Proof of concept for abusing yield as sleep

YieldTask.php

<?php
namespace SOFe\YieldTask;
use pocketmine\plugin\Plugin;
use pocketmine\scheduler\PluginTask;
class YieldTask extends PluginTask{
  const UNIT_TICKS = 1;
  const UNIT_SECONDS = 20;
  const UNIT_MINUTES = 1200;
  private $generator;
  private $factor;
  public function __construct(Plugin $owner, $generator, int $unit = self::UNIT_SECONDS){
    if(is_callable($generator)) $generator = $generator();
    if(!($generator instanceof \Generator)) throw new \InvalidArgumentException;
    parent::__construct($owner);
    $this->generator = $generator;
    $this->factor = $unit;
    $this->owner->getServer()->getScheduler()->scheduleDelayedTask($this, $this->generator->current() * $this->factor);
  }
  public function onRun(int $tick){
    $this->generator->next();
    $this->owner->getServer()->getScheduler()->scheduleDelayedTask($this, $this->generator->current() * $this->factor);
  }
}

YieldTaskTest.php

<?php
namespace SOFe\YieldTaskTest;
use pocketmine\plugin\PluginBase;
use SOFe\YieldTask\YieldTask;
class YieldTaskTest extends PluginBase{
  public function onCommand(CommandSender $sender, Command $command, string $label, array $args) : bool{
    new YieldTask($this, function() use($sender){
      $sender->sendMessage("10 seconds left");
      yield 1;
      $sender->sendMessage("9 seconds left");
      yield 4;
      $sender->sendMessage("5 seconds left");
      yield 5;
      $sender->sendMessage("Time's up!");
    }, YieldTask::UNIT_SECONDS);
    return true;
  }
}

Really neat, this could be used in countless ways.