SGEN_FL_BUSY
(((sgen_state_t *)(stp))->sgen_flags |= SGEN_FL_BUSY)
(((sgen_state_t *)(stp))->sgen_flags &= ~SGEN_FL_BUSY)
((((sgen_state_t *)(stp))->sgen_flags & SGEN_FL_BUSY) == SGEN_FL_BUSY)