From 6db1bdda1ba79bd97aed783957068cc069c5a98a Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Mon, 9 Dec 2019 06:24:11 -0700
Subject: [PATCH] cs: fix `touch` on a future blocked on a fsemaphore

Relevant to #2957
---
 pkgs/racket-test/tests/future/fsemaphore.rkt | 18 ++++++++++++++++++
 racket/src/thread/future-object.rkt          |  2 +-
 racket/src/thread/future.rkt                 |  2 +-
 3 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 pkgs/racket-test/tests/future/fsemaphore.rkt

diff --git a/pkgs/racket-test/tests/future/fsemaphore.rkt b/pkgs/racket-test/tests/future/fsemaphore.rkt
new file mode 100644
index 0000000000..8fb3ea8f07
--- /dev/null
+++ b/pkgs/racket-test/tests/future/fsemaphore.rkt
@@ -0,0 +1,18 @@
+#lang racket
+
+;; Check `touch` on a future blocked on an fsemaphore
+
+(define mutex (make-fsemaphore 1))
+
+(define futures
+  (for/list ([i 10])
+    (future
+     (lambda ()
+       (fsemaphore-wait mutex)
+       (println (add1 i))
+       (fsemaphore-post mutex)))))
+
+(void
+ (map sync
+      (for/list ([f (in-list futures)])
+        (thread (lambda () (touch f))))))
diff --git a/racket/src/thread/future-object.rkt b/racket/src/thread/future-object.rkt
index e309ee4e51..40536a7808 100644
--- a/racket/src/thread/future-object.rkt
+++ b/racket/src/thread/future-object.rkt
@@ -17,7 +17,7 @@
                  [prev #:mutable]   ; queue previous
                  [next #:mutable]   ; queue next
                  [results #:mutable]
-                 [state #:mutable]  ; #f (could run), 'running, 'blocked, 'done, 'aborted, 'fsema, or future waiting on
+                 [state #:mutable]  ; #f (could run), 'running, 'blocked, 'done, 'aborted, 'fsema or box, or future waiting on
                  [dependents #:mutable]) ; futures that are blocked on this one
   #:authentic
   #:reflection-name 'future)
diff --git a/racket/src/thread/future.rkt b/racket/src/thread/future.rkt
index 0ca527d7e3..9439eeb75c 100644
--- a/racket/src/thread/future.rkt
+++ b/racket/src/thread/future.rkt
@@ -287,7 +287,7 @@
         (lock-release (future*-lock f))
         (touch s)
         (touch f)])]
-    [(box? s) ; => dependent on fsemaphore
+    [(or (box? s) (eq? s 'fsema)) ; => dependent on fsemaphore
      (cond
        [(current-future)
         ;; Lots to wait on, so give up on the current future for now