Destructable performance wins

commerce_stripe.services.yml

services:
  commerce_stripe.order_events_subscriber:
    class: Drupal\commerce_stripe\EventSubscriber\OrderEventsSubscriber
    arguments: ['@entity_type.manager']
    tags:
      - { name: needs_destruction }
      - { name: event_subscriber }

OrderEventsSubscriber.php

<?php

namespace Drupal\commerce_stripe\EventSubscriber;

use Drupal\commerce_order\Event\OrderEvent;
use Drupal\commerce_order\Event\OrderEvents;
use Drupal\commerce_price\Calculator;
use Drupal\commerce_price\Price;
use Drupal\commerce_stripe\Plugin\Commerce\PaymentGateway\StripeInterface;
use Drupal\Core\DestructableInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Stripe\Error\Base as StripeError;
use Stripe\PaymentIntent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Subscribers to order events for the Stripe integration.
 */
class OrderEventsSubscriber implements EventSubscriberInterface, DestructableInterface {

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * The intent IDs that need updating.
   *
   * @var int[]
   */
  protected $updateList = [];

  /**
   * Constructs a new OrderEventsSubscriber object.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager) {
    $this->entityTypeManager = $entity_type_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    return [
      OrderEvents::ORDER_UPDATE => 'onOrderUpdate',
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function destruct() {
    foreach ($this->updateList as $intent_id => $amount) {
      try {
        PaymentIntent::update($intent_id, ['amount' => $amount]);
      }
      catch (StripeError $e) {
        // Allow sync errors to silently fail.
      }
    }
  }

  /**
   * Ensures the Stripe payment intent is up to date.
   *
   * @param \Drupal\commerce_order\Event\OrderEvent $event
   *   The event.
   */
  public function onOrderUpdate(OrderEvent $event) {
    $order = $event->getOrder();
    $gateway = $order->get('payment_gateway');
    if ($gateway->isEmpty()) {
      return;
    }
    $plugin = $gateway->entity->getPlugin();
    if (!$plugin instanceof StripeInterface) {
      return;
    }
    $intent_id = $order->getData('stripe_intent');
    if ($intent_id !== NULL) {
      $amount = $this->toMinorUnits($order->getTotalPrice());
      $this->updateList[$intent_id] = $amount;
    }
  }

  /**
   * Converts the given amount to its minor units.
   *
   * For example, 9.99 USD becomes 999.
   *
   * @todo Remove after https://www.drupal.org/node/2944281 is fixed.
   *
   * @param \Drupal\commerce_price\Price $amount
   *   The amount.
   *
   * @return int
   *   The amount in minor units, as an integer.
   */
  private function toMinorUnits(Price $amount) {
    $currency_storage = $this->entityTypeManager->getStorage('commerce_currency');
    /** @var \Drupal\commerce_price\Entity\CurrencyInterface $currency */
    $currency = $currency_storage->load($amount->getCurrencyCode());
    $fraction_digits = $currency->getFractionDigits();
    $number = $amount->getNumber();
    if ($fraction_digits > 0) {
      $number = Calculator::multiply($number, pow(10, $fraction_digits));
    }

    return round($number, 0);
  }

}