TaskPluginManager.php

<?php

namespace Drupal\sitemanager\Plugin;

use Drupal\Core\Plugin\DefaultPluginManager;
use Drupal\Core\Cache\CacheBackendInterface;
use Drupal\Core\Extension\ModuleHandlerInterface;

/**
 * Provides the Task plugin plugin manager.
 */
class TaskPluginManager extends DefaultPluginManager {

  protected $settings;

  /**
   * Constructor for TaskPluginManager objects.
   *
   * @param \Traversable $namespaces
   *   An object that implements \Traversable which contains the root paths
   *   keyed by the corresponding namespace to look for plugin implementations.
   * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
   *   Cache backend instance to use.
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler to invoke the alter hook with.
   */
  public function __construct(\Traversable $namespaces, 
                              CacheBackendInterface $cache_backend, 
                              ModuleHandlerInterface $module_handler) {
    parent::__construct('Plugin/SMTaskPlugin', $namespaces, $module_handler,
                        'Drupal\sitemanager\Plugin\TaskPluginInterface',
                        'Drupal\sitemanager\Annotation\TaskPlugin');

    $this->alterInfo('sitemanager_task_plugin_info');
    $this->setCacheBackend($cache_backend, 'sitemanager_task_plugins');
  }