Imported from /home/lorry/working-area/delta_berkeleydb/db-6.1.23.tar.gz.HEADdb-6.1.23master

1 files changed, 12 insertions, 1 deletions

diff --git a/src/dbinc/shqueue.h b/src/dbinc/shqueue.h
index 22464462..20e0fae7 100644
--- a/src/dbinc/shqueue.h
+++ b/src/dbinc/shqueue.h
@@ -1,7 +1,7 @@
 /*-
  * See the file LICENSE for redistribution information.
  *
- * Copyright (c) 1996, 2012 Oracle and/or its affiliates.  All rights reserved.
+ * Copyright (c) 1996, 2015 Oracle and/or its affiliates.  All rights reserved.
  *
  * $Id$
  */
@@ -140,6 +140,17 @@ struct {								\
 	((struct type *)(((u_int8_t *)(elm)) + (elm)->field.sle_next)))
 
   /*
+   * __SH_LIST_WAS_EMPTY is private API.  SH_LIST_FIRST is not thread-safe;
+   * the slh_first field could be evaluated multiple times if the optimizer
+   * does not eliminate the second load.  __SH_LIST_WAS_EMPTY tests whether a
+   * prior call of SH_LIST_FIRSTP occurred while the list was empty; i.e., its
+   * relative offset was -1. It is thread-safe to call SH_LIST_FIRSTP and then
+   * test the resulting pointer with __SH_LIST_WAS_EMPTY.
+ */
+#define	__SH_LIST_WAS_EMPTY(head, ptr)					\
+	((u_int8_t *)(ptr) == (((u_int8_t *)(head)) + (-1)))
+
+  /*
    *__SH_LIST_PREV_OFF is private API.  It calculates the address of
    * the elm->field.sle_next member of a SH_LIST structure.  All offsets
    * between elements are relative to that point in SH_LIST structures.