Added a tombstone comment to WANObjectCache

Change-Id: Ia8c2fc4d4bbb741a6cd7aaa6f3ae433e65743b29

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index e8837b3..2d54681 100644 (file)
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -258,7 +258,9 @@ class WANObjectCache {
         *
         * This instantiates a hold-off period where the key cannot be
         * written to avoid race conditions where dependent keys get updated
-        * with a stale value (e.g. from a DB slave).
+        * with a stale value (e.g. from a DB slave). This is implemented by
+        * storing a special "tombstone" value at the cache key that this
+        * class recognizes; get() calls will return false for the key.
         *
         * This should only be called when the underlying data (being cached)
         * changes in a significant way. If called twice on the same key, then