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Re: [perl #75176] Symbol::delete_package does not free certain memory associated with package::ISA

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Father Chrysostomos
August 29, 2010 14:09
Re: [perl #75176] Symbol::delete_package does not free certain memory associated with package::ISA
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On Aug 22, 2010, at 5:46 PM, Father Chrysostomos wrote:

> Initially I planned to fix the isarev leaks by making appropriate adjustments to it whenever an @ISA is modified or a stash is freed. But, since stashes can be detached from the main tree of stashes ($stash = delete $::{"it::"}), they need to know whether they are still attached, so detached stashes don’t muddle up isarev and delete entries that are still needed (which would be worse than leaking).
> In the process of experimenting with that, I found that such stash manipulations already fail to update isa caches, which, too, would cause my proposed isarev changes to introduce regressions. So that’s what this patch is for.

Here is a patch that deals with a couple more ways of manipulating stashes.

I plan to work on assignment to empty stash elements next (or any stash elements that are not globs). I can do this by using PVLVs. But there are two approaches:

1. Do it just for access from Perl by adding it to pp_helem.
2. Do it for XS access as well, by modifying hv_fetch_ent instead (or hv_common, or wherever the actual code is).

Number 1 makes it too easy for XS code to make changes without triggering mro_package_moved. mro_package_moved will also have to be made public (and probably given a better name).
Number 2 is probably more reliable. perl’s internals can pass a flag to avoid the PVLVs. XS code that assumes that stash elements are never magical will be broken (code that specifically calls the _nomg forms to avoid the magic checks). Most XS code will continue to work.

So in both cases, XS code will have to be modified (if there is any that plays with stashes). But in case 2 only code that is currently potentially buggy will have to change.

I prefer number 2.

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