Subject: bug#28590: [PATCH 3/7] weak-table: Make sure 'move_disappearing_links' actually moves links.

From: Ludovic Courtès <[email-masked]>
Date: Tue, 3 Oct 2017 13:43:48 +0200

* libguile/weak-table.c (move_disappearing_links): Check the return
value of 'GC_move_disappearing_link' and call
'register_disappearing_links' upon GC_NOT_FOUND.
(GC_move_disappearing_link) [!HAVE_GC_MOVE_DISAPPEARING_LINK]: Adjust
to return the error code.
---
 libguile/weak-table.c | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/libguile/weak-table.c b/libguile/weak-table.c
index 1aa2a0fcc..7d8633165 100644
--- a/libguile/weak-table.c
+++ b/libguile/weak-table.c
@@ -153,11 +153,16 @@ unregister_disappearing_links (scm_t_weak_entry *entry,
 }
 
 #ifndef HAVE_GC_MOVE_DISAPPEARING_LINK
-static void
+static int
 GC_move_disappearing_link (void **from, void **to)
 {
-  GC_unregister_disappearing_link (from);
-  SCM_I_REGISTER_DISAPPEARING_LINK (to, *to);
+  int err;
+
+  err = GC_unregister_disappearing_link (from);
+  if (err == GC_SUCCESS)
+    err = SCM_I_REGISTER_DISAPPEARING_LINK (to, *to);
+
+  return err;
 }
 #endif
 
@@ -165,13 +170,33 @@ static void
 move_disappearing_links (scm_t_weak_entry *from, scm_t_weak_entry *to,
                          SCM key, SCM value, scm_t_weak_table_kind kind)
 {
+  int err;
+
   if ((kind == SCM_WEAK_TABLE_KIND_KEY || kind == SCM_WEAK_TABLE_KIND_BOTH)
       && SCM_HEAP_OBJECT_P (key))
-    GC_move_disappearing_link ((void **) &from->key, (void **) &to->key);
+    {
+      err = GC_move_disappearing_link ((void **) &from->key,
+				       (void **) &to->key);
+      if (err == GC_NOT_FOUND)
+	/* Link disappeared.  */
+	register_disappearing_links (to, key, value,
+				     SCM_WEAK_TABLE_KIND_KEY);
+      else
+	assert (err == GC_SUCCESS);
+    }
 
   if ((kind == SCM_WEAK_TABLE_KIND_VALUE || kind == SCM_WEAK_TABLE_KIND_BOTH)
       && SCM_HEAP_OBJECT_P (value))
-    GC_move_disappearing_link ((void **) &from->value, (void **) &to->value);
+    {
+      err = GC_move_disappearing_link ((void **) &from->value,
+				       (void **) &to->value);
+      if (err == GC_NOT_FOUND)
+	/* Link disappeared.  */
+	register_disappearing_links (to, key, value,
+				     SCM_WEAK_TABLE_KIND_VALUE);
+      else
+	assert (err == GC_SUCCESS);
+    }
 }
 
 static void
-- 
2.14.2