typedef struct _DISPATCHER_HEADER
{
     union
     {
          struct
          {
               UCHAR Type;
               union
               {
                    UCHAR Abandoned;
                    UCHAR Absolute;
                    UCHAR NpxIrql;
                    UCHAR Signalling;
               };
               union
               {
                    UCHAR Size;
                    UCHAR Hand;
               };
               union
               {
                    UCHAR Inserted;
                    UCHAR DebugActive;
                    UCHAR DpcActive;
               };
          };
          LONG Lock;
     };
     LONG SignalState;
     LIST_ENTRY WaitListHead;
} DISPATCHER_HEADER, *PDISPATCHER_HEADER;

Windows Vista Kernel Structures