反应器（Reactor）和主动器（Proactor）

　　网络方面用的比较多的库是libevent和boost.asio，两者都是跨平台的。其中libevent是基于Reactor实现的，而boost.asio是基于Proactor实现的。

1. 反应器（Reactor）

　　Reactor一般是应用程序先注册响应的事件处理器，然后启动Reactor的事件循环，不断的检查是否有就绪的IO事件，当有就绪IO事件发生时，反应器的事件循环就会调用事先注册好的事件处理器。下面代码是libevent的一个简单应用代码及就绪的IO事件发生时的堆栈图，其中就绪IO事件可以使用网络调试助手，连接本机之后即可产生。

#include "stdafx.h"#include <get='_blank'>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>static const char MESSAGE[] = "Hello, World!\n";static const int PORT = 9995;static void listener_cb(struct evconnlistener *, evutil_socket_t,  struct sockaddr *, int socklen, void *);static void conn_writecb(struct bufferevent *, void *);static void conn_eventcb(struct bufferevent *, short, void *);static void signal_cb(evutil_socket_t, short, void *);intmain(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  base = event_base_new();  if (!base) {    fprintf(stderr, "Could not initialize libevent!\n");    return 1;  }  memset(&sin, 0, sizeof(sin));  sin.sin_family = AF_.NET;  sin.sin_port = htons(PORT);  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!\n");    return 1;  }  signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);  if (!signal_event || event_add(signal_event, NULL)<0) {    fprintf(stderr, "Could not create/add a signal event!\n");    return 1;  }  event_base_dispatch(base);  evconnlistener_free(listener);  event_free(signal_event);  event_base_free(base);  printf("done\n");  return 0;}static voidlistener_cb(struct evconnlistener *listener, evutil_socket_t fd,  struct sockaddr *sa, int socklen, void *user_data){  struct event_base *base = (event_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 voidconn_writecb(struct bufferevent *bev, void *user_data){  struct evbuffer *output = bufferevent_get_output(bev);  if (evbuffer_get_length(output) == 0) {    printf("flushed answer\n");    bufferevent_free(bev);  }}static voidconn_eventcb(struct bufferevent *bev, short events, void *user_data){  if (events & BEV_EVENT_EOF) {    printf("Connection closed.\n");  } else if (events & BEV_EVENT_ERROR) {    printf("Got an error on the connection: %s\n",      strerror(errno));/*XXX win32*/  }  /* None of the other events can happen here, since we haven't enabled   * timeouts */  bufferevent_free(bev);}static voidsignal_cb(evutil_socket_t sig, short events, void *user_data){  struct event_base *base = (event_base *)user_data;  struct timeval delay = { 2, 0 };  printf("Caught an interrupt signal; exiting cleanly in two seconds.\n");  event_base_loopexit(base, &delay);}

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原标题：反应器（Reactor）和主动器（Proactor）

关键词：react