror("listen");
        return;
    

    listener_event = event_new(base, listener, EV_READ|EV_PERSIST, do_accept, (void*)base);
    /*XXX check it */
    event_add(listener_event, NULL);

    event_base_dispatch(base);


int
main(int c, char **v)

    setvbuf(stdout, NULL, _IONBF, 0);

    run();
    return 0;

【参考方案1】：

监听套接字调用一次，每个接受的套接字调用一次。