Re: [Sbcl-devel] [Sbcl-commits] master: Clear CTYPE-OF cache in SET-ARRAY-HEADER. (lp#1333731)

[Douglas K. <do...@go...>]

Flushing often is not a bad thing.
It's not a super important cache, and it's nasty one from a
garbage-retention perspective.

Unlike all the other cached functions whose inputs and outputs are CTYPE
subtypes, so little trees of small structs whose leaves are symbols, the
CTYPE-OF cache caches anything, but it's not using weak pointers.
(To be fair, all EQL types retains the object they point to; and PCL has a
similar problem with EQL specializers)

I suspect that I'd like to make the cache use weak pointers, or possibly
reduce the size if not using weak pointers, and make it use double-wide CAS
on x86-64 so that allocating a new cache line does not cons, *and*
implement your suggestion too. (Not in that order. The flush-1-line
function is probably the easiest change)

In terms of the other callers - most uses are only because it's the faster
thing than ADJUST-ARRAY, but logically they mean to be doing ADJUST-ARRAY
and are just cheating for a little bit of speed. (for 'stream.lisp' and
'reader.lisp' this is for certain)

Can there be made a function which only clears the cache for a
> particular array? And set-array-header is being called by other
> functions, not just adjust-array, is ctype-of-cache-clear needed for
> them as well?
>