如何释放线程中使用的Symfony（PHP）内核？

在PHP7.0.2中，开发一个symfony2命令，在该命令中创建两级线程（fork）

有一个容器类实例化MyWorker类（扩展自Worker），并为$workers数组中的每个MyWorker元素调用start（）函数

通过调用MyWorker的函数start（），函数运行时创建了一个Symfony实例，在存储库中搜索数据，每个MyWorker创建了属于MyThread类的5个子函数，并称为调用run函数的函数start（）

在MyThread的run函数中，Symfony再次被实例化（我没有找到通过父实例实现的方法）

问题在于，当反复调用process（）函数（超过200次）时，会生成以下内存错误：

mmap () failed: [12] Can not allocate memory. Fatal error: Out of memory (allocated 2820669440) (tried to allocate 32768 bytes) in /srv/www/leadpro.com/current/vendor/symfony/symfony/src/Symfony/Component/Debug/Exception/OutOfMemoryException.php on line 1

我假设必须生成错误，因为symfony实例没有在worker和线程中释放

如果有人能提出解决方案，我将不胜感激

    class MyWorker extends \Worker
    {
        protected $container;
        protected $document_manager;    
        protected $id;  

        public function __construct ( $param )
        {
            $id = $param['id'];
            //... Set other parameters
        }


        public function setDoctrineManagerInWorker()
        {
            //Set require Autoload and AppKernel
            require_once __DIR__.'/../../../../app/autoload.php';
            require_once __DIR__.'/../../../../app/AppKernel.php';

            //Creating a new AppKernel with the given environment
            $kernel = new \AppKernel( 'dev', 1 );
            //Loading the Cache and Classes
            $kernel->loadClassCache();
            $kernel->boot();

            //Set container
            $container = $kernel->getContainer();

            //Set document manager
            $document_manager = $kernel->getContainer()->get('doctrine')->getManager();
        }


        public function run()
        {
            $this->setDoctrineManagerInWorker();        

            //... Aqui se aplica la logica para acceder a los repositorios

            $worker = $this->document_manager->getRepository('MyBundle:Worker')->find( $this->getId() );        

            //...

            for ( $i = 0; $i < 5; $i++ )
            {
               $thread = new MyThread( $param );
               $thread->start();
               $thread->join();
            }
        }
    }

    class MyThread extends \Thread
    {
        protected $container;
        protected $document_manager;    

        public function __construct ( $param )
        {
            //... Set parameters
        }

        public function setDoctrineManagerInThread()
        {
            //Set require Autoload and AppKernel
            require_once __DIR__.'/../../../../app/autoload.php';
            require_once __DIR__.'/../../../../app/AppKernel.php';

            $kernel = new \AppKernel( 'dev', 1 );
            //Loading the Cache and Classes
            $kernel->loadClassCache();
            $kernel->boot();
            //Set container
            $this->container = $kernel->getContainer();
            //Set document manager
            $this->document_manager= $kernel->getContainer()->get('doctrine_mongodb')->getManager();
        }

        public function run()
        {
            $this->setDoctrineManagerInThread();

            //... Logical processing of repositories
            $thread = $this->document_manager->getRepository('MyBundle:Thread')->findAll();
            //...
        }
    }

mmap () failed: [12] Can not allocate memory. Fatal error: Out of memory (allocated 2820669440) (tried to allocate 32768 bytes) in /srv/www/leadpro.com/current/vendor/symfony/symfony/src/Symfony/Component/Debug/Exception/OutOfMemoryException.php on line 1