Added more lockTSE comments to getWithSetCallback()

Change-Id: I6ac56784bc231d7dec7869c6d2b901341bde6e9b

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index 7f55456..92bd0bd 100755 (executable)
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -361,10 +361,12 @@ class WANObjectCache {
         *   - lowTTL  : consider pre-emptive updates when the current TTL (sec)
         *               of the key is less than this. It becomes more likely
         *               over time, becoming a certainty once the key is expired.
-        *   - lockTSE : if the key is tombstoned or expired less (by $checkKeys)
+        *   - lockTSE : if the key is tombstoned or expired (by $checkKeys) less
         *               than this many seconds ago, then try to have a single
         *               thread handle cache regeneration at any given time.
         *               Other threads will try to use stale values if possible.
+        *               If, on miss, the time since expiration is low, the assumption
+        *               is that the key is hot and that a stampede is worth avoiding.
         *   - tempTTL : when 'lockTSE' is set, this determines the TTL of the temp
         *               key used to cache values while a key is tombstoned.
         *               This avoids excessive regeneration of hot keys on delete() but