From 4724195791f3c8dee6d51677438d507a19b3a1a8 Mon Sep 17 00:00:00 2001
From: "Dylan K. Taylor" <dktapps@pmmp.io>
Date: Wed, 5 Apr 2023 23:02:28 +0100
Subject: [PATCH] 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                   | 11 ++----
 src/event/HandlerList.php             | 49 +++++++++++++++++++++++++++
 src/event/RegisteredListenerCache.php | 35 +++++++++++++++++++
 3 files changed, 86 insertions(+), 9 deletions(-)
 create mode 100644 src/event/RegisteredListenerCache.php

diff --git a/src/event/Event.php b/src/event/Event.php
index df0f6bb03..1ae7bb96f 100644
--- a/src/event/Event.php
+++ b/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;
diff --git a/src/event/HandlerList.php b/src/event/HandlerList.php
index 40d4fc566..7774ea840 100644
--- a/src/event/HandlerList.php
+++ b/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;
+	}
 }
diff --git a/src/event/RegisteredListenerCache.php b/src/event/RegisteredListenerCache.php
new file mode 100644
index 000000000..1b675c716
--- /dev/null
+++ b/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;
+}