From 6d4c25a32241117f0f49d2f071c202906a33bbf2 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 1 May 2014 19:01:10 -0600
Subject: [PATCH] places: fix gc of place channels containing place channels

The bug was a kind of typo: using `&` where `%` was intended to
implement a counter wraparound.

This bug is an even more likely candidate to be resopnsible for the
occassional crashes from the DrRacket easter-egg test.
---
 .../racket-test/tests/racket/place-chmsg-gc.rkt | 17 +++++++++++++++++
 racket/src/racket/src/mzmark_place.inc          |  4 ++--
 racket/src/racket/src/mzmarksrc.c               |  2 +-
 3 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 pkgs/racket-pkgs/racket-test/tests/racket/place-chmsg-gc.rkt

diff --git a/pkgs/racket-pkgs/racket-test/tests/racket/place-chmsg-gc.rkt b/pkgs/racket-pkgs/racket-test/tests/racket/place-chmsg-gc.rkt
new file mode 100644
index 0000000000..8dac94d01f
--- /dev/null
+++ b/pkgs/racket-pkgs/racket-test/tests/racket/place-chmsg-gc.rkt
@@ -0,0 +1,17 @@
+#lang racket/base
+(require racket/place)
+
+;; Make sure that place channels waiting in a channel
+;; are kept properly. N should be large enough to trigger
+;; a master collection.
+
+(define N 10000)
+(define-values (i o) (place-channel))
+(for ([j N])
+  (define-values (i2 o2) (place-channel))
+  (place-channel-put i2 j)
+  (place-channel-put i o2))
+(for ([j N])
+  (unless (eq? j (place-channel-get (place-channel-get o)))
+    ;; just as likely to crash as get here
+    (error "failed")))
diff --git a/racket/src/racket/src/mzmark_place.inc b/racket/src/racket/src/mzmark_place.inc
index 93c0e2a70d..70b119d937 100644
--- a/racket/src/racket/src/mzmark_place.inc
+++ b/racket/src/racket/src/mzmark_place.inc
@@ -102,7 +102,7 @@ static int place_async_channel_val_MARK(void *p, struct NewGC *gc) {
       gcMARK2(SCHEME_CAR(pr), gc);
       pr = SCHEME_CDR(pr);
     }
-    j = ((j + 1) & sz);
+    j = ((j + 1) % sz);
   }
 
   return
@@ -127,7 +127,7 @@ static int place_async_channel_val_FIXUP(void *p, struct NewGC *gc) {
       gcFIXUP2(SCHEME_CAR(pr), gc);
       pr = SCHEME_CDR(pr);
     }
-    j = ((j + 1) & sz);
+    j = ((j + 1) % sz);
   }
 
   return
diff --git a/racket/src/racket/src/mzmarksrc.c b/racket/src/racket/src/mzmarksrc.c
index 7d926e241f..a4bf998059 100644
--- a/racket/src/racket/src/mzmarksrc.c
+++ b/racket/src/racket/src/mzmarksrc.c
@@ -1601,7 +1601,7 @@ place_async_channel_val {
       gcMARK2(SCHEME_CAR(pr), gc);
       pr = SCHEME_CDR(pr);
     }
-    j = ((j + 1) & sz);
+    j = ((j + 1) % sz);
   }
 
  size: