libevent源码剖析（一）

/*
  版本：2.1.11
  源码位置：sample/hello-world.c

  This example program provides a trivial server program that listens for TCP
  connections on port 9995.  When they arrive, it writes a short message to
  each client connection, and closes each connection once it is flushed.
  这个例子提供一个小的服务器程序：监听9995端口上的TCP连接。
  当连接请求到来，回写一个字符串，当写缓冲区刷新后立即断开。
  Where possible, it exits cleanly in response to a SIGINT (ctrl-c).
  ctrl+c发送SIGINT信号后，程序响应信号并结束。
*/


#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#ifndef _WIN32
#include <netinet/in.h>
#ifdef _XOPEN_SOURCE_EXTENDED
#include <arpa/inet.h>
#endif
#include <sys/socket.h>
#endif

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


/*
从下面的用户自定义数据来看：
    不变的数据都定义成静态类型；

*/
static const char MESSAGE[] = "Hello, World!
";

static const int PORT = 9995;

//监听器回调
static void listener_cb(struct evconnlistener *, evutil_socket_t,
    struct sockaddr *, int socklen, void *);
//写回调
static void conn_writecb(struct bufferevent *, void *);
//错误回调
static void conn_eventcb(struct bufferevent *, short, void *);
//信号事件回调
static void signal_cb(evutil_socket_t, short, void *);

int
main(int argc, char **argv)
{
    struct event_base *base;
    struct evconnlistener *listener;
    struct event *signal_event;

    struct sockaddr_in sin;
#ifdef _WIN32
    WSADATA wsa_data;
    WSAStartup(0x0201, &wsa_data);
#endif

    //1.创建event_base，用于对未决事件和激活事件的监视
    base = event_base_new();
    if (!base) {
        fprintf(stderr, "Could not initialize libevent!
");
        return 1;
    }
    //2.服务器地址
    memset(&sin, 0, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_port = htons(PORT);

    //3.创建监听器
    listener = evconnlistener_new_bind(base, listener_cb, (void *)base,
        LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE, -1,
        (struct sockaddr*)&sin,
        sizeof(sin));

    if (!listener) {
        fprintf(stderr, "Could not create a listener!
");
        return 1;
    }
    //4.创建信号事件
    signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);
    //5.将信号事件添加到调度循环
    if (!signal_event || event_add(signal_event, NULL)<0) {
        fprintf(stderr, "Could not create/add a signal event!
");
        return 1;
    }
    //6.开启调度循环，监视未决事件
    event_base_dispatch(base);
    //7.释放资源
    evconnlistener_free(listener);
    event_free(signal_event);
    event_base_free(base);

    printf("done
");
    return 0;
}

static void
listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
    struct sockaddr *sa, int socklen, void *user_data)
{
    struct event_base *base = user_data;
    struct bufferevent *bev;

    bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
    if (!bev) {
        fprintf(stderr, "Error constructing bufferevent!");
        event_base_loopbreak(base);
        return;
    }
    bufferevent_setcb(bev, NULL, conn_writecb, conn_eventcb, NULL);
    bufferevent_enable(bev, EV_WRITE);
    bufferevent_disable(bev, EV_READ);

    bufferevent_write(bev, MESSAGE, strlen(MESSAGE));
}

static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
    struct evbuffer *output = bufferevent_get_output(bev);
    if (evbuffer_get_length(output) == 0) {
        printf("flushed answer
");
        bufferevent_free(bev);
    }
}

static void
conn_eventcb(struct bufferevent *bev, short events, void *user_data)
{
    if (events & BEV_EVENT_EOF) {
        printf("Connection closed.
");
    } else if (events & BEV_EVENT_ERROR) {
        printf("Got an error on the connection: %s
",
            strerror(errno));/*XXX win32*/
    }
    /* None of the other events can happen here, since we haven't enabled
     * timeouts */
    bufferevent_free(bev);
}

static void
signal_cb(evutil_socket_t sig, short events, void *user_data)
{
    struct event_base *base = user_data;
    struct timeval delay = { 2, 0 };

    printf("Caught an interrupt signal; exiting cleanly in two seconds.
");

    event_base_loopexit(base, &delay);
}