转自：

 

 

 

只要接触过c/c++网路编程人都可能会知道select io 模式，网络书籍都说 fd_set {int num; SOCKET arr[64]} 有所限制，因为数组的长度只有64，那么超过64你就不能放，要么你就是用多线程分别实用select.。

一些书籍通过改定义宏 使数组的长度变长，但也不实用，不能动态的变化，我总不能定一个非常的长的长度，毕竟是在栈上。

   我就在想那么select完全只能在客户端使用，而且套接字还不能超过64。那这不就是一个软肋吗？？一直对这个有一个迷惑。。。。。

 

   后来，自己看到了libevent的源代码发现他也用的是select。。看别人说这个库，轻轻松松处理上万个套接字，我就在想select不是有限制吗？？他是怎么做到。。。。。。

看了源代码，我明白了。他只是用对上存放SOCKET的句柄。。我们看一下他的新定义结构体。

 

struct win_fd_set {

u_int fd_count;

SOCKET fd_array[1];

};

 

这个就是新定义结构体，跟原来稍微有点变化只是把64改为1，有些同学可能见多很多这样的写法，这种写法我也在一些项目使用了。这种写法可以fd_array动态变化。

win_fd_set * Set = (win_fd_set*)malloc(sizeof(win_fd_set) + sizoef(SCOEKT) * 10);

Set->fd_array 可以放11 个 SOCKET，因为我的内存大小足够放11个SOCKET。

请记住内存是没有数据格式，只要足够大小，随便你怎么放。数据格式只是方便我们管理和处理数据而已。

这样就解决64个大小限制。。我其实一直很好奇为什么中国书籍都是一样的，libevent已经出来好久了，但也没有看到有人说这一点，可能是高手们都不屑。

现在渐渐喜欢看开源的代码，不喜欢看书籍了，喜欢在代码中学习他们是怎么组织一个好项目。

有时候感慨：

高手用c 写着漂亮的c++代码，而我等菜鸟却用c++ 写丑陋的c代码。。

 

我顺便把他整个定义结构和函数给大家贴出来，免大家还要自己去下libevent，不过推荐没有看过libevent同学，可以稍微看一下。

volatile double SIGFPE_REQ = 0.0f;  struct idx_info {     int read_pos_plus1;     int write_pos_plus1; };  struct win32op {     unsigned num_fds_in_fd_sets;     int resize_out_sets;     struct win_fd_set *readset_in;     struct win_fd_set *writeset_in;     struct win_fd_set *readset_out;     struct win_fd_set *writeset_out;     struct win_fd_set *exset_out;     unsigned signals_are_broken : 1; };  static void *win32_init(struct event_base *); static int win32_add(struct event_base *, evutil_socket_t, short old, short events, void *_idx); static int win32_del(struct event_base *, evutil_socket_t, short old, short events, void *_idx); static int win32_dispatch(struct event_base *base, struct timeval *); static void win32_dealloc(struct event_base *);  struct eventop win32ops = {     "win32",     win32_init,     win32_add,     win32_del,     win32_dispatch,     win32_dealloc,     0, /* doesn't need reinit */     0, /* No features supported. */     sizeof(struct idx_info), };  #define FD_SET_ALLOC_SIZE(n) ((sizeof(struct win_fd_set) + ((n)-1)*sizeof(SOCKET)))  static int grow_fd_sets(struct win32op *op, unsigned new_num_fds) {     size_t size;      EVUTIL_ASSERT(new_num_fds >= op->readset_in->fd_count &&            new_num_fds >= op->writeset_in->fd_count);     EVUTIL_ASSERT(new_num_fds >= 1);      size = FD_SET_ALLOC_SIZE(new_num_fds);     if (!(op->readset_in = mm_realloc(op->readset_in, size)))         return (-1);     if (!(op->writeset_in = mm_realloc(op->writeset_in, size)))         return (-1);     op->resize_out_sets = 1;     op->num_fds_in_fd_sets = new_num_fds;     return (0); }  static int do_fd_set(struct win32op *op, struct idx_info *ent, evutil_socket_t s, int read) {     struct win_fd_set *set = read ? op->readset_in : op->writeset_in;     if (read) {         if (ent->read_pos_plus1 > 0)             return (0);     } else {         if (ent->write_pos_plus1 > 0)             return (0);     }     if (set->fd_count == op->num_fds_in_fd_sets) {         if (grow_fd_sets(op, op->num_fds_in_fd_sets*2))             return (-1);         /* set pointer will have changed and needs reiniting! */         set = read ? op->readset_in : op->writeset_in;     }     set->fd_array[set->fd_count] = s;     if (read)         ent->read_pos_plus1 = set->fd_count+1;     else         ent->write_pos_plus1 = set->fd_count+1;     return (set->fd_count++); }  static int do_fd_clear(struct event_base *base,             struct win32op *op, struct idx_info *ent, int read) {     int i;     struct win_fd_set *set = read ? op->readset_in : op->writeset_in;     if (read) {         i = ent->read_pos_plus1 - 1;         ent->read_pos_plus1 = 0;     } else {         i = ent->write_pos_plus1 - 1;         ent->write_pos_plus1 = 0;     }     if (i < 0)         return (0);     if (--set->fd_count != (unsigned)i) {         struct idx_info *ent2;         SOCKET s2;         s2 = set->fd_array[i] = set->fd_array[set->fd_count];          ent2 = evmap_io_get_fdinfo(&base->io, s2);          if (!ent2) /* This indicates a bug. */             return (0);         if (read)             ent2->read_pos_plus1 = i+1;         else             ent2->write_pos_plus1 = i+1;     }     return (0); }  #define NEVENT 32 void * win32_init(struct event_base *_base) {     struct win32op *winop;     size_t size;     if (!(winop = mm_calloc(1, sizeof(struct win32op))))         return NULL;     winop->num_fds_in_fd_sets = NEVENT;     size = FD_SET_ALLOC_SIZE(NEVENT);     if (!(winop->readset_in = mm_malloc(size)))         goto err;     if (!(winop->writeset_in = mm_malloc(size)))         goto err;     if (!(winop->readset_out = mm_malloc(size)))         goto err;     if (!(winop->writeset_out = mm_malloc(size)))         goto err;     if (!(winop->exset_out = mm_malloc(size)))         goto err;     winop->readset_in->fd_count = winop->writeset_in->fd_count = 0;     winop->readset_out->fd_count = winop->writeset_out->fd_count         = winop->exset_out->fd_count = 0;      if (evsig_init(_base) < 0)         winop->signals_are_broken = 1;      return (winop);  err:     XFREE(winop->readset_in);     XFREE(winop->writeset_in);     XFREE(winop->readset_out);     XFREE(winop->writeset_out);     XFREE(winop->exset_out);     XFREE(winop);     return (NULL); }  int win32_add(struct event_base *base, evutil_socket_t fd,              short old, short events, void *_idx) {     struct win32op *win32op = base->evbase;     struct idx_info *idx = _idx;      if ((events & EV_SIGNAL) && win32op->signals_are_broken)         return (-1);      if (!(events & (EV_READ|EV_WRITE)))         return (0);      event_debug(("%s: adding event for %d", __func__, (int)fd));     if (events & EV_READ) {         if (do_fd_set(win32op, idx, fd, 1)<0)             return (-1);     }     if (events & EV_WRITE) {         if (do_fd_set(win32op, idx, fd, 0)<0)             return (-1);     }     return (0); }  int win32_del(struct event_base *base, evutil_socket_t fd, short old, short events,           void *_idx) {     struct win32op *win32op = base->evbase;     struct idx_info *idx = _idx;      event_debug(("%s: Removing event for "EV_SOCK_FMT,         __func__, EV_SOCK_ARG(fd)));     if (events & EV_READ)         do_fd_clear(base, win32op, idx, 1);     if (events & EV_WRITE)         do_fd_clear(base, win32op, idx, 0);      return 0; }  static void fd_set_copy(struct win_fd_set *out, const struct win_fd_set *in) {     out->fd_count = in->fd_count;     memcpy(out->fd_array, in->fd_array, in->fd_count * (sizeof(SOCKET))); }  /*   static void dump_fd_set(struct win_fd_set *s)   {   unsigned int i;   printf("[ ");   for(i=0;i
      
       fd_count;++i)   printf("%d ",(int)s->fd_array[i]);   printf("]\n");   } */  int win32_dispatch(struct event_base *base, struct timeval *tv) {     struct win32op *win32op = base->evbase;     int res = 0;     unsigned j, i;     int fd_count;     SOCKET s;      if (win32op->resize_out_sets) {         size_t size = FD_SET_ALLOC_SIZE(win32op->num_fds_in_fd_sets);         if (!(win32op->readset_out = mm_realloc(win32op->readset_out, size)))             return (-1);         if (!(win32op->exset_out = mm_realloc(win32op->exset_out, size)))             return (-1);         if (!(win32op->writeset_out = mm_realloc(win32op->writeset_out, size)))             return (-1);         win32op->resize_out_sets = 0;     }      fd_set_copy(win32op->readset_out, win32op->readset_in);     fd_set_copy(win32op->exset_out, win32op->writeset_in);     fd_set_copy(win32op->writeset_out, win32op->writeset_in);      fd_count =         (win32op->readset_out->fd_count > win32op->writeset_out->fd_count) ?         win32op->readset_out->fd_count : win32op->writeset_out->fd_count;      if (!fd_count) {         long msec = tv ? evutil_tv_to_msec(tv) : LONG_MAX;         /* Sleep's DWORD argument is unsigned long */         if (msec < 0)             msec = LONG_MAX;         /* Windows doesn't like you to call select() with no sockets */         Sleep(msec);         return (0);     }      EVBASE_RELEASE_LOCK(base, th_base_lock);      res = select(fd_count,              (struct fd_set*)win32op->readset_out,              (struct fd_set*)win32op->writeset_out,              (struct fd_set*)win32op->exset_out, tv);      EVBASE_ACQUIRE_LOCK(base, th_base_lock);      event_debug(("%s: select returned %d", __func__, res));      if (res <= 0) {         return res;     }      if (win32op->readset_out->fd_count) {         i = rand() % win32op->readset_out->fd_count;         for (j=0; j
       
        readset_out->fd_count; ++j) {             if (++i >= win32op->readset_out->fd_count)                 i = 0;             s = win32op->readset_out->fd_array[i];             evmap_io_active(base, s, EV_READ);         }     }     if (win32op->exset_out->fd_count) {         i = rand() % win32op->exset_out->fd_count;         for (j=0; j
        
         exset_out->fd_count; ++j) {             if (++i >= win32op->exset_out->fd_count)                 i = 0;             s = win32op->exset_out->fd_array[i];             evmap_io_active(base, s, EV_WRITE);         }     }     if (win32op->writeset_out->fd_count) {         SOCKET s;         i = rand() % win32op->writeset_out->fd_count;         for (j=0; j
         
          writeset_out->fd_count; ++j) {             if (++i >= win32op->writeset_out->fd_count)                 i = 0;             s = win32op->writeset_out->fd_array[i];             evmap_io_active(base, s, EV_WRITE);         }     }     return (0); }  void win32_dealloc(struct event_base *_base) {     struct win32op *win32op = _base->evbase;      evsig_dealloc(_base);     if (win32op->readset_in)         mm_free(win32op->readset_in);     if (win32op->writeset_in)         mm_free(win32op->writeset_in);     if (win32op->readset_out)         mm_free(win32op->readset_out);     if (win32op->writeset_out)         mm_free(win32op->writeset_out);     if (win32op->exset_out)         mm_free(win32op->exset_out);     /* XXXXX free the tree. */      memset(win32op, 0, sizeof(win32op));     mm_free(win32op); }