Benjamin Goldberg <[EMAIL PROTECTED]> wrote:
> I'd like to reiterate (and clarify) my idea, of a hybrid scheme
> combining refcounting and DoD.
I'll try to translate this to parrot speak. I hope that I fully
understand your scheme, but lets see.
> All values needing timely destruction would inherit from a class
> RefCounted.
All such variables?! ... have a special vtable and additionally a
refcount, where the ...
> All operations on a variable or variables having the "is refcounted"
> trait result in opcodes to call the refcount(inc|dec) method(s) of the
> values in those variables.
... get_val and the set_val part of the value access does inc|dec the
refcount:
if (--PTimer->refcount == 0)
if (PObj_is_referenced(PTimer))
interpreter->need_lazy_dod = 1
else
VTABLE_destroy( .. PTimer);
> Under normal circumstances, when a refcounted value's refcount goes
> to zero, it self destructs^W^W cleans itself up.
> To avoid premature cleanup, any time that the contents of a
> refcounted variable is assigned to a non-refcounted variable, an opcode
> to set a "reachable by non-refcounted variable" flag on the value
> precedes the assignment. If a refcounted values's refcount goes to
> zero, and it has this flag set, it does NOT self-destruct[*].
set_is_referenced PTimer := PObj_is_referenced_SET(PTimer)
set PAgggregate[key], PTimer
> A global counter keeps track of how many values have a refcount of zero
> and have this flag set.
IMHO no counter just a flag, but doesn't matter now.
> From here, we are in a similar situation as other proposals -- for the
> timeliest possible destruction, then on every single scope exit, we
> check if this global counter is nonzero, and if so, do a DoD run.
lazysweep # as currently
> During the course of a DoD run, when we look for what PMCs are reachable,
> we keep track of what each thing was reachable *from*.
> If a PMC was found to be reachable through a non-refcounted variable,
> then we set a flag saying so. At the end of DoD, every reachable refcounted
> value which has the first flag set, but this other flag not set, gets it's
> first flag cleared.
I think I don't understand the "first & other flag".
If a PTimer is e.g. inside an aggregate (i.e. reachable through
non-refcounted) the live_FLAG of the PTimer gets set and it will not get
destroyed. If during the DOD run the PTimer is not referenced it will
have the live_FLAG cleared and will be destroyed.
If there are any objects with a refcount live after a DOD run, we set
again the interpreter->need_lazy_dod flag.
leo
