From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: MrPowerGamerBR <git@mrpowergamerbr.com>
Date: Sun, 19 Nov 2023 12:35:16 -0300
Subject: [PATCH] Skip EntityScheduler's executeTick checks if there isn't any
 tasks to be run

On each tick, Paper runs EntityScheduler's executeTick of each entity. This is a bit expensive, due to ArrayDeque's size() call because it ain't a simple "get the current queue size" function, and due to the thread checks.

To avoid the hefty ArrayDeque's size() call, we check if we *really* need to execute the executeTick, by checking if currentlyExecuting is not empty or if oneTimeDelayed is not empty.

Most entities won't have any scheduled tasks, so this is a nice performance bonus. These optimizations, however, wouldn't work in a Folia environment, but because in SparklyPaper executeTick is always executed on the main thread, it ain't an issue for us (yay).

diff --git a/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java b/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java
index 62484ebf4550b05182f693a3180bbac5d5fd906d..9e15a2a9e47a5b50c3c9e2afce2eb0f48ed0fdaf 100644
--- a/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java
+++ b/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java
@@ -45,6 +45,7 @@ public final class EntityScheduler {
     private final Long2ObjectOpenHashMap<List<ScheduledTask>> oneTimeDelayed = new Long2ObjectOpenHashMap<>();
 
     private final ArrayDeque<ScheduledTask> currentlyExecuting = new ArrayDeque<>();
+    private boolean hasScheduledAtLeastOneTask = false; // SparklyPaper - skip EntityScheduler's executeTick checks if there isn't any tasks to be run
 
     public EntityScheduler(final CraftEntity entity) {
         this.entity = Validate.notNull(entity);
@@ -124,6 +125,7 @@ public final class EntityScheduler {
             if (this.tickCount == RETIRED_TICK_COUNT) {
                 return false;
             }
+            hasScheduledAtLeastOneTask = true; // SparklyPaper - skip EntityScheduler's executeTick checks if there isn't any tasks to be run
             this.oneTimeDelayed.computeIfAbsent(this.tickCount + Math.max(1L, delay), (final long keyInMap) -> {
                 return new ArrayList<>();
             }).add(task);
@@ -138,15 +140,34 @@ public final class EntityScheduler {
      * @throws IllegalStateException If the scheduler is retired.
      */
     public void executeTick() {
+        // SparklyPaper start - skip EntityScheduler's executeTick checks if there isn't any tasks to be run
+        // This wouldn't work on a multithreaded environment like Folia!!! But because the executeTick is always executed on the
+        // main thread, we don't need to care about concurrency
+        // First, we use a simple boolean check here
+        // Yeah, this sounds dumb but, after benchmarking, it seems like a simple boolean check like this is actually more performant than calling both is empty checks
+        // So first we check if the EntityScheduler has been used at least ONCE
+        // If it wasn't, then we skip all checks entirely
+        // We don't even need to update the tick count because the tick count is actually relative to this scheduler, not bound to the global current tick, so it isn't a big deal if we don't update the tick count
+        if (!this.hasScheduledAtLeastOneTask)
+            return;
+        if (this.tickCount == RETIRED_TICK_COUNT) {
+            throw new IllegalStateException("Ticking retired scheduler");
+        }
+        ++this.tickCount;
+        if (this.currentlyExecuting.isEmpty() && this.oneTimeDelayed.isEmpty()) // Check if we have any pending tasks and, if not, skip!
+            return;
+        // SparklyPaper end
         final Entity thisEntity = this.entity.getHandleRaw();
 
         TickThread.ensureTickThread(thisEntity, "May not tick entity scheduler asynchronously");
         final List<ScheduledTask> toRun;
         synchronized (this.stateLock) {
-            if (this.tickCount == RETIRED_TICK_COUNT) {
-                throw new IllegalStateException("Ticking retired scheduler");
-            }
-            ++this.tickCount;
+            // SparklyPaper start - skip EntityScheduler's executeTick checks if there isn't any tasks to be run
+            // if (this.tickCount == RETIRED_TICK_COUNT) {
+            //     throw new IllegalStateException("Ticking retired scheduler");
+            // }
+            // ++this.tickCount;
+            // SparklyPaper end
             if (this.oneTimeDelayed.isEmpty()) {
                 toRun = null;
             } else {