typedef struct _TP_CALLBACK_ENVIRON
{
     ULONG Version;
     _TP_POOL * Pool;
     _TP_CLEANUP_GROUP * CleanupGroup;
     PVOID CleanupGroupCancelCallback;
     PVOID RaceDll;
     _ACTIVATION_CONTEXT * ActivationContext;
     PVOID FinalizationCallback;
     ULONG u;
} TP_CALLBACK_ENVIRON, *PTP_CALLBACK_ENVIRON;

Windows Vista Kernel Structures