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perf: generation-guarded cache for multimethod hierarchy dispatch

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The expensive multimethod path is the hierarchy fallback: when a dispatch value
isn't a direct method key, mm-fn walks every key with isa? (derive-based
dispatch). That resolution is now cached per dispatch value on the multimethod
var (:jolt/dispatch-cache), cleared in place by defmethod/prefer-method/
remove-method/remove-all-methods so a redefinition can't be served stale. Direct
(get methods dv) hits stay uncached — already a single lookup.

Test cases added to dispatch-cache-test (compile, interpret, aot-core off):
hierarchy hit is cached, a newly-added specific method is seen, removal re-exposes
the fallback. Conformance 218/218; full suite green.
This commit is contained in:
Yogthos 2026-06-06 18:36:11 -04:00
parent e02ccab4c0
commit c975f5d1c3
2 changed files with 54 additions and 17 deletions
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18
test/integration/dispatch-cache-test.janet
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@ -28,6 +28,24 @@
(check (string mode " other class") (eval-string ctx "(m \"hi\")") "s:hi")
(check (string mode " number after other-class extend") (eval-string ctx "(m 3)") 103))
# Multimethod hierarchy-fallback cache (jolt-g8w): the isa? walk result for a
# dispatch value is cached; defmethod/remove-method must invalidate it.
(each mode [{:compile? true} {} {:aot-core? false}]
(def ctx (init mode))
(eval-string ctx "(derive ::circle ::shape)")
(eval-string ctx "(derive ::square ::shape)")
(eval-string ctx "(defmulti area identity)")
(eval-string ctx "(defmethod area ::shape [_] :generic)")
(check (string mode " mm hierarchy") (eval-string ctx "(area ::circle)") :generic)
(check (string mode " mm cache hit") (eval-string ctx "(area ::circle)") :generic)
# adding a more specific method must invalidate the cached hierarchy result
(eval-string ctx "(defmethod area ::circle [_] :specific)")
(check (string mode " mm sees new method") (eval-string ctx "(area ::circle)") :specific)
(check (string mode " mm other still hierarchy") (eval-string ctx "(area ::square)") :generic)
# removing it must re-expose the hierarchy fallback
(eval-string ctx "(remove-method area ::circle)")
(check (string mode " mm sees removal") (eval-string ctx "(area ::circle)") :generic))
(if (pos? failures)
(do (printf "dispatch-cache: %d failure(s)" failures) (os/exit 1))
(print "dispatch-cache: all cases passed (compile, interpret, aot-core off)"))