GNU bug report logs - #36447
27.0.50; New "Unknown keyword" errors

Previous Next

Full log

View this message in rfc822 format

From: Pip Cet <pipcet <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: michael_heerdegen <at> web.de, 36447 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>, npostavs <at> gmail.com
Subject: bug#36447: 27.0.50; New "Unknown keyword" errors
Date: Fri, 5 Jul 2019 13:41:41 +0000

On Fri, Jul 5, 2019 at 12:33 PM Eli Zaretskii <eliz <at> gnu.org> wrote:
> Thanks for the explanations.  I'm CC'ing Stefan who knows much more
> about this than I do.

Thank you.

> > The reasons are this: when a hash table is purecopied, its ->next
> > vector is purecopied, which merges it with another, similar, hash
> > table's ->next vector if purify-flag is a (third) hash table. The
> > vectors are compared using `equal', but the pure copies are actually
> > `eq'.
>
> A naïve question: wouldn't the problem go away if we modified purecopy
> not to do the above, i.e. not to merge the next vector of a hash table
> with that of another?

I thought about that, but it's a bit complicated: either we'd keep the
->next vector impure (and make a copy of it), or we would have to add
a "don't hash-cons" argument to purecopy(), which kind of defeats the
purpose.

> > The (disappointingly trivial) fix:
> > call copy-sequence on h->next before rehashing the table.
>
> Rehashing is not only done during dumping, right?

As far as I can tell, it's only done when first accessing a dumped
hash table, but I might be wrong. (In any case, it seems
`hash-table-count' then returns a negative value for the hash table,
which seems problematic to me.)

> So the fix you
> propose also makes rehashing slightly less efficient.  Is that
> necessary, i.e. are you saying that the bug is in rehashing, not in
> purecopy?

Again, I may be wrong, since we're using the sign of h->count to
indicate whether a hash table needs rehashing and that's hard to grep
for, but I think this only affects rehashing after dump, not rehashing
when resizing a hash table. It's certainly not called very often, and
not for very large hash tables.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.