Improved performance of event calls

This change significantly reduces the amount of work done by event handlers. Instead of traversing all of the priorities and event parent chain multiple times, we reduce event handlers down to a simple list, which doesn't require any logic to iterate over.
Previously, calling an event with lots of parents costed more than an event which directly descended from Event.
In addition, we had to do a lot of usually useless work to check all priorities, when in practice, only NORMAL will be used in almost all cases.

This change makes it more cost effective to implement the feature suggested by #5678; however, it will still require additional changes.

src/event/Event.php

@@ -59,15 +59,8 @@ abstract class Event{
 
 		++self::$eventCallDepth;
 		try{
-			foreach(EventPriority::ALL as $priority){
-				$currentList = $handlerList;
-				while($currentList !== null){
-					foreach($currentList->getListenersByPriority($priority) as $registration){
-						$registration->callEvent($this);
-					}
-
-					$currentList = $currentList->getParent();
-				}
+			foreach($handlerList->getListenerList() as $registration){
+				$registration->callEvent($this);
 			}
 		}finally{
 			--self::$eventCallDepth;

src/event/HandlerList.php

@@ -31,6 +31,11 @@ class HandlerList{
 	/** @var RegisteredListener[][] */
 	private array $handlerSlots = [];
 
+	private RegisteredListenerCache $handlerCache;
+
+	/** @var RegisteredListenerCache[] */
+	private array $affectedHandlerCaches = [];
+
 	/**
 	 * @phpstan-template TEvent of Event
 	 * @phpstan-param class-string<TEvent> $class
@@ -39,6 +44,11 @@ class HandlerList{
 		private string $class,
 		private ?HandlerList $parentList
 	){
+		$this->handlerCache = new RegisteredListenerCache();
+		for($list = $this; $list !== null; $list = $list->parentList){
+			$list->affectedHandlerCaches[spl_object_id($this->handlerCache)] = $this->handlerCache;
+		}
+
 		$this->handlerSlots = array_fill_keys(EventPriority::ALL, []);
 	}
 
@@ -50,6 +60,7 @@ class HandlerList{
 			throw new \InvalidArgumentException("This listener is already registered to priority {$listener->getPriority()} of event {$this->class}");
 		}
 		$this->handlerSlots[$listener->getPriority()][spl_object_id($listener)] = $listener;
+		$this->invalidateAffectedCaches();
 	}
 
 	/**
@@ -59,6 +70,7 @@ class HandlerList{
 		foreach($listeners as $listener){
 			$this->register($listener);
 		}
+		$this->invalidateAffectedCaches();
 	}
 
 	/**
@@ -78,10 +90,12 @@ class HandlerList{
 		}elseif($object instanceof RegisteredListener){
 			unset($this->handlerSlots[$object->getPriority()][spl_object_id($object)]);
 		}
+		$this->invalidateAffectedCaches();
 	}
 
 	public function clear() : void{
 		$this->handlerSlots = array_fill_keys(EventPriority::ALL, []);
+		$this->invalidateAffectedCaches();
 	}
 
 	/**
@@ -94,4 +108,39 @@ class HandlerList{
 	public function getParent() : ?HandlerList{
 		return $this->parentList;
 	}
+
+	/**
+	 * Invalidates all known caches which might be affected by this list's contents.
+	 */
+	private function invalidateAffectedCaches() : void{
+		foreach($this->affectedHandlerCaches as $cache){
+			$cache->list = null;
+		}
+	}
+
+	/**
+	 * @return RegisteredListener[]
+	 * @phpstan-return list<RegisteredListener>
+	 */
+	public function getListenerList() : array{
+		if($this->handlerCache->list !== null){
+			return $this->handlerCache->list;
+		}
+
+		$handlerLists = [];
+		for($currentList = $this; $currentList !== null; $currentList = $currentList->parentList){
+			$handlerLists[] = $currentList;
+		}
+
+		$listeners = [];
+		foreach(EventPriority::ALL as $priority){
+			foreach($handlerLists as $currentList){
+				foreach($currentList->getListenersByPriority($priority) as $registration){
+					$listeners[] = $registration;
+				}
+			}
+		}
+
+		return $this->handlerCache->list = $listeners;
+	}
 }

src/event/RegisteredListenerCache.php

@@ -0,0 +1,35 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+ */
+
+declare(strict_types=1);
+
+namespace pocketmine\event;
+
+final class RegisteredListenerCache{
+
+	/**
+	 * List of all handlers that will be called for a particular event, ordered by execution order.
+	 *
+	 * @var RegisteredListener[]
+	 * @phpstan-var list<RegisteredListener>
+	 */
+	public ?array $list = null;
+}