c - epoll(EPOLLET)取决于读取字节数？

Question

我在边缘触发模式下使用epoll。为了避免饥饿，代码从一个套接字一次读取 MAX_FREAD_LENGTH 字节。随后组装片段直至 EOL 发生。我注意到当 MAX_FREAD_LENGTH 很小时，epoll 会卡住。我认为它应该适用于任何大小的读取 block 。它在 512 字节下运行良好，但有时会挂起(意味着没有 EPOLLIN 事件)。如果我增加 MAX_FREAD_LENGTH 它会变得更加稳定。我该如何解决这个问题？

非常感谢您考虑我的问题!

EPOLL initialize

int res;
epFd = epoll_create(EPOLL_SIZE);
event.data.fd = serverFd;
event.events = EPOLLIN|EPOLLET;
res=epoll_ctl(epFd, EPOLL_CTL_ADD, serverFd, &event);
if (res == -1){
  perror ("epoll_ctl error: ");
  return EH_ERROR;
}
events = calloc (MAX_EVENTS, sizeof event);

register net event:

while (TRUE){
  int nfds;
  do{
    nfds = epoll_wait(epFd, events, MAX_EVENTS, -1);
  } while (nfds < 0 && errno == EINTR);

  int i = 0;
  for (;i<nfds;i++){
    if ( (events[i].data.fd == serverFd) && (events[i].events & EPOLLIN)){
      if ((clientFd = accept(serverFd,(struct sockaddr *) &clientAddr, &clientLen)) < 0){
        char log[255];
        sprintf(log,"dispatch_net_event: Socket accept failed: %s",strerror(errno));
        logger->log(LOGG_ERROR,log);
      }
      if(newclient(clientFd)!=EH_ERROR){
        /* client created */
        setnonblocking(fd,NONBLOCKING);
        event.data.fd = clientFd;
        event.events = EPOLLIN |EPOLLET;
        if(epoll_ctl(epFd, EPOLL_CTL_ADD, fd, &event)<0){
          fprintf(stderr,"Epoll insertion error (fd=%d): ",clientFd);
          return EH_ERROR;             
        }    
        continue;
      }
      else{
        logger->log(LOGG_ERROR,"Client creation error");
        continue;
      }
    }
    else{
     dispatch_event(events[i].data.fd,NET_EVENT);
    }
  }
}

handle a net event

#define SMTP_MAX_LINE_LENGTH MAX_FREAD_LENGTH
ssize_t count;
char buf[SMTP_MAX_LINE_LENGTH];

memset(buf,'\0', SMTP_MAX_LINE_LENGTH);
count = read (fd, buf,MAX_FREAD_LENGTH );

if (count==-1){
  if (errno == EAGAIN)
    return KEEP_IT;
  else if (errno == EWOULDBLOCK)
    return KEEP_IT;
  else{
    char log[255];
    sprintf(log,"handle_net_event: Read error: %s",strerror(errno));
    logger->log(LOGG_ERROR,log);
  }
}
else{   /* count > 0 there are data in the buffer */
  /* assemble possible partial lines, TRUE if line is whole (end with \r\n)*/
  whole=assemble_line(count,client,&buf[0]);
}
 /* process the line */

EDIT:

我忘了提及，epoll 与其他部分相比在单独的线程中运行

Answer 1

我认为您错误地使用了 EPOLLET。尝试不使用 EPOLLET(即使用电平触发模式)，看看是否有效。如果是这样，则意味着您的根本问题是您没有执行边沿触发模式所要求的操作，即继续从任何就绪描述符中读取，直到获得 EAGAIN。