Tasks and asynchronous work

Use the plugin scheduler instead of blocking a command or event handler. Keep the returned TaskHandle when later code may need to cancel the task.

Repeating timer

$handle = $this->context()->scheduler()->delayedRepeating(
    delayTicks: 20,
    periodTicks: 20,
    callback: function (): void {
        foreach ($this->context()->server()->getOnlinePlayers() as $player) {
            $player->sendPopup('The arena round is still running.');
        }
    },
);

Async work

Async tasks must receive bounded serializable input. They must not retain live players, worlds, inventories, entity controllers, or the plugin context. Return an AsyncTaskValue, then apply the result through a scheduled server-thread callback after rechecking that the target player or world is still available.

Handle TaskRejectedException and async failures explicitly. Cancellation does not make already-running external work transactional.