only set a new random seed if _the last_ Generator gets destruct'ed

src/Generator.php

@@ -560,6 +560,13 @@ class Generator
 
     private $container;
 
+    /**
+     * In order to prevent resetting the seed while another Generator instance is still alive, we keep track of the
+     * total, global number of Generators being "active". Incremented in __construct, decremented in __destruct.
+     * This is necessary, because __destruct modifies global state (`mt_srand`).
+     */
+    private static int $generatorsAlive = 0;
+
     /**
      * @var UniqueGenerator
      */
@@ -568,6 +575,7 @@ class Generator
     public function __construct(ContainerInterface $container = null)
     {
         $this->container = $container ?: Container\ContainerBuilder::withDefaultExtensions()->build();
+        ++self::$generatorsAlive;
     }
 
     /**
@@ -963,7 +971,9 @@ public function __call($method, $attributes)
 
     public function __destruct()
     {
-        $this->seed();
+        if ((--self::$generatorsAlive) <= 0) {
+            $this->seed();
+        }
     }
 
     public function __wakeup()

test/GeneratorTest.php

@@ -11,6 +11,7 @@
 use Faker\Extension\BloodExtension;
 use Faker\Extension\ExtensionNotFound;
 use Faker\Extension\FileExtension;
+use Faker\Factory;
 use Faker\Generator;
 use Faker\Provider;
 use Faker\UniqueGenerator;
@@ -327,4 +328,24 @@ public function word(): string
 
         $uniqueGenerator->word();
     }
+
+    public function testDestructingOldGeneratorDoesNotResetTheSeed(): void
+    {
+        $faker = Factory::create('en_US');
+        $faker->seed(1);
+
+        $expected1 = $faker->numberBetween(1000, 10000);
+        $expected2 = $faker->numberBetween(1000, 10000);
+        $faker = null;
+
+        for ($i = 0; $i < 3; ++$i) {
+            $faker = Factory::create('en_US');
+            $faker->seed(1);
+            self::assertSame($expected1, $faker->numberBetween(1000, 10000));
+
+            gc_collect_cycles();
+
+            self::assertSame($expected2, $faker->numberBetween(1000, 10000));
+        }
+    }
 }