The winfo_item Class

As described in Section 10.1.1 the winfo array variable stores the various pointer to the wait_info objects of a process. winfo is an array of winfo_item elements. wait_item is defined as follows:

class winfo_item {
   union _data { wait_info *wi; winfo_item *wii; };
   _data data;
  public:
   winfo_item() { data.wi = NULL; data.wii = NULL; }
   operator wait_info*() { return data.wi; }
   operator winfo_item*() { return data.wii; }
   winfo_item &operator=(wait_info *a) { 
      data.wi = a; return *this;
   }
   winfo_item &operator=(winfo_item *a) { 
      data.wii = a; return *this;
   }
};

Hence, a array element of type winfo_item may store a pointer to a wait_info object or a pointer to a winfo_item list. This structure is useful to deal with procedures that contain wait statements. Procedures which include wait statements will take a reference to an element of the winfo array as an argument. This element will store a pointer to a separate new winfo array which in turn contains references to all wait_info objects used within the procedure.