Folia/patches/server/0025-Properly-cancel-chunk-load-tasks-that-were-not-sched.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Mon, 15 May 2023 12:24:17 -0700
Subject: [PATCH] Properly cancel chunk load tasks that were not scheduled

Since the chunk load task was not scheduled, the entity/poi load
task fields will not be set, but the task complete counter
will not be adjusted. Thus, the chunk load task will not complete.

To resolve this, detect when the entity/poi tasks were not scheduled
and decrement the task complete counter in such cases.

diff --git a/src/main/java/io/papermc/paper/chunk/system/scheduling/ChunkLoadTask.java b/src/main/java/io/papermc/paper/chunk/system/scheduling/ChunkLoadTask.java
index 7b8362625b48f1829ed4fd3c7fde6a4bec8e4099..be53c4b4a10463ef27f6fa178f17f92ca866e2e6 100644
--- a/src/main/java/io/papermc/paper/chunk/system/scheduling/ChunkLoadTask.java
+++ b/src/main/java/io/papermc/paper/chunk/system/scheduling/ChunkLoadTask.java
@@ -126,7 +126,9 @@ public final class ChunkLoadTask extends ChunkProgressionTask {
     public void cancel() {
         // must be before load task access, so we can synchronise with the writes to the fields
         final ca.spottedleaf.concurrentutil.lock.ReentrantAreaLock.Node schedulingLock = this.scheduler.schedulingLockArea.lock(this.chunkX, this.chunkZ); // Folia - use area based lock to reduce contention
+        final boolean scheduled; // Folia - fix cancellation of chunk load task
         try {
+            scheduled = this.scheduled; // Folia - fix cancellation of chunk load task - must read field here, as it may be written later conucrrently - we need to know if we scheduled _before_ cancellation
             this.cancelled = true;
         } finally {
             this.scheduler.schedulingLockArea.unlock(schedulingLock); // Folia - use area based lock to reduce contention
@@ -139,16 +141,29 @@ public final class ChunkLoadTask extends ChunkProgressionTask {
         the chunk load task attempts to complete with a non-null value
         */
 
-        if (this.entityLoadTask != null) {
-            if (this.entityLoadTask.cancel()) {
-                this.tryCompleteLoad();
+        // Folia start - fix cancellation of chunk load task
+        if (scheduled) {
+            // since we scheduled, we need to cancel the tasks
+            if (this.entityLoadTask != null) {
+                if (this.entityLoadTask.cancel()) {
+                    this.tryCompleteLoad();
+                }
             }
-        }
-        if (this.poiLoadTask != null) {
-            if (this.poiLoadTask.cancel()) {
-                this.tryCompleteLoad();
+            if (this.poiLoadTask != null) {
+                if (this.poiLoadTask.cancel()) {
+                    this.tryCompleteLoad();
+                }
             }
+        } else {
+            // since nothing was scheduled, we need to decrement the task count here ourselves
+
+            // for entity load task
+            this.tryCompleteLoad();
+
+            // for poi load task
+            this.tryCompleteLoad();
         }
+        // Folia end - fix cancellation of chunk load task
         this.loadTask.cancel();
     }