突破select上限的方法(windows下)

大家耳熟能詳的方法：

1.修改定義的宏

#undef FD_SETSIZE

#define FD_SETSIZE 1024

2.從boost asio中抽取的代碼

class win_fd_set_adapter : noncopyable{public:  enum { default_fd_set_size = 1024 };  win_fd_set_adapter()    : capacity_(default_fd_set_size),      max_descriptor_(invalid_socket)  {    fd_set_ = static_cast<win_fd_set*>(::operator new(          sizeof(win_fd_set) - sizeof(SOCKET)          + sizeof(SOCKET) * (capacity_)));    fd_set_->fd_count = 0;  }  ~win_fd_set_adapter()  {    ::operator delete(fd_set_);  }  void reset()  {    fd_set_->fd_count = 0;    max_descriptor_ = invalid_socket;  }  bool set(socket_type descriptor)  {    for (u_int i = 0; i < fd_set_->fd_count; ++i)      if (fd_set_->fd_array[i] == descriptor)        return true;    if (fd_set_->fd_count == capacity_)    {      u_int new_capacity = capacity_ + capacity_ / 2;      win_fd_set* new_fd_set = static_cast<win_fd_set*>(::operator new(            sizeof(win_fd_set) - sizeof(SOCKET)            + sizeof(SOCKET) * (new_capacity)));      new_fd_set->fd_count = fd_set_->fd_count;      for (u_int i = 0; i < fd_set_->fd_count; ++i)        new_fd_set->fd_array[i] = fd_set_->fd_array[i];      ::operator delete(fd_set_);      fd_set_ = new_fd_set;      capacity_ = new_capacity;    }    fd_set_->fd_array[fd_set_->fd_count++] = descriptor;    return true;  }  bool is_set(socket_type descriptor) const  {    return !!__WSAFDIsSet(descriptor,        const_cast<fd_set*>(reinterpret_cast<const fd_set*>(fd_set_)));  }  operator fd_set*()  {    return reinterpret_cast<fd_set*>(fd_set_);  }  socket_type max_descriptor() const  {    return max_descriptor_;  }private:  // This structure is defined to be compatible with the Windows API fd_set  // structure, but without being dependent on the value of FD_SETSIZE. We use  // the "struct hack" to allow the number of descriptors to be varied at  // runtime.  struct win_fd_set  {    u_int fd_count;    SOCKET fd_array[1];  };  win_fd_set* fd_set_;  u_int capacity_;  socket_type max_descriptor_;};

使用該類替代fd_set集合,FD_SET使用該類的方法set來替換,而FD_ISSET則用is_set替代,裡面的幾個資料類型自己typedef一下,缺少的標頭檔自己加下,noncopyable是boost裡面定義的禁止拷貝類(拷貝建構函式,賦值操作為private類型,建構函式和解構函式定義為protected類型)

class noncopyable  {   protected:      noncopyable() {}      ~noncopyable() {}   private:  // emphasize the following members are private      noncopyable( const noncopyable& );      const noncopyable& operator=( const noncopyable& );  };

另外提一下,windows下的FD_SETSIZE指最大可以輪詢的個數,而linux的FD_SETSIZE指的是最大檔案描述符,如果輪詢的描述符大於等於該值,可能就出問題,見man:

Executing FD_CLR() or FD_SET() with a value of fd that is negative or is equal to or larger than FD_SETSIZE will result in undefined behavior.