From 4db819011aa95f61de7f19d47ce8c280a0f9d9c0 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Mon, 11 May 2015 10:03:55 -0700
Subject: [PATCH] Allow for dynamic TTLs in getWithSetCallback()

* This gives it better parity with BagOStuff::set()
* Also updated some doc comments

Change-Id: Ib94b97715fae901bac1750656e3dc7501919d6d2
---
 includes/libs/objectcache/WANObjectCache.php        | 13 ++++++++-----
 .../includes/objectcache/WANObjectCacheTest.php     | 11 ++++++++++-
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index 92bd0bdfa6..21a09e6c21 100755
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -300,10 +300,13 @@ class WANObjectCache {
 	/**
 	 * Method to fetch/regenerate cache keys
 	 *
-	 * On cache miss, the key will be set to the callback result.
+	 * On cache miss, the key will be set to the callback result,
+	 * unless the callback returns false. The arguments supplied are:
+	 *     (current value or false, &$ttl)
 	 * The callback function returns the new value given the current
-	 * value (false if not present). If false is returned, then nothing
-	 * will be saved to cache.
+	 * value (false if not present). Preemptive re-caching and $checkKeys
+	 * can result in a non-false current value. The TTL of the new value
+	 * can be set dynamically by altering $ttl in the callback (by reference).
 	 *
 	 * Usually, callbacks ignore the current value, but it can be used
 	 * to maintain "most recent X" values that come from time or sequence
@@ -326,7 +329,7 @@ class WANObjectCache {
 	 * @code
 	 *     $key = wfMemcKey( 'cat-recent-actions', $catId );
 	 *     // Function that derives the new key value given the old value
-	 *     $callback = function( $cValue ) { ... };
+	 *     $callback = function( $cValue, &$ttl ) { ... };
 	 *     // Get the key value from cache or from source on cache miss;
 	 *     // try to only let one cluster thread manage doing cache updates
 	 *     $opts = array( 'lockTSE' => 5, 'lowTTL' => 10 );
@@ -419,7 +422,7 @@ class WANObjectCache {
 		}
 
 		// Generate the new value from the callback...
-		$value = call_user_func( $callback, $cValue );
+		$value = call_user_func_array( $callback, array( $cValue, &$ttl ) );
 		// When delete() is called, writes are write-holed by the tombstone,
 		// so use a special stash key to pass the new value around threads.
 		if ( $value !== false && ( $isHot || $isTombstone ) ) {
diff --git a/tests/phpunit/includes/objectcache/WANObjectCacheTest.php b/tests/phpunit/includes/objectcache/WANObjectCacheTest.php
index 3161d18aca..3e284c8110 100644
--- a/tests/phpunit/includes/objectcache/WANObjectCacheTest.php
+++ b/tests/phpunit/includes/objectcache/WANObjectCacheTest.php
@@ -86,13 +86,22 @@ class WANObjectCacheTest extends MediaWikiTestCase {
 		$cKey2 = wfRandomString();
 
 		$wasSet = 0;
-		$func = function() use ( &$wasSet, $value ) { ++$wasSet; return $value; };
+		$func = function( $old, &$ttl ) use ( &$wasSet, $value ) {
+			++$wasSet;
+			$ttl = 20; // override with another value
+			return $value;
+		};
 
 		$wasSet = 0;
 		$v = $cache->getWithSetCallback( $key, $func, 30, array(), array( 'lockTSE' => 5 ) );
 		$this->assertEquals( $v, $value );
 		$this->assertEquals( 1, $wasSet, "Value regenerated" );
 
+		$curTTL = null;
+		$v = $cache->get( $key, $curTTL );
+		$this->assertLessThanOrEqual( 20, $curTTL, 'Current TTL between 19-20 (overriden)' );
+		$this->assertGreaterThanOrEqual( 19, $curTTL, 'Current TTL between 19-20 (overriden)' );
+
 		$wasSet = 0;
 		$v = $cache->getWithSetCallback( $key, $func, 30, array(), array( 'lockTSE' => 5 ) );
 		$this->assertEquals( $v, $value );
-- 
2.20.1