diff options
Diffstat (limited to 'compiler/codeGen')
| -rw-r--r-- | compiler/codeGen/StgCmmBind.hs | 35 |
1 files changed, 4 insertions, 31 deletions
diff --git a/compiler/codeGen/StgCmmBind.hs b/compiler/codeGen/StgCmmBind.hs index 05aae0aeeb..23367926c7 100644 --- a/compiler/codeGen/StgCmmBind.hs +++ b/compiler/codeGen/StgCmmBind.hs @@ -695,44 +695,17 @@ emitUpdateFrame dflags frame lbl updatee = do ----------------------------------------------------------------------------- -- Entering a CAF -- --- When a CAF is first entered, it creates a black hole in the heap, --- and updates itself with an indirection to this new black hole. --- --- We update the CAF with an indirection to a newly-allocated black --- hole in the heap. We also set the blocking queue on the newly --- allocated black hole to be empty. --- --- Why do we make a black hole in the heap when we enter a CAF? --- --- - for a generational garbage collector, which needs a fast --- test for whether an updatee is in an old generation or not --- --- - for the parallel system, which can implement updates more --- easily if the updatee is always in the heap. (allegedly). --- --- When debugging, we maintain a separate CAF list so we can tell when --- a CAF has been garbage collected. - --- newCAF must be called before the itbl ptr is overwritten, since --- newCAF records the old itbl ptr in order to do CAF reverting --- (which Hugs needs to do in order that combined mode works right.) --- +-- See Note [CAF management] in rts/sm/Storage.c link_caf :: LocalReg -- pointer to the closure -> Bool -- True <=> updatable, False <=> single-entry -> FCode CmmExpr -- Returns amode for closure to be updated --- To update a CAF we must allocate a black hole, link the CAF onto the --- CAF list, then update the CAF to point to the fresh black hole. -- This function returns the address of the black hole, so it can be --- updated with the new value when available. The reason for all of this --- is that we only want to update dynamic heap objects, not static ones, --- so that generational GC is easier. +-- updated with the new value when available. link_caf node _is_upd = do { dflags <- getDynFlags - -- Call the RTS function newCAF to add the CAF to the CafList - -- so that the garbage collector can find them - -- This must be done *before* the info table pointer is overwritten, - -- because the old info table ptr is needed for reversion + -- Call the RTS function newCAF, returning the newly-allocated + -- blackhole indirection closure ; let newCAF_lbl = mkForeignLabel (fsLit "newCAF") Nothing ForeignLabelInExternalPackage IsFunction ; bh <- newTemp (bWord dflags) |