redhat enterprise 5 下的boost::asio 庫應用（4）

libev的demo上篇也說到了，那麼epoll到底是如何工作的呢，為了更好的接觸到底層，我們直接用epoll的API來設計一個echoserver

client的code和上篇一樣

echoserver.cpp 如下

#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 500   struct 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 event   void 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 epoll   void 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 epoll   void 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 fd   void RecvData(int fd, int events, void *arg);  void SendData(int fd, int events, void *arg);  // accept new connections from clients   void 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 data   void 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] = '\0';          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 data   void 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;  } 

和windows下的iocp的原理很形似，都是event通知，用回呼函數。

那下篇我們來具體分析下，各個API和call_back的關係。