typedef struct _EX_PUSH_LOCK
{
     union
     {
          ULONG Locked: 1;
          ULONG Waiting: 1;
          ULONG Waking: 1;
          ULONG MultipleShared: 1;
          ULONG Shared: 28;
          ULONG Value;
          PVOID Ptr;
     };
} EX_PUSH_LOCK, *PEX_PUSH_LOCK;

Windows Vista Kernel Structures