Adding support for native WeakReferences

PHP 7.4 adds native support for WeakReferences.
There will be no need for the weakref extension (that was incompatible with PHP 7.3).

This PR adds support for these new Weakrefences.

Author: moufmouf

src/NativeWeakrefObjectStorage.php

@@ -0,0 +1,107 @@
+<?php
+declare(strict_types=1);
+
+/*
+ Copyright (C) 2006-2014 David Négrier - THE CODING MACHINE
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+namespace TheCodingMachine\TDBM;
+
+use WeakReference;
+
+/**
+ * The NativeWeakrefObjectStorage class is used to reference all beans that have been fetched from the database.
+ * If a bean is requested twice from TDBM, the NativeWeakrefObjectStorage is used to "cache" the bean.
+ * Unlike the StandardObjectStorage, the NativeWeakrefObjectStorage manages memory in a clever way, using WeakReference.
+ * WeakReference have been added in PHP 7.4.
+ *
+ * @author David Negrier
+ */
+class NativeWeakrefObjectStorage implements ObjectStorageInterface
+{
+    /**
+     * An array of fetched object, accessible via table name and primary key.
+     * If the primary key is split on several columns, access is done by an array of columns, serialized.
+     *
+     * @var WeakReference[][]
+     */
+    private $objects = array();
+
+    /**
+     * Every 10000 set in the dataset, we perform a cleanup to ensure the WeakRef instances
+     * are removed if they are no more valid.
+     * This is to avoid having memory used by dangling WeakRef instances.
+     *
+     * @var int
+     */
+    private $garbageCollectorCount = 0;
+
+    /**
+     * Sets an object in the storage.
+     *
+     * @param string $tableName
+     * @param string|int $id
+     * @param DbRow  $dbRow
+     */
+    public function set(string $tableName, $id, DbRow $dbRow): void
+    {
+        $this->objects[$tableName][$id] = WeakReference::create($dbRow);
+        ++$this->garbageCollectorCount;
+        if ($this->garbageCollectorCount === 10000) {
+            $this->garbageCollectorCount = 0;
+            $this->cleanupDanglingWeakRefs();
+        }
+    }
+
+    /**
+     * Returns an object from the storage (or null if no object is set).
+     *
+     * @param string $tableName
+     * @param string|int $id
+     *
+     * @return DbRow|null
+     */
+    public function get(string $tableName, $id) : ?DbRow
+    {
+        if (isset($this->objects[$tableName][$id])) {
+            return $this->objects[$tableName][$id]->get();
+        }
+        return null;
+    }
+
+    /**
+     * Removes an object from the storage.
+     *
+     * @param string $tableName
+     * @param string|int $id
+     */
+    public function remove(string $tableName, $id): void
+    {
+        unset($this->objects[$tableName][$id]);
+    }
+
+    private function cleanupDanglingWeakRefs(): void
+    {
+        foreach ($this->objects as $tableName => $table) {
+            foreach ($table as $id => $obj) {
+                if ($obj->valid() === false) {
+                    unset($this->objects[$tableName][$id]);
+                }
+            }
+        }
+    }
+}

src/TDBMService.php

@@ -21,6 +21,7 @@
 
 namespace TheCodingMachine\TDBM;
 
+use function class_exists;
 use Doctrine\Common\Cache\Cache;
 use Doctrine\Common\Cache\ClearableCache;
 use Doctrine\Common\Cache\VoidCache;
@@ -46,7 +47,7 @@
 use Psr\Log\LoggerInterface;
 use Psr\Log\LogLevel;
 use Psr\Log\NullLogger;
-use function var_export;
+use WeakReference;
 
 /**
  * The TDBMService class is the main TDBM class. It provides methods to retrieve TDBMObject instances
@@ -179,7 +180,9 @@ class TDBMService
      */
     public function __construct(ConfigurationInterface $configuration)
     {
-        if (extension_loaded('weakref')) {
+        if (class_exists(WeakReference::class)) {
+            $this->objectStorage = new NativeWeakrefObjectStorage();
+        } elseif (extension_loaded('weakref')) {
             $this->objectStorage = new WeakrefObjectStorage();
         } else {
             $this->objectStorage = new StandardObjectStorage();

src/WeakrefObjectStorage.php

@@ -26,7 +26,9 @@
  * If a bean is requested twice from TDBM, the WeakrefObjectStorage is used to "cache" the bean.
  * Unlike the StandardObjectStorage, the WeakrefObjectStorage manages memory in a clever way, using the weakref
  * PHP extension. It is used if the "weakref" extension is available.
- * Otherwise, the StandardObjectStorage is used instead.
+ * Otherwise, the StandardObjectStorage or NativeWeakrefObjectStorage (in PHP 7.4+) is used instead.
+ *
+ * Note: the weakref extension is available until PHP 7.2, but not available in PHP 7.3+
  *
  * @author David Negrier
  */