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Soft/WeakReference: real GC eviction via Chez weak pairs + guardians

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Replace the strong-ref stub with genuine reclamation. The referent is held
through a weak-cons, so Chez's generational collector reclaims it once it is
otherwise unreachable (the pair's car becomes the bwp object, and .get returns
nil). A guardian registered on the referent makes the reference itself available
the instant its referent is collected, which ReferenceQueue.poll surfaces as
enqueued — the same hook clojure.core.cache's clear-soft-cache! drains.

Chez has no softer-than-weak reference, so a SoftReference clears on
unreachability rather than under memory pressure: a SoftCache evicts more eagerly
than the JVM's but is now real GC eviction, not an unbounded strong cache.
WeakReference gets the same (faithful) semantics. Added System/gc -> a full
collect so callers (and the queue) can force the cycle.

core.cache stays 1314/0/0 (its test values are immortal literals). Corpus row for
System/gc; make test + shakesmoke green.
This commit is contained in:
Yogthos 2026-06-25 11:32:32 -04:00
parent e955b2072a
commit 80b2dfa9f9
3 changed files with 41 additions and 25 deletions
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test/chez/corpus.edn
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@ -14,6 +14,7 @@
{:suite "interop / Thread" :label "start + join runs the thunk" :expected "7" :actual "(let [a (atom 0) t (Thread. (fn [] (reset! a 7)))] (.start t) (.join t) (deref a))"}
{:suite "interop / CountDownLatch" :label "countDown to zero, await returns" :expected "0" :actual "(let [l (java.util.concurrent.CountDownLatch. 1)] (.countDown l) (.await l) (.getCount l))"}
{:suite "interop / SoftReference" :label "get returns the referent" :expected ":v" :actual "(.get (java.lang.ref.SoftReference. :v))"}
{:suite "interop / System.gc" :label "gc runs and returns" :expected "42" :actual "(do (System/gc) 42)"}
{:suite "interop / ConcurrentHashMap" :label "put + get/count/contains?" :expected "[1 1 true]" :actual "(let [m (java.util.concurrent.ConcurrentHashMap.)] (.put m :a 1) [(get m :a) (count m) (contains? m :a)])"}
{:suite "interop / Class.forName" :label "unknown class throws ClassNotFoundException" :expected ":nf" :actual "(try (Class/forName \"no.such.Klass\") (catch ClassNotFoundException _ :nf))"}
{:suite "interop / Class.forName" :label "known class resolves" :expected "\"java.lang.String\"" :actual "(.getName (Class/forName \"java.lang.String\"))"}