From 90388d154921d27877e9166619b9ecff83340325 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Sun, 24 Nov 2013 08:13:08 -0700
Subject: [PATCH] fix handling of choice evt returned by a guard evt

Closes PR 14195

Merge to v6.0
---
 .../racket-test/tests/racket/sync.rktl        | 22 +++++++++++++++++++
 racket/src/racket/src/thread.c                | 13 +++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/pkgs/racket-pkgs/racket-test/tests/racket/sync.rktl b/pkgs/racket-pkgs/racket-test/tests/racket/sync.rktl
index 7820fb6eef..9a2014d0f5 100644
--- a/pkgs/racket-pkgs/racket-test/tests/racket/sync.rktl
+++ b/pkgs/racket-pkgs/racket-test/tests/racket/sync.rktl
@@ -241,6 +241,28 @@
   (test 0.15 sync/timeout 18 
 	(choice-evt (make-delay 0.2) (make-delay 0.15))))
 
+;;check flattening of choice evts returned by a guard:
+(let ()
+  (define s1 (make-semaphore))
+  (define s2 (make-semaphore))
+  (define s3 (make-semaphore))
+  (define s4 (make-semaphore))
+  
+  (define evt1 (choice-evt s1 s2))
+  (define evt2 (choice-evt s3 s4))
+
+  (thread (lambda () 
+            (sync (system-idle-evt))
+            (semaphore-post
+             (list-ref (list s1 s2 s3 s4)
+                       (random 4)))))
+
+  (test #t
+        semaphore?
+        (sync (guard-evt
+               (lambda ()
+                 (choice-evt evt1 evt2))))))
+
 ;; ----------------------------------------
 ;; Wrapped waitables
 
diff --git a/racket/src/racket/src/thread.c b/racket/src/racket/src/thread.c
index 9976c87f83..ca0b72b140 100644
--- a/racket/src/racket/src/thread.c
+++ b/racket/src/racket/src/thread.c
@@ -5947,6 +5947,7 @@ void scheme_clear_thread_sync(Scheme_Thread *p)
 /*========================================================================*/
 
 static void syncing_needs_wakeup(Scheme_Object *s, void *fds);
+static Evt_Set *make_evt_set(const char *name, int argc, Scheme_Object **argv, int delta, int flatten);
 
 typedef struct Evt {
   MZTAG_IF_REQUIRED
@@ -6168,7 +6169,15 @@ static void set_sync_target(Syncing *syncing, int i, Scheme_Object *target,
 
   if (SCHEME_EVTSETP(target) && retry) {
     /* Flatten the set into this one */
-    Evt_Set *wts = (Evt_Set *)target;
+    Evt_Set *wts;
+
+    if (SCHEME_EVTSET_UNFLATTENEDP(target)) {
+      Scheme_Object *a[1];
+      a[0] = target;
+      wts = make_evt_set("sync", 1, a, 0, 1);
+    } else
+      wts = (Evt_Set *)target;
+
     if (wts->argc == 1) {
       /* 1 thing in set? Flattening is easy! */
       evt_set->argv[i] = wts->argv[0];
@@ -6486,7 +6495,7 @@ static int evt_set_flatten(Evt_Set *e, int pos, Scheme_Object **args, Evt **ws)
   return pos;
 }
 
-Evt_Set *make_evt_set(const char *name, int argc, Scheme_Object **argv, int delta, int flatten)
+static Evt_Set *make_evt_set(const char *name, int argc, Scheme_Object **argv, int delta, int flatten)
 {
   Evt *w, **iws, **ws;
   Evt_Set *evt_set, *subset;