feature #35362 [Cache] Add LRU + max-lifetime capabilities to ArrayCache (nicolas-grekas)

This PR was merged into the 5.1-dev branch.

Discussion
----------

[Cache] Add LRU + max-lifetime capabilities to ArrayCache

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix https://github.com/orgs/symfony/projects/1#card-30686676
| License       | MIT
| Doc PR        | -

In https://github.com/symfony/symfony/pull/32294#issuecomment-508067745, @andrerom writes:

> if you plan to expose use of ArrayAdapter to a wider audience you should probably also add the following features to it:
> - max item limit to avoid reaching memory limits
> - own (very low, like default 100-500ms) TTL for in-memory caching, as it's in practice stale data when used in concurrent scenarios
>
> If you want to be advance you can also:
>
> - keep track of use, and evict cache items based on that using LFU when reaching limit
> - in-memory cache is domain & project specific in terms of how long it's somewhat "safe" to keep items in memory, so either describe when to use and not use on a per pool term, or allow use of pool to pass in flags to opt out of in-memory cache for cases developer knows it should be ignored

This PR implements these suggestions, via two new constructor arguments: `$maxLifetime` and `$maxItems`.

In Yaml:
```yaml
services:
    app.lru150_cache:
        parent: cache.adapter.array
        arguments:
            $maxItems: 150
            $maxLifetime: 0.150

framework:
    cache:
        pools:
            my_chained_pool:
                adapters:
                  - app.lru150_cache
                  - cache.adapter.filesystem
```

This configuration adds a local memory cache that keeps max 150 elements for 150ms on top of a filesystem cache.

/cc @lyrixx since you were also interested in it.

Commits
-------

48a5d5e8a9 [Cache] Add LRU + max-lifetime capabilities to ArrayCache

src/Symfony/Component/Cache/Adapter/ArrayAdapter.php

@@ -15,10 +15,15 @@ use Psr\Cache\CacheItemInterface;
 use Psr\Log\LoggerAwareInterface;
 use Psr\Log\LoggerAwareTrait;
 use Symfony\Component\Cache\CacheItem;
+use Symfony\Component\Cache\Exception\InvalidArgumentException;
 use Symfony\Component\Cache\ResettableInterface;
 use Symfony\Contracts\Cache\CacheInterface;
 
 /**
+ * An in-memory cache storage.
+ *
+ * Acts as a least-recently-used (LRU) storage when configured with a maximum number of items.
+ *
  * @author Nicolas Grekas <p@tchwork.com>
  */
 class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInterface, ResettableInterface
@@ -29,13 +34,25 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
     private $values = [];
     private $expiries = [];
     private $createCacheItem;
+    private $maxLifetime;
+    private $maxItems;
 
     /**
      * @param bool $storeSerialized Disabling serialization can lead to cache corruptions when storing mutable values but increases performance otherwise
      */
-    public function __construct(int $defaultLifetime = 0, bool $storeSerialized = true)
+    public function __construct(int $defaultLifetime = 0, bool $storeSerialized = true, int $maxLifetime = 0, int $maxItems = 0)
     {
+        if (0 > $maxLifetime) {
+            throw new InvalidArgumentException(sprintf('Argument $maxLifetime must be a positive integer, %d passed.', $maxLifetime));
+        }
+
+        if (0 > $maxItems) {
+            throw new InvalidArgumentException(sprintf('Argument $maxItems must be a positive integer, %d passed.', $maxItems));
+        }
+
         $this->storeSerialized = $storeSerialized;
+        $this->maxLifetime = $maxLifetime;
+        $this->maxItems = $maxItems;
         $this->createCacheItem = \Closure::bind(
             static function ($key, $value, $isHit) use ($defaultLifetime) {
                 $item = new CacheItem();
@@ -84,6 +101,13 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
     public function hasItem($key)
     {
         if (\is_string($key) && isset($this->expiries[$key]) && $this->expiries[$key] > microtime(true)) {
+            if ($this->maxItems) {
+                // Move the item last in the storage
+                $value = $this->values[$key];
+                unset($this->values[$key]);
+                $this->values[$key] = $value;
+            }
+
             return true;
         }
         CacheItem::validateKey($key);
@@ -97,7 +121,12 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
     public function getItem($key)
     {
         if (!$isHit = $this->hasItem($key)) {
-            $this->values[$key] = $value = null;
+            $value = null;
+
+            if (!$this->maxItems) {
+                // Track misses in non-LRU mode only
+                $this->values[$key] = null;
+            }
         } else {
             $value = $this->storeSerialized ? $this->unfreeze($key, $isHit) : $this->values[$key];
         }
@@ -164,7 +193,9 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
         $value = $item["\0*\0value"];
         $expiry = $item["\0*\0expiry"];
 
-        if (null !== $expiry && $expiry <= microtime(true)) {
+        $now = microtime(true);
+
+        if (null !== $expiry && $expiry <= $now) {
             $this->deleteItem($key);
 
             return true;
@@ -173,7 +204,23 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
             return false;
         }
         if (null === $expiry && 0 < $item["\0*\0defaultLifetime"]) {
-            $expiry = microtime(true) + $item["\0*\0defaultLifetime"];
+            $expiry = $item["\0*\0defaultLifetime"];
+            $expiry = $now + ($expiry > ($this->maxLifetime ?: $expiry) ? $this->maxLifetime : $expiry);
+        } elseif ($this->maxLifetime && (null === $expiry || $expiry > $now + $this->maxLifetime)) {
+            $expiry = $now + $this->maxLifetime;
+        }
+
+        if ($this->maxItems) {
+            unset($this->values[$key]);
+
+            // Iterate items and vacuum expired ones while we are at it
+            foreach ($this->values as $k => $v) {
+                if ($this->expiries[$k] > $now && \count($this->values) < $this->maxItems) {
+                    break;
+                }
+
+                unset($this->values[$k], $this->expiries[$k]);
+            }
         }
 
         $this->values[$key] = $value;
@@ -210,15 +257,21 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
     public function clear(string $prefix = '')
     {
         if ('' !== $prefix) {
+            $now = microtime(true);
+
             foreach ($this->values as $key => $value) {
-                if (0 === strpos($key, $prefix)) {
+                if (!isset($this->expiries[$key]) || $this->expiries[$key] <= $now || 0 === strpos($key, $prefix)) {
                     unset($this->values[$key], $this->expiries[$key]);
                 }
             }
-        } else {
-            $this->values = $this->expiries = [];
+
+            if ($this->values) {
+                return true;
+            }
         }
 
+        $this->values = $this->expiries = [];
+
         return true;
     }
 
@@ -258,8 +311,20 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
     {
         foreach ($keys as $i => $key) {
             if (!$isHit = isset($this->expiries[$key]) && ($this->expiries[$key] > $now || !$this->deleteItem($key))) {
-                $this->values[$key] = $value = null;
+                $value = null;
+
+                if (!$this->maxItems) {
+                    // Track misses in non-LRU mode only
+                    $this->values[$key] = null;
+                }
             } else {
+                if ($this->maxItems) {
+                    // Move the item last in the storage
+                    $value = $this->values[$key];
+                    unset($this->values[$key]);
+                    $this->values[$key] = $value;
+                }
+
                 $value = $this->storeSerialized ? $this->unfreeze($key, $isHit) : $this->values[$key];
             }
             unset($keys[$i]);
@@ -314,8 +379,12 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
                 $value = false;
             }
             if (false === $value) {
-                $this->values[$key] = $value = null;
+                $value = null;
                 $isHit = false;
+
+                if (!$this->maxItems) {
+                    $this->values[$key] = null;
+                }
             }
         }
 

src/Symfony/Component/Cache/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+5.1.0
+-----
+
+ * added max-items + LRU + max-lifetime capabilities to `ArrayCache`
+
 5.0.0
 -----
 

src/Symfony/Component/Cache/Tests/Adapter/ArrayAdapterTest.php

@@ -55,4 +55,36 @@ class ArrayAdapterTest extends AdapterTestCase
         $this->assertArrayHasKey('bar', $values);
         $this->assertNull($values['bar']);
     }
+
+    public function testMaxLifetime()
+    {
+        $cache = new ArrayAdapter(0, false, 1);
+
+        $item = $cache->getItem('foo');
+        $item->expiresAfter(2);
+        $cache->save($item->set(123));
+
+        $this->assertTrue($cache->hasItem('foo'));
+        sleep(1);
+        $this->assertFalse($cache->hasItem('foo'));
+    }
+
+    public function testMaxItems()
+    {
+        $cache = new ArrayAdapter(0, false, 0, 2);
+
+        $cache->save($cache->getItem('foo'));
+        $cache->save($cache->getItem('bar'));
+        $cache->save($cache->getItem('buz'));
+
+        $this->assertFalse($cache->hasItem('foo'));
+        $this->assertTrue($cache->hasItem('bar'));
+        $this->assertTrue($cache->hasItem('buz'));
+
+        $cache->save($cache->getItem('foo'));
+
+        $this->assertFalse($cache->hasItem('bar'));
+        $this->assertTrue($cache->hasItem('buz'));
+        $this->assertTrue($cache->hasItem('foo'));
+    }
 }