From b2249f93c0ec3732b7110d727d51cebdf953247b Mon Sep 17 00:00:00 2001
From: "Dylan K. Taylor" <odigiman@gmail.com>
Date: Wed, 8 Jul 2020 11:02:21 +0100
Subject: [PATCH] TaskHandler: bail if given a task that already has a handler
 This fixes undefined behaviour when scheduling the same task twice. This is
 usually accidental and almost never desirable. Note that this still allows a
 task to be scheduled again after it has been cancelled; it only disallows
 scheduling a task multiple times concurrently.

This commit will probably break MyPlot and other plugins that have
self-scheduling tasks, but as far as I can tell those use-cases should
be replaced with self-cancelling repeating tasks anyway.
---
 src/pocketmine/scheduler/TaskHandler.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/pocketmine/scheduler/TaskHandler.php b/src/pocketmine/scheduler/TaskHandler.php
index ddecf16eb..04b5f1a42 100644
--- a/src/pocketmine/scheduler/TaskHandler.php
+++ b/src/pocketmine/scheduler/TaskHandler.php
@@ -55,6 +55,9 @@ class TaskHandler{
 	private $ownerName;
 
 	public function __construct(Task $task, int $taskId, int $delay = -1, int $period = -1, ?string $ownerName = null){
+		if($task->getHandler() !== null){
+			throw new \InvalidArgumentException("Cannot assign multiple handlers to the same task");
+		}
 		$this->task = $task;
 		$this->taskId = $taskId;
 		$this->delay = $delay;