[Python-Dev] PEP 442: Safe object finalization

[Eli Bendersky]

Great PEP, I would really like to see this happen as it defines much saner
semantics for finalization than what we currently have. One small question
below:


 This PEP proposes to turn CI disposal into the following sequence (new
> steps are in bold):
>
> 1. Weakrefs to CI objects are cleared, and their callbacks called. At
>    this point, the objects are still safe to use.
>
> 2. **The finalizers of all CI objects are called.**
>
> 3. **The CI is traversed again to determine if it is still isolated.
>    If it is determined that at least one object in CI is now reachable
>    from outside the CI, this collection is aborted and the whole CI
>    is resurrected.  Otherwise, proceed.**
>

Not sure if my question is the same as Armin's here, but worth a try: by
saying "the CI is traversed again" do you mean the original objects from
the CI as discovered earlier, or is a new scan being done? What about a new
object entering the CI during step (2)? I.e. the original CI was A->B->A
but now one of the finalizers created some C such that B->C and C->A adding
it to the connected component?

Reading your description in (3) strictly it says: in this case the
collection is aborted. This CI will be disposed next time collection is
run. Is this correct?

Eli



>
> 4. The CI becomes a CT as the GC systematically breaks all
>    known references inside it (using the ``tp_clear`` function).
>
> 5. Nothing.  All CT objects should have been disposed of in step 4
>    (as a side-effect of clearing references); this collection is
>    finished.
>

Eli
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