Add an refresh probability comment to worthRefreshPopular()

[lhc/web/wiklou.git] / includes / libs / objectcache / WANObjectCache.php

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index e7c4edb..eec5fc6 100644 (file)
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -88,6 +88,8 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
        /** @var int ERR_* constant for the "last error" registry */
        protected $lastRelayError = self::ERR_NONE;
 
+       /** @var integer Callback stack depth for getWithSetCallback() */
+       private $callbackDepth = 0;
        /** @var mixed[] Temporary warm-up cache */
        private $warmupCache = [];
 
@@ -847,8 +849,10 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
        final public function getWithSetCallback( $key, $ttl, $callback, array $opts = [] ) {
                $pcTTL = isset( $opts['pcTTL'] ) ? $opts['pcTTL'] : self::TTL_UNCACHEABLE;
 
-               // Try the process cache if enabled
-               if ( $pcTTL >= 0 ) {
+               // Try the process cache if enabled and the cache callback is not within a cache callback.
+               // Process cache use in nested callbacks is not lag-safe with regard to HOLDOFF_TTL since
+               // the in-memory value is further lagged than the shared one since it uses a blind TTL.
+               if ( $pcTTL >= 0 && $this->callbackDepth == 0 ) {
                        $group = isset( $opts['pcGroup'] ) ? $opts['pcGroup'] : self::PC_PRIMARY;
                        $procCache = $this->getProcessCache( $group );
                        $value = $procCache->get( $key );
@@ -995,7 +999,12 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 
                // Generate the new value from the callback...
                $setOpts = [];
-               $value = call_user_func_array( $callback, [ $cValue, &$ttl, &$setOpts, $asOf ] );
+               ++$this->callbackDepth;
+               try {
+                       $value = call_user_func_array( $callback, [ $cValue, &$ttl, &$setOpts, $asOf ] );
+               } finally {
+                       --$this->callbackDepth;
+               }
                // When delete() is called, writes are write-holed by the tombstone,
                // so use a special INTERIM key to pass the new value around threads.
                if ( ( $isTombstone && $lockTSE > 0 ) && $value !== false && $ttl >= 0 ) {
@@ -1349,7 +1358,9 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
                        return false;
                }
 
-               // Lifecycle is: new, ramp-up refresh chance, full refresh chance
+               // Lifecycle is: new, ramp-up refresh chance, full refresh chance.
+               // Note that the "expected # of refreshes" for the ramp-up time range is half of what it
+               // would be if P(refresh) was at its full value during that time range.
                $refreshWindowSec = max( $timeTillRefresh - $ageNew - self::RAMPUP_TTL / 2, 1 );
                // P(refresh) * (# hits in $refreshWindowSec) = (expected # of refreshes)
                // P(refresh) * ($refreshWindowSec * $popularHitsPerSec) = 1