Allow GC of arguments during microtask execution (#60)

Author: Nevay

src/EventLoop/Internal/AbstractDriver.php

@@ -418,7 +418,8 @@ private function invokeMicrotasks(): void
             [$callback, $args] = $this->microtaskQueue->dequeue();
 
             try {
-                $callback(...$args);
+                // Clear $args to allow garbage collection
+                $callback(...$args, ...($args = []));
             } catch (\Throwable $exception) {
                 $this->error($callback, $exception);
             } finally {

test/Driver/DriverTest.php

@@ -1387,6 +1387,24 @@ public function testMicrotaskExecutedImmediatelyAfterCallback(): void
         });
     }
 
+    public function testMicrotaskExecutionDoesNotKeepReferenceToArgs(): void
+    {
+        $this->expectOutputString('123');
+
+        $this->loop->queue(function (object $object): void {
+            print 1;
+            unset($object);
+            print 3;
+        }, new class () {
+            public function __destruct()
+            {
+                print 2;
+            }
+        });
+
+        $this->loop->run();
+    }
+
     public function testMicrotaskThrowingStillExecutesNextMicrotask(): void
     {
         $exception = new \Exception();