Fix memory leak on flush method for TaggableStore

src/Illuminate/Cache/RedisTaggedCache.php

@@ -126,4 +126,14 @@ public function flushStale()
 
         return true;
     }
+
+    protected function onKeyWritten(string $key): void
+    {
+        // No need to do anything as the Redis store manages the entry list internally.
+    }
+
+    protected function onKeyForgotten(string $key): void
+    {
+        // No need to do anything as the Redis store manages the entry list internally.
+    }
 }

src/Illuminate/Cache/TaggedCache.php

@@ -2,6 +2,8 @@
 
 namespace Illuminate\Cache;
 
+use Illuminate\Cache\Events\KeyForgotten;
+use Illuminate\Cache\Events\KeyWritten;
 use Illuminate\Contracts\Cache\Store;
 
 class TaggedCache extends Repository
@@ -78,6 +80,10 @@ public function decrement($key, $value = 1)
      */
     public function flush()
     {
+        foreach ($this->getItemKeys() as $key) {
+            $this->store->forget($key);
+        }
+        $this->store->forget($this->getMetadataKey());
         $this->tags->reset();
 
         return true;
@@ -110,9 +116,61 @@ public function taggedItemKey($key)
      */
     protected function event($event)
     {
+        $itemKey = $this->itemKey($event->key);
+        if ($itemKey !== $this->getMetadataKey()) {
+            if ($event instanceof KeyWritten) {
+                $this->onKeyWritten($itemKey);
+            } elseif ($event instanceof KeyForgotten) {
+                $this->onKeyForgotten($itemKey);
+            }
+        }
         parent::event($event->setTags($this->tags->getNames()));
     }
 
+    protected function onKeyWritten(string $key): void
+    {
+        $itemKeys = $this->getItemKeys();
+        if (! in_array($key, $itemKeys)) {
+            $itemKeys[] = $key;
+            $this->putItemKeys($itemKeys);
+        }
+    }
+
+    protected function onKeyForgotten(string $key): void
+    {
+        $itemKeys = $this->getItemKeys();
+        if (in_array($key, $itemKeys)) {
+            $itemKeys = array_values(
+                array_filter($itemKeys, function ($k) use ($key) {
+                    return $k !== $key;
+                })
+            );
+            $this->putItemKeys($itemKeys);
+        }
+    }
+
+    private function getMetadataKey(): string
+    {
+        return $this->itemKey('meta:entries');
+    }
+
+    private function getItemKeys(): array
+    {
+        $metadataKey = $this->getMetadataKey();
+        $keys = $this->store->get($metadataKey);
+        if (! is_array($keys)) {
+            $keys = [];
+        }
+
+        return $keys;
+    }
+
+    private function putItemKeys(array $keys): void
+    {
+        $metadataKey = $this->getMetadataKey();
+        $this->store->forever($metadataKey, $keys);
+    }
+
     /**
      * Get the tag set instance.
      *

tests/Cache/CacheTaggedCacheTest.php

@@ -203,6 +203,22 @@ public function testTagsCacheForever()
         $this->assertSame('bar', $store->tags($tags)->get('foo'));
     }
 
+    public function testFlushFunctionDoesntLeakMemory()
+    {
+        $store = new ArrayStore;
+        $tags = ['bop'];
+        $before = memory_get_usage(true);
+        // Store a 5MB cache value then flush it 100 times, then verify the overall memory usage did not increase
+        for ($i = 0; $i < 100; $i++) {
+            $key = str_replace('.', '', uniqid());
+            $value = bin2hex(random_bytes(1024 * 5));
+            $store->tags($tags)->forever($key, $value);
+            $store->tags($tags)->flush();
+        }
+        $after = memory_get_usage(true);
+        $this->assertSame($before, $after);
+    }
+
     private function getTestCacheStoreWithTagValues(): ArrayStore
     {
         $store = new ArrayStore;