diff options
Diffstat (limited to 'rts/sm/Scav.c')
| -rw-r--r-- | rts/sm/Scav.c | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/rts/sm/Scav.c b/rts/sm/Scav.c index 24f19c93e1..d396b9f7f6 100644 --- a/rts/sm/Scav.c +++ b/rts/sm/Scav.c @@ -1680,24 +1680,34 @@ scavenge_stack(StgPtr p, StgPtr stack_end) // the indirection into an IND_PERM, so that evacuate will // copy the indirection into the old generation instead of // discarding it. + // + // Note [upd-black-hole] + // One slight hiccup is that the THUNK_SELECTOR machinery can + // overwrite the updatee with an IND. In parallel GC, this + // could even be happening concurrently, so we can't check for + // the IND. Fortunately if we assume that blackholing is + // happening (either lazy or eager), then we can be sure that + // the updatee is never a THUNK_SELECTOR and we're ok. + // NB. this is a new invariant: blackholing is not optional. { nat type; const StgInfoTable *i; + StgClosure *updatee; - i = ((StgUpdateFrame *)p)->updatee->header.info; + updatee = ((StgUpdateFrame *)p)->updatee; + i = updatee->header.info; if (!IS_FORWARDING_PTR(i)) { - type = get_itbl(((StgUpdateFrame *)p)->updatee)->type; + type = get_itbl(updatee)->type; if (type == IND) { - ((StgUpdateFrame *)p)->updatee->header.info = - (StgInfoTable *)&stg_IND_PERM_info; + updatee->header.info = &stg_IND_PERM_info; } else if (type == IND_OLDGEN) { - ((StgUpdateFrame *)p)->updatee->header.info = - (StgInfoTable *)&stg_IND_OLDGEN_PERM_info; + updatee->header.info = &stg_IND_OLDGEN_PERM_info; } - evacuate(&((StgUpdateFrame *)p)->updatee); - p += sizeofW(StgUpdateFrame); - continue; } + evacuate(&((StgUpdateFrame *)p)->updatee); + ASSERT(GET_CLOSURE_TAG(((StgUpdateFrame *)p)->updatee) == 0); + p += sizeofW(StgUpdateFrame); + continue; } // small bitmap (< 32 entries, or 64 on a 64-bit machine) |