Boost: ASIO library application in RedHat Enterprise 5 (4)

As mentioned in the libev demo, how does epoll work? to better reach the underlying layer, we use epoll APIs to design an echoserver.

The client code is the same as the previous one.

Echoserver. cpp is as follows:

#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;  } 

Similar to the principle of iocp in windows, they are Event Notifications and Use callback functions.

Next, let's analyze the relationship between each API and call_back.