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

nicolas-grekas · nicolas-grekas · commit ec2b4c02e582 · 2018-04-24T16:34:50.000+02:00
diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -145,6 +145,14 @@ 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
@@ -80,7 +80,7 @@ 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 TagAwareAdapterInterface, TaggableCacheInterfac
     private $setCacheItemTags;
     private $getTagsByKey;
     private $invalidateTags;
+    private $getId;
     private $tags;
 
     public function __construct(AdapterInterface $itemsPool, AdapterInterface $tagsPool = null)
@@ -103,6 +104,13 @@ function (AdapterInterface $tagsAdapter, array $tags) {
             null,
             CacheItem::class
         );
+        $this->getId = \Closure::bind(
+            function (AbstractAdapter $pool, $key) {
+                return $pool->getId($key);
+            },
+            null,
+            AbstractAdapter::class
+        );
     }
 
     /**
@@ -120,6 +128,22 @@ public function invalidateTags(array $tags)
         return $f($this->tags, $tags);
     }
 
+    /**
+     * {@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/Tests/Adapter/AdapterTestCase.php b/src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php
@@ -78,9 +78,9 @@ public function testGetStats()
 
         $expected = array(
             CacheItem::STATS_CTIME => 1.0,
-            CacheItem::STATS_EXPIRY => 9 + time(),
+            CacheItem::STATS_EXPIRY => 8.5 + time(),
         );
-        $this->assertSame($expected, $item->getStats());
+        $this->assertEquals($expected, $item->getStats(), 'Item stats should be stored alongside with its value.', 0.5);
     }
 
     public function testDefaultLifeTime()
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(
@@ -80,7 +81,30 @@ function (CacheItemPoolInterface $pool, CacheItemInterface $item, $value, float
                 CacheItem::class
             );
         }
+        if (null === $useApcu) {
+            $useApcu = \function_exists('apcu_entry') && ini_get('apc.enabled') && ('cli' !== \PHP_SAPI || ini_get('apc.enable_cli'));
+        }
+
+        if (null === $lockId || !$useApcu) {
+            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 concurrent processes 15% of the computation time to retrieve the value from APCu, up to 300ms
+            usleep(min(300000, 150000 * (microtime(true) - $t)));
+            apcu_delete($lockId);
+        }
 
-        return $save($pool, $item, $callback($item), $t);
+        return $value;
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -80,7 +80,7 @@ function (CacheItemInterface $innerItem, array $item) {`
`80`	`80`	`public function get(string $key, callable $callback, float $beta = null)`
`81`	`81`	`{`
`82`	`82`	`if (!$this->pool instanceof CacheInterface) {`
`83`		`- return $this->doGet($this, $key, $callback, $beta ?? 1.0);`
	`83`	`+ return $this->doGet($this, $key, $callback, $beta ?? 1.0, $this->namespaceLen ? $this->getId($key) : null);`
`84`	`84`	`}`
`85`	`85`
`86`	`86`	`return $this->pool->get($this->getId($key), function ($innerItem) use ($key, $callback) {`