Chez concurrency pt.1: real OS-thread futures + blocking promises (shared heap)

future/future-call run the body on a native thread (fork-thread) over the SAME
heap — JVM semantics, not Janet's isolated-heap snapshot. deref blocks on a
mutex+condition latch; timed (deref f ms val) uses an absolute deadline.
promise is a real blocking promise (deref parks until deliver), replacing the
Janet non-blocking atom shim. future?/future-done?/future-cancelled?/future-cancel
/realized? are native (the overlay versions read Janet map keys); re-asserted in
post-prelude over the overlay. pmap/pcalls/pvalues (overlay, over future) light
up for free.

Thread-safety this forces:
- atoms get a per-atom mutex; swap!/swap-vals! are a JVM-style CAS loop (f runs
  outside the lock, so a watch/validator can deref the same atom); reset!/
  compare-and-set! are atomic.
- the dynamic binding stack becomes a Chez thread-parameter, so each future/thread
  has its own; Chez inherits it at fork, giving binding conveyance (the shim also
  installs an explicit snapshot).
- Thread/sleep really sleeps now (a worker sleeping doesn't block the parent).

Re-minted the seed: future-call now resolves at compile time, so pmap compiles to
a var-deref instead of the host-static-call fallback that crashed. image.ss
unchanged.

Corpus: the 2 snapshot cases now match the JVM (shared) not Janet (isolated) —
allowlisted on both Chez gates; the two racy future-cancel cases allowlisted;
"promise undelivered" (blocks on JVM/Chez, profile :bucket :timeout) skipped like
:throws. Zero-Janet corpus 2544 -> 2569, 0 new divergences, floor raised. Full
Janet gate + JVM cert green.

jolt-byjr

host/chez/atoms.ss

@@ -16,16 +16,21 @@
 ;; Janet table, which a Chez atom record is not — so the peripheral ops + the
 ;; notify/validate behaviour live natively here, and post-prelude.ss re-asserts
 ;; them over the overlay's def-var! (jolt-mn9o).
+;; `lock` (jolt-byjr) is a per-atom mutex guarding the read-modify-write critical
+;; sections, so swap!/reset!/compare-and-set! are atomic under real OS threads
+;; (futures/go blocks share the heap on Chez). The user fn in swap! runs OUTSIDE
+;; the lock (a CAS retry loop, like the JVM) so it never deadlocks on re-entrant
+;; access and a watch/validator can deref the same atom.
 (define-record-type jolt-atom
-  (fields (mutable val) (mutable watches) (mutable validator))
-  (nongenerative jolt-atom-v2))
+  (fields (mutable val) (mutable watches) (mutable validator) lock)
+  (nongenerative jolt-atom-v3))
 
 ;; (atom init) / (atom init :validator f :meta m): scan the trailing keyword opts
 ;; for :validator (the only one with runtime behaviour; :meta is accepted/ignored).
 (define (jolt-atom-new v . opts)
   (let loop ((o opts) (validator jolt-nil))
     (cond
-      ((or (null? o) (null? (cdr o))) (make-jolt-atom v '() validator))
+      ((or (null? o) (null? (cdr o))) (make-jolt-atom v '() validator (make-mutex)))
       ((and (keyword-t? (car o)) (string=? (keyword-t-name (car o)) "validator"))
        (loop (cddr o) (cadr o)))
       (else (loop (cddr o) validator)))))
@@ -50,37 +55,57 @@
     ((jolt-reduced? x) (jolt-reduced-val x))
     (else (error #f "deref: unsupported reference type" x))))
 
-;; (swap! a f arg*) -> (reset! a (f @a arg*)); f is invoked through jolt-invoke.
-;; Validate the new value BEFORE storing, notify watches AFTER (the seed order).
+;; CAS the val from `old` to `nv` by identity (eq?), atomically. Returns #t on
+;; success. The compute step (f) runs outside this, so we re-check under the lock.
+(define (jolt-atom-cas! a old nv)
+  (with-mutex (jolt-atom-lock a)
+    (if (eq? (jolt-atom-val a) old)
+        (begin (jolt-atom-val-set! a nv) #t)
+        #f)))
+
+;; (swap! a f arg*): JVM-style CAS loop — read, compute f OUTSIDE the lock, then
+;; atomically compare-and-set; retry if another thread changed it. Validate the
+;; new value before storing, notify watches after (the seed order).
 (define (jolt-swap! a f . args)
+  (let retry ()
     (let* ((old (jolt-atom-val a))
            (nv (apply jolt-invoke f old args)))
       (jolt-atom-validate a nv)
-    (jolt-atom-val-set! a nv)
-    (jolt-atom-notify a old nv)
-    nv))
+      (if (jolt-atom-cas! a old nv)
+          (begin (jolt-atom-notify a old nv) nv)
+          (retry)))))
 
 (define (jolt-reset! a v)
-  (let ((old (jolt-atom-val a)))
   (jolt-atom-validate a v)
-    (jolt-atom-val-set! a v)
+  (let ((old (with-mutex (jolt-atom-lock a)
+               (let ((o (jolt-atom-val a))) (jolt-atom-val-set! a v) o))))
     (jolt-atom-notify a old v)
     v))
 
+;; compare-and-set! keeps jolt= (value) semantics, done atomically under the lock.
 (define (jolt-compare-and-set! a oldv newv)
+  (jolt-atom-validate a newv)
+  (let ((swapped (with-mutex (jolt-atom-lock a)
                    (if (jolt= (jolt-atom-val a) oldv)
-      (begin (jolt-reset! a newv) #t)
-      #f))
+                       (begin (jolt-atom-val-set! a newv) #t)
+                       #f))))
+    (when swapped (jolt-atom-notify a oldv newv))
+    swapped))
 
 (define (jolt-swap-vals! a f . args)
+  (let retry ()
     (let* ((old (jolt-atom-val a))
            (nv (apply jolt-invoke f old args)))
-    (jolt-reset! a nv)
-    (jolt-vector old nv)))
+      (jolt-atom-validate a nv)
+      (if (jolt-atom-cas! a old nv)
+          (begin (jolt-atom-notify a old nv) (jolt-vector old nv))
+          (retry)))))
 
 (define (jolt-reset-vals! a v)
-  (let ((old (jolt-atom-val a)))
-    (jolt-reset! a v)
+  (jolt-atom-validate a v)
+  (let ((old (with-mutex (jolt-atom-lock a)
+               (let ((o (jolt-atom-val a))) (jolt-atom-val-set! a v) o))))
+    (jolt-atom-notify a old v)
     (jolt-vector old v)))
 
 ;; --- watches / validators (jolt-mn9o) ---------------------------------------

host/chez/concurrency.ss

@@ -0,0 +1,176 @@
+;; concurrency.ss (jolt-byjr) — real OS-thread futures + promises for the Chez host.
+;;
+;; SHARED-HEAP semantics (JVM Clojure), NOT Janet's isolated-heap snapshot: a
+;; future body runs on a native thread (fork-thread) over the SAME heap, so a
+;; captured atom is shared and the body's mutations are visible to the parent —
+;; matching `clojure.core` on the JVM. deref blocks on a mutex+condition latch.
+;;
+;; future / future-call / future-cancel / future? / future-done? / future-cancelled?
+;; promise / deliver, and the deref extension for both, are bound here (some
+;; re-asserted in post-prelude.ss over the overlay's Janet-shaped versions).
+;;
+;; pmap / pcalls / pvalues live in the clojure.core overlay (40-lazy) expressed
+;; over `future`, so they light up for free once future-call exists.
+;;
+;; Loaded near the end of rt.ss — after atoms.ss (jolt-deref, the atom lock) and
+;; dyn-binding.ss (the thread-local binding stack we convey into the worker).
+;; Requires a threaded Chez build (fork-thread / make-mutex / make-condition).
+
+;; --- time helpers -----------------------------------------------------------
+;; A relative duration / absolute deadline from a millisecond count (a jolt number).
+(define (ms->duration ms)
+  (let* ((ms* (exact (floor ms)))
+         (secs (quotient ms* 1000))
+         (nanos (* (remainder ms* 1000) 1000000)))
+    (make-time 'time-duration nanos secs)))
+(define (ms->deadline ms) (add-duration (current-time 'time-utc) (ms->duration ms)))
+
+;; --- futures ----------------------------------------------------------------
+;; A future is a mutable cell guarded by `mu`; workers/derefs coordinate on `cv`.
+;;   done?       — result (or cancellation) is final; derefs may proceed
+;;   cancelled?  — future-cancel won before the body finished
+;;   ok?         — payload is a value (else payload is a raised condition/value)
+;;   payload     — the result value, or the captured throw
+(define-record-type jolt-future
+  (fields (mutable done?) (mutable cancelled?) (mutable ok?) (mutable payload) mu cv)
+  (nongenerative jolt-future-v1))
+
+;; (future-call thunk): spawn a thread running (thunk). The dynamic bindings in
+;; effect now are conveyed into the worker (Chez inherits thread-parameters at
+;; fork; we also install an explicit snapshot for certainty). The result — value
+;; or thrown condition — is latched and broadcast; a cancel that already finalized
+;; the future makes the late result a no-op.
+(define (jolt-future-call thunk)
+  (let ((f (make-jolt-future #f #f #f jolt-nil (make-mutex) (make-condition)))
+        (snap (dyn-binding-stack)))
+    (fork-thread
+     (lambda ()
+       (dyn-binding-stack snap)
+       (let ((r (guard (e (#t (cons #f e))) (cons #t (jolt-invoke thunk)))))
+         (with-mutex (jolt-future-mu f)
+           (unless (jolt-future-done? f)            ; not already cancelled
+             (jolt-future-ok?-set! f (car r))
+             (jolt-future-payload-set! f (cdr r))
+             (jolt-future-done?-set! f #t))
+           (condition-broadcast (jolt-future-cv f))))))
+    f))
+
+;; Final value of a settled future (called OUTSIDE the lock): re-raise a captured
+;; throw, signal a cancellation, else the value.
+(define (jolt-future-finish f)
+  (cond
+    ((jolt-future-cancelled? f)
+     (jolt-throw (jolt-ex-info "Future cancelled" (jolt-hash-map))))
+    ((jolt-future-ok? f) (jolt-future-payload f))
+    (else (raise (jolt-future-payload f)))))
+
+(define (jolt-future-deref f)
+  (with-mutex (jolt-future-mu f)
+    (let loop ()
+      (unless (jolt-future-done? f)
+        (condition-wait (jolt-future-cv f) (jolt-future-mu f))
+        (loop))))
+  (jolt-future-finish f))
+
+;; (deref f timeout-ms timeout-val): wait up to timeout-ms; return timeout-val if
+;; it has not settled by the absolute deadline.
+(define (jolt-future-deref-timed f ms timeout-val)
+  (let* ((deadline (ms->deadline ms))
+         (settled (with-mutex (jolt-future-mu f)
+                    (let loop ()
+                      (cond ((jolt-future-done? f) #t)
+                            ((condition-wait (jolt-future-cv f) (jolt-future-mu f) deadline)
+                             (loop))                       ; woken — recheck
+                            (else (jolt-future-done? f))))))) ; timed out: final check
+    (if settled (jolt-future-finish f) timeout-val)))
+
+;; future-cancel: the running thread can't be interrupted, but the future object
+;; reflects the cancellation — if not already settled, mark it cancelled+done so
+;; derefs raise and the predicates flip. Returns true iff this call cancelled it.
+(define (jolt-future-cancel f)
+  (let ((cancelled (with-mutex (jolt-future-mu f)
+                     (if (jolt-future-done? f)
+                         #f
+                         (begin (jolt-future-cancelled?-set! f #t)
+                                (jolt-future-done?-set! f #t)
+                                (condition-broadcast (jolt-future-cv f))
+                                #t)))))
+    cancelled))
+
+(define (jolt-future-done?* f) (and (jolt-future? f) (jolt-future-done? f)))
+(define (jolt-native-future-done? x)
+  (if (jolt-future? x) (jolt-future-done? x)
+      (jolt-throw (jolt-ex-info "future-done? requires a future" (jolt-hash-map)))))
+(define (jolt-native-future-cancelled? x)
+  (and (jolt-future? x) (jolt-future-cancelled? x)))
+
+;; --- promises ---------------------------------------------------------------
+;; A blocking promise (JVM), not Janet's non-blocking atom shim: deref parks until
+;; deliver, then caches the value. deliver wins once; later delivers return nil.
+(define-record-type jolt-promise
+  (fields (mutable delivered?) (mutable value) mu cv)
+  (nongenerative jolt-promise-v1))
+
+(define (jolt-promise-new) (make-jolt-promise #f jolt-nil (make-mutex) (make-condition)))
+
+(define (jolt-deliver p v)
+  (if (jolt-promise? p)
+      (let ((won (with-mutex (jolt-promise-mu p)
+                   (if (jolt-promise-delivered? p)
+                       #f
+                       (begin (jolt-promise-value-set! p v)
+                              (jolt-promise-delivered?-set! p #t)
+                              (condition-broadcast (jolt-promise-cv p))
+                              #t)))))
+        (if won p jolt-nil))
+      (jolt-throw (jolt-ex-info "deliver requires a promise" (jolt-hash-map)))))
+
+(define (jolt-promise-deref p)
+  (with-mutex (jolt-promise-mu p)
+    (let loop ()
+      (unless (jolt-promise-delivered? p)
+        (condition-wait (jolt-promise-cv p) (jolt-promise-mu p))
+        (loop))))
+  (jolt-promise-value p))
+
+(define (jolt-promise-deref-timed p ms timeout-val)
+  (let* ((deadline (ms->deadline ms))
+         (got (with-mutex (jolt-promise-mu p)
+                (let loop ()
+                  (cond ((jolt-promise-delivered? p) #t)
+                        ((condition-wait (jolt-promise-cv p) (jolt-promise-mu p) deadline)
+                         (loop))
+                        (else (jolt-promise-delivered? p)))))))
+    (if got (jolt-promise-value p) timeout-val)))
+
+;; --- deref extension --------------------------------------------------------
+;; Chain the fully-built jolt-deref (atoms/vars/volatiles/reduced) with futures +
+;; promises, and accept the timed (deref ref ms val) arity for both.
+(define %pre-conc-deref jolt-deref)
+(set! jolt-deref
+  (lambda (x . opts)
+    (cond
+      ((jolt-future? x)
+       (if (null? opts) (jolt-future-deref x)
+           (jolt-future-deref-timed x (car opts) (cadr opts))))
+      ((jolt-promise? x)
+       (if (null? opts) (jolt-promise-deref x)
+           (jolt-promise-deref-timed x (car opts) (cadr opts))))
+      (else (apply %pre-conc-deref x opts)))))
+
+;; realized? for a Chez future/promise (the overlay reads Janet map keys). Wrap the
+;; overlay version in post-prelude.ss; here just the future/promise predicate.
+(define (jolt-conc-realized? x)
+  (cond ((jolt-future? x) (jolt-future-done? x))
+        ((jolt-promise? x) (jolt-promise-delivered? x))
+        (else #f)))
+
+;; --- bind into clojure.core -------------------------------------------------
+(def-var! "clojure.core" "future-call" jolt-future-call)
+(def-var! "clojure.core" "future-cancel" jolt-future-cancel)
+(def-var! "clojure.core" "future?" jolt-future?)
+(def-var! "clojure.core" "future-done?" jolt-native-future-done?)
+(def-var! "clojure.core" "future-cancelled?" jolt-native-future-cancelled?)
+(def-var! "clojure.core" "promise" jolt-promise-new)
+(def-var! "clojure.core" "deliver" jolt-deliver)
+(def-var! "clojure.core" "deref" jolt-deref)

host/chez/dyn-binding.ss

@@ -15,11 +15,15 @@
 ;; the stack before falling back to the cell root. Loaded LAST (after vars.ss and
 ;; ns.ss) so it chains the fully-extended jolt-var-get and overrides rt.ss var-deref.
 
-(define dyn-binding-stack '())
+;; THREAD-LOCAL (jolt-byjr): a Chez thread parameter, so each OS thread (a future
+;; / go block) has its own binding stack. Chez initializes a new thread's parameter
+;; to the spawning thread's value at fork time, giving Clojure binding conveyance
+;; for free (the future shim also installs an explicit snapshot, belt-and-suspenders).
+(define dyn-binding-stack (make-thread-parameter '()))
 
 ;; find the innermost (cell . value) pair binding CELL, or #f.
 (define (dyn-find-binding cell)
-  (let loop ((frames dyn-binding-stack))
+  (let loop ((frames (dyn-binding-stack)))
     (and (pair? frames)
          (or (assq cell (car frames))
              (loop (cdr frames))))))
@@ -28,7 +32,7 @@
 ;; value happens to be jolt-nil.
 (define dyn-no-binding (list 'no-binding))
 (define (dyn-binding-value cell)
-  (if (pair? dyn-binding-stack)
+  (if (pair? (dyn-binding-stack))
       (let ((p (dyn-find-binding cell)))
         (if p
             (let ((val (cdr p)))
@@ -39,21 +43,21 @@
 ;; push-thread-bindings: frame is a jolt map of var-cell -> value. Fold it into an
 ;; identity-keyed alist of mutable pairs and push.
 (define (jolt-push-thread-bindings frame)
-  (set! dyn-binding-stack
+  (dyn-binding-stack
    (cons (pmap-fold frame (lambda (k v acc) (cons (cons k v) acc)) '())
-              dyn-binding-stack))
+         (dyn-binding-stack)))
   jolt-nil)
 
 (define (jolt-pop-thread-bindings)
-  (when (pair? dyn-binding-stack)
-    (set! dyn-binding-stack (cdr dyn-binding-stack)))
+  (when (pair? (dyn-binding-stack))
+    (dyn-binding-stack (cdr (dyn-binding-stack))))
   jolt-nil)
 
 ;; get-thread-bindings: a jolt map of every currently-bound cell -> value,
 ;; innermost wins. Merge oldest-frame-first (the stack head is innermost). The
 ;; result can be re-pushed by with-bindings* / bound-fn*.
 (define (jolt-get-thread-bindings)
-  (let loop ((frames (reverse dyn-binding-stack)) (m (jolt-hash-map)))
+  (let loop ((frames (reverse (dyn-binding-stack))) (m (jolt-hash-map)))
     (if (null? frames)
         m
         (loop (cdr frames)

host/chez/host-static.ss

@@ -128,9 +128,16 @@
         (cons "PI" (->num (* 4 (atan 1)))) (cons "E" (->num (exp 1)))
         (cons "random" (lambda args (->num (random 1.0))))))
 
-;; Thread: no real threading here (futures/timing are jolt-byjr). sleep is a no-op.
+;; Thread: real OS threads back futures/promises (jolt-byjr), so sleep genuinely
+;; parks the calling thread for `ms` milliseconds (a worker sleeping doesn't block
+;; the parent). yield hands off the scheduler.
 (register-class-statics! "Thread"
-  (list (cons "sleep" (lambda (ms . _) jolt-nil))
+  (list (cons "sleep" (lambda (ms . _)
+                        (let* ((ms* (exact (floor ms)))
+                               (secs (quotient ms* 1000))
+                               (nanos (* (remainder ms* 1000) 1000000)))
+                          (sleep (make-time 'time-duration nanos secs)))
+                        jolt-nil))
         (cons "yield" (lambda () jolt-nil))
         (cons "interrupted" (lambda () #f))
         (cons "currentThread" (lambda () (make-jhost "thread" '())))))

host/chez/post-prelude.ss

@@ -38,3 +38,20 @@
 ;; ns-name: the overlay reads (get ns :name) — nil on a jns namespace record.
 ;; Native version (defined in ns.ss) returns the namespace's name symbol.
 (def-var! "clojure.core" "ns-name" jolt-ns-name)
+;; concurrency (jolt-byjr): the overlay's future-done?/future-cancelled?/realized?
+;; read a Janet future-map's :cached/:cancelled keys, and promise/deliver are a
+;; non-blocking atom shim. A Chez future/promise is a record, and we want JVM
+;; (blocking, shared-heap) semantics — re-assert the native versions. realized?
+;; wraps the overlay (which still handles delay/lazy-seq/atom) for non-futures.
+(def-var! "clojure.core" "future-done?" jolt-native-future-done?)
+(def-var! "clojure.core" "future-cancelled?" jolt-native-future-cancelled?)
+(def-var! "clojure.core" "future?" jolt-future?)
+(def-var! "clojure.core" "promise" jolt-promise-new)
+(def-var! "clojure.core" "deliver" jolt-deliver)
+(def-var! "clojure.core" "deref" jolt-deref)
+(let ((overlay-realized? (var-deref "clojure.core" "realized?")))
+  (def-var! "clojure.core" "realized?"
+    (lambda (x)
+      (if (or (jolt-future? x) (jolt-promise? x))
+          (jolt-conc-realized? x)
+          (jolt-invoke overlay-realized? x)))))

host/chez/rt.ss

@@ -325,3 +325,9 @@
 ;; on Chez, inc6b) calls these to build its expansion as reader forms. Needs the
 ;; collection/seq layer + def-var!; order-independent past those.
 (load "host/chez/syntax-quote.ss")
+
+;; concurrency (jolt-byjr): real OS-thread futures + blocking promises, shared-heap
+;; (JVM) semantics. Loaded LAST — chains the fully-built jolt-deref and conveys the
+;; thread-local binding stack (dyn-binding.ss) into workers. pmap/pcalls/pvalues
+;; (overlay, over `future`) light up once future-call exists here.
+(load "host/chez/concurrency.ss")

host/chez/seed/prelude.ss

@@ -945,7 +945,7 @@
 (guard (e (#t #f))
   (def-var! "clojure.core" "take-nth" (letrec ((take-nth (case-lambda ((n) (let fnrec177 ((n n)) (lambda (rf) (let fnrec178 ((rf rf)) (let* ((iv (jolt-invoke (var-deref "clojure.core" "volatile!") -1.0))) (case-lambda (() (let fnrec179 () (jolt-invoke rf ))) ((result) (let fnrec180 ((result result)) (jolt-invoke rf result))) ((result input) (let fnrec181 ((result result) (input input)) (let* ((i (jolt-invoke (var-deref "clojure.core" "vswap!") iv jolt-inc))) (if (jolt-zero? (remainder i n)) (jolt-invoke rf result input) result)))))))))) ((n coll) (let fnrec182 ((n n) (coll coll)) (jolt-invoke (var-deref "clojure.core" "make-lazy-seq") (lambda () (let fnrec183 () (jolt-invoke (var-deref "clojure.core" "coll->cells") (let* ((temp__15__auto (jolt-seq coll))) (if (jolt-truthy? temp__15__auto) (let* ((s temp__15__auto)) (jolt-cons (jolt-first s) (jolt-invoke take-nth n (jolt-drop n s)))) jolt-nil))))))))))) take-nth)))
 (guard (e (#t #f))
-  (def-var! "clojure.core" "pmap" (letrec ((pmap (case-lambda ((f coll) (let fnrec184 ((f f) (coll coll)) (jolt-map (var-deref "clojure.core" "deref") (jolt-invoke (var-deref "clojure.core" "doall") (jolt-map (lambda (x) (let fnrec185 ((x x)) (host-static-call "clojure.core" "future-call" (lambda () (let fnrec186 () (jolt-invoke f x)))))) coll))))) ((f coll . colls) (let fnrec187 ((f f) (coll coll) (colls (list->cseq colls))) (jolt-invoke pmap (lambda (xs) (let fnrec188 ((xs xs)) (jolt-apply f xs))) (jolt-apply jolt-map jolt-vector coll colls))))))) pmap)))
+  (def-var! "clojure.core" "pmap" (letrec ((pmap (case-lambda ((f coll) (let fnrec184 ((f f) (coll coll)) (jolt-map (var-deref "clojure.core" "deref") (jolt-invoke (var-deref "clojure.core" "doall") (jolt-map (lambda (x) (let fnrec185 ((x x)) (jolt-invoke (var-deref "clojure.core" "future-call") (lambda () (let fnrec186 () (jolt-invoke f x)))))) coll))))) ((f coll . colls) (let fnrec187 ((f f) (coll coll) (colls (list->cseq colls))) (jolt-invoke pmap (lambda (xs) (let fnrec188 ((xs xs)) (jolt-apply f xs))) (jolt-apply jolt-map jolt-vector coll colls))))))) pmap)))
 (guard (e (#t #f))
   (def-var! "clojure.core" "pcalls" (letrec ((pcalls (lambda fns (let fnrec189 ((fns (list->cseq fns))) (jolt-invoke (var-deref "clojure.core" "pmap") (lambda (f) (let fnrec190 ((f f)) (jolt-invoke f ))) fns))))) pcalls)))
 (guard (e (#t #f))

test/chez/cli-test.janet

@@ -47,7 +47,28 @@
    ["(map eval [(quote (+ 1 1)) (quote (* 3 3))])" "(2 9)"]
    ["(defmacro add1 [x] (list (quote +) x 1)) (add1 10)" "11"]
    ["(defmacro twice [x] `(do ~x ~x)) (twice (+ 2 3))" "5"]
-   ["(defmacro m [x] `(+ ~x 1)) (m (m (m 0)))" "3"]])
+   ["(defmacro m [x] `(+ ~x 1)) (m (m (m 0)))" "3"]
+   # jolt-byjr: concurrency — futures/pmap/promise on real OS threads (shared heap).
+   ["(deref (future (+ 1 2)))" "3"]
+   ["@(future (* 6 7))" "42"]
+   ["(deref (future (mapv inc [1 2 3])))" "[2 3 4]"]
+   ["(let [f (future (+ 1 1))] [(deref f) (deref f)])" "[2 2]"]
+   ["(future? (future 1))" "true"]
+   ["(future? 42)" "false"]
+   ["(let [f (future 1)] (deref f) (future-done? f))" "true"]
+   ["(let [f (future 1)] (deref f) (realized? f))" "true"]
+   ["(let [f (future 42)] (deref f) (deref f 1000 :nope))" "42"]
+   ["(vec (pmap inc [1 2 3]))" "[2 3 4]"]
+   ["(vec (pmap + [1 2 3] [4 5 6]))" "[5 7 9]"]
+   ["(vec (pcalls (fn [] 1) (fn [] 2)))" "[1 2]"]
+   ["(vec (pvalues (+ 1 2) (+ 3 4)))" "[3 7]"]
+   # shared heap = JVM semantics (NOT Janet's isolated-heap snapshot): a captured
+   # atom is shared, so the future's swap! is visible to the parent.
+   ["(let [a (atom 0)] (deref (future (swap! a inc))) @a)" "1"]
+   ["(let [a (atom 0)] (dorun (pmap (fn [_] (swap! a inc)) [1 2 3 4])) @a)" "4"]
+   # promise blocks until delivered (JVM), unlike the Janet atom-shim.
+   ["(let [p (promise)] (deliver p 7) @p)" "7"]
+   ["(let [p (promise)] (future (deliver p :hi)) @p)" ":hi"]])
 
 (each [src want] cases
   (def [code out err] (joltc src))

test/chez/run-corpus-prelude.janet

@@ -91,7 +91,22 @@
    "atom?" true
    # Same atom-class gap, via the folded-in conformance case (jolt-ohtd):
    # (instance? clojure.lang.Atom (atom 1)).
-   "instance? Atom" true})
+   "instance? Atom" true
+   # concurrency (jolt-byjr): the Chez runtime now uses real OS-thread futures
+   # sharing the heap = JVM semantics, NOT Janet's isolated-heap snapshot. So a
+   # captured atom is shared (the corpus :expected is the Janet snapshot value).
+   # Deliberate per jvm-parity-north-star. Same allowlist as the zero-Janet gate.
+   "captured atom is snapshotted, not shared" true   # Chez 1 (shared) vs Janet 0
+   "snapshot semantics" true                          # pmap: Chez 2 (shared) vs Janet 0
+   # future-cancel of a trivial body races the worker under real threads (cancel
+   # usually loses -> false), like the JVM; the Janet :expected relies on its
+   # cooperative scheduler. Flaky/divergent.
+   "cancel an in-flight future returns true" true
+   "future-cancelled? after cancel" true})
+
+# Cases that BLOCK forever on a shared-heap / JVM host (profile.edn :bucket
+# :timeout) — skip, like :throws, so a hung per-case process can't stall the gate.
+(def skip-blocking {"promise undelivered" true})
 
 (def ctx (d/make-ctx))
 
@@ -130,7 +145,7 @@
 (def t1 (os/clock))
 (each row cases
   (def {:expected e :actual a :label l} row)
-  (if (= e :throws)
+  (if (or (= e :throws) (get skip-blocking l))
     nil  # :throws error-semantics aren't modeled here; skip (counted out of run)
     (let [src (string "(= " e " " a ")")
           res (d/eval-e-with-prelude ctx src prelude-path)]

test/chez/run-corpus-zero-janet.janet

@@ -78,7 +78,24 @@
     "inf inside coll" true
     # #?@ reader-conditional splicing into the enclosing seq isn't supported yet
     # (plain #? works); a single niche corpus case.
-    "reader cond splice" true})
+    "reader cond splice" true
+    # concurrency (jolt-byjr): Chez futures are real OS threads sharing the heap =
+    # JVM semantics, NOT Janet's isolated-heap snapshot. So a captured atom IS
+    # shared (the corpus :expected is the Janet snapshot value). Deliberate per the
+    # jvm-parity-north-star — Chez matches the JVM, Janet keeps the old snapshot.
+    "captured atom is snapshotted, not shared" true   # Chez 1 (shared) vs Janet 0
+    "snapshot semantics" true                          # pmap: Chez 2 (shared) vs Janet 0
+    # future-cancel on a trivial body is timing-dependent under real threads: the
+    # future usually completes before the cancel (cancel -> false), like the JVM.
+    # The Janet :expected "true" relies on cooperative scheduling. Flaky/divergent.
+    "cancel an in-flight future returns true" true
+    "future-cancelled? after cancel" true})
+
+# Cases that BLOCK forever on a shared-heap / JVM host (profile.edn :bucket
+# :timeout) — skip them, like :throws: a single hung case would stall the whole
+# batched process. (deref of an undelivered promise blocks on the JVM and now on
+# Chez; Janet's non-blocking atom-shim returned nil.)
+(def skip-blocking @{"promise undelivered" true})
 
 (var pass 0)
 (def crashes @[])      # nonzero chez exit (analyzer/emitter raised, or runtime gap)
@@ -116,8 +133,8 @@
 (def rows-by-idx @{})
 (def pairs @[])
 (eachp [i row] cases
-  (def {:expected e :actual a} row)
-  (if (= e :throws)
+  (def {:expected e :actual a :label l} row)
+  (if (or (= e :throws) (get skip-blocking l))
     (++ throws)
     (let [key (string i)]
       (put rows-by-idx key row)
@@ -166,7 +183,7 @@
 
 # Regression floor: raise as the Chez-hosted compiler closes gaps. The gate fails
 # on any NEW divergence or if pass drops below the floor. Strided runs scale to 0.
-(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_ZJ_FLOOR") "2544")))
+(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_ZJ_FLOOR") "2569")))
 (def floor (if (os/getenv "JOLT_CORPUS_LIMIT") 0 base-floor))
 (when (or (> (length diverged) 0) (< pass floor))
   (printf "REGRESSION: pass %d < floor %d or %d new divergence(s)" pass floor (length diverged)))