Sends viewer count of a double chest and it's pairs.

DoubleChestDebug.php

<?php
/**
 * @name DoubleChestDebug
 * @main muqsit\dcdcd\Main
 * @version 1.0
 * @api 3.0.0
 */
namespace muqsit\dcdcd {

    use pocketmine\plugin\PluginBase;
    use pocketmine\event\inventory\InventoryOpenEvent;
    use pocketmine\event\Listener;
    use pocketmine\inventory\DoubleChestInventory;
    use pocketmine\scheduler\Task;

    class Main extends PluginBase implements Listener {

        public function onEnable() : void
        {
            $this->getServer()->getPluginManager()->registerEvents($this, $this);
        }

        public function onInventoryOpen(InventoryOpenEvent $event) : void
        {
            $inventory = $event->getInventory();
            if ($inventory instanceof DoubleChestInventory) {
                $this->getScheduler()->scheduleRepeatingTask(new ViewerCountTask($this, $inventory), 1);
            }
        }
    }

    class ViewerCountTask extends Task {

        /** @var Main */
        private $plugin;

        /** @var DoubleChestInventory  */
        private $inventory;

        public function __construct(Main $plugin, DoubleChestInventory $inventory)
        {
            $this->plugin = $plugin;
            $this->inventory = $inventory;
        }

        public function onRun(int $tick) : void
        {
            $viewers = count($this->inventory->getViewers());
            $viewers_l = count($this->inventory->getLeftSide()->getViewers());
            $viewers_r = count($this->inventory->getRightSide()->getViewers());

            var_dump([
                "viewers" => $viewers,
                "viewers_l" => $viewers_l,
                "viewers_r" => $viewers_r
            ]);

            if ($viewers === 0 && $viewers_l === 0 && $viewers_r === 0) {
                $this->plugin->getScheduler()->cancelTask($this->getTaskId());
                echo "Dropped " . get_class($this) . " due to 0 viewers" . PHP_EOL;
            }
        }
    }
}