checkpoint example

private readonly ClockInterface $clock = new Clock(),
        private ?CheckpointInterface $checkpoint = null,
    ) {
        $this->waitUntil = new \DateTimeImmutable('@0');
    }

    /** * @return \Generator<MessageContext, object> */
    public function getMessages(): \Generator
    {
        $checkpoint = $this->checkpoint();

        if ($this->schedule?->shouldRestart()) {
            unset($this->triggerHeap);
            $this->waitUntil = new \DateTimeImmutable('@0');
            $this->schedule->setRestart(false);
        }

        if (!$this->waitUntil
            || $this->waitUntil > ($now = $this->clock->now())
            || !$checkpoint->acquire($now)
        ) {