[Cache] Prevent stampede at warmup using apcu_entry() for locking

symfony · nicolas-grekas · Apr 23, 2018 · Jun 14, 2018 · 54543aea751a60a6ea7414e44b5c604450ea4e3c
commit 54543aea751a60a6ea7414e44b5c604450ea4e3c
diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -157,6 +157,14 @@ public static function createConnection($dsn, array $options = array())
         throw new InvalidArgumentException(sprintf('Unsupported DSN: %s.', $dsn));
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function get(string $key, callable $callback, float $beta = null)
+    {
+        return $this->doGet($this, $key, $callback, $beta ?? 1.0, '' !== $this->namespace ? $this->getId($key) : null);
+    }
+
     /**
      * {@inheritdoc}
      */

diff --git a/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php b/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php
@@ -94,7 +94,7 @@ function (CacheItemInterface $innerItem, array $item) {
     public function get(string $key, callable $callback, float $beta = null)
     {
         if (!$this->pool instanceof CacheInterface) {
-            return $this->doGet($this, $key, $callback, $beta ?? 1.0);
+            return $this->doGet($this, $key, $callback, $beta ?? 1.0, $this->namespaceLen ? $this->getId($key) : null);
         }
 
         return $this->pool->get($this->getId($key), function ($innerItem) use ($key, $callback) {

diff --git a/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php b/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php
@@ -35,6 +35,7 @@ class TagAwareAdapter implements CacheInterface, TagAwareAdapterInterface, Prune
     private $setCacheItemTags;
     private $getTagsByKey;
     private $invalidateTags;
+    private $getId;
     private $tags;
     private $knownTagVersions = array();
     private $knownTagVersionsTtl;
@@ -105,6 +106,13 @@ function (AdapterInterface $tagsAdapter, array $tags) {
             null,
             CacheItem::class
         );
+        $this->getId = \Closure::bind(
+            function (AbstractAdapter $pool, $key) {
+                return $pool->getId($key);
+            },
+            null,
+            AbstractAdapter::class
+        );
     }
 
     /**
@@ -150,6 +158,22 @@ public function invalidateTags(array $tags)
         return $ok;
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function get(string $key, callable $callback, float $beta = null)
+    {
+        if ($this->pool instanceof AbstractAdapter) {
+            $id = ($this->getId)($this->pool, $key);
+        } elseif ($this->pool instanceof ProxyAdapter) {
+            $id = ((array) $this->pool)["\0Symfony\\Component\\Cache\\Adapter\\ProxyAdapter\0namespace"].$key;
+        } else {
+            $id = null;
+        }
+
+        return $this->doGet($this, $key, $callback, $beta ?? 1.0, $id !== $key ? $id : null);
+    }
+
     /**
      * {@inheritdoc}
      */

diff --git a/src/Symfony/Component/Cache/CHANGELOG.md b/src/Symfony/Component/Cache/CHANGELOG.md
@@ -5,6 +5,7 @@ CHANGELOG
 -----
 
  * added `CacheInterface`, which provides stampede protection via probabilistic early expiration and should become the preferred way to use a cache
+ * added warmup-time stampede protection using `apcu_entry()` for locking when available
  * added sub-second expiry accuracy for backends that support it
  * throw `LogicException` when `CacheItem::tag()` is called on an item coming from a non tag-aware pool
  * deprecated `CacheItem::getPreviousTags()`, use `CacheItem::getMetadata()` instead

diff --git a/src/Symfony/Component/Cache/Traits/GetTrait.php b/src/Symfony/Component/Cache/Traits/GetTrait.php
@@ -34,7 +34,7 @@ public function get(string $key, callable $callback, float $beta = null)
         return $this->doGet($this, $key, $callback, $beta ?? 1.0);
     }
 
-    private function doGet(CacheItemPoolInterface $pool, string $key, callable $callback, float $beta)
+    private function doGet(CacheItemPoolInterface $pool, string $key, callable $callback, float $beta, string $lockId = null)
     {
         $t = 0;
         $item = $pool->getItem($key);
@@ -64,6 +64,7 @@ private function doGet(CacheItemPoolInterface $pool, string $key, callable $call
         }
 
         static $save = null;
+        static $useApcu = null;
 
         if (null === $save) {
             $save = \Closure::bind(
@@ -81,6 +82,26 @@ function (CacheItemPoolInterface $pool, CacheItemInterface $item, $value, float
             );
         }
 
-        return $save($pool, $item, $callback($item), $t);
+        if (null === $lockId || !$useApcu = $useApcu ?? \function_exists('apcu_entry') && ini_get('apc.enabled') && ('cli' !== \PHP_SAPI || ini_get('apc.enable_cli'))) {
+            return $save($pool, $item, $callback($item), $t);
+        }
+
+        $t = $t ?: microtime(true);
+        $lockId = ':'.$lockId;
+        $isHit = true;
+        $value = apcu_entry($lockId, function () use ($callback, $item, &$isHit) {
+            $isHit = false;
+
+            return $callback($item);
+        }, 2);
+
+        if (!$isHit) {
+            $save($pool, $item, $value, $t);
+            // give some time to concurrent processes to get the value from APCu
+            usleep(min(300000, (microtime(true) - $t) * 150000));
+            apcu_delete($lockId);
+        }
+
+        return $value;
     }
 }