CachePreWarmer.php

<?php

namespace Drupal\Core\PreWarm;

use Drupal\Core\DependencyInjection\ClassResolverInterface;
// cspell:ignore ABCDEF FCDABE BEDAFC

/**
 * Prewarms caches for services that implement PreWarmableInterface.
 *
 * Takes a list of prewarmable services and prewarms them at random.
 * Randomization is used because whenever two or more requests are building
 * caches, the most benefit is gained by minimizing duplication. For example
 * two requests rely on the same six services but these services are requested
 * at different times, one request builds caches for the other and vice versa.
 *
 * No randomization:
 *
 * ABCDEF
 * ABCDEF
 *
 * Randomization:
 *
 * ABCDEF
 * FCDABE
 *
 * Randomization and three requests:
 *
 * ABCDEF
 * FCDABE
 * BEDAFC
 *
 * @internal
 *
 * @see Drupal\Core\PreWarm\PreWarmableInterface
 * @see Drupal\Core\DrupalKernel::handle()
 * @see Drupal\Core\LockBackendAbstract::wait()
 * @see Drupal\Core\Routing\RouteProvider::preLoadRoutes()
 */
class CachePreWarmer implements CachePreWarmerInterface {
    
    /**
     * Whether to prewarm caches at the end of the request.
     */
    protected bool $needsPreWarming = FALSE;
    public function __construct(ClassResolverInterface $classResolver, array $serviceIds) {
        // Ensure the serviceId order is random to reduce chances of conflicts.
        shuffle($this->serviceIds);
    }
    
    /**
     * {@inheritdoc}
     */
    public function preWarmOneCache() : bool {
        $candidate = array_pop($this->serviceIds);
        if ($candidate === NULL) {
            return FALSE;
        }
        $service = $this->classResolver
            ->getInstanceFromDefinition($candidate);
        $service->preWarm();
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function preWarmAllCaches() : bool {
        $prewarmed = FALSE;
        while ($this->preWarmOneCache()) {
            $prewarmed = TRUE;
        }
        return $prewarmed;
    }

}