Paper/patches/server/0756-Correctly-handle-recursion-for-chunkholder-updates.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sun, 21 Mar 2021 17:32:47 -0700
Subject: [PATCH] Correctly handle recursion for chunkholder updates

If a chunk ticket level is brought up while unloading it would
cause a recursive call which would handle the increase but then
the caller would think the chunk would be unloaded.

diff --git a/src/main/java/net/minecraft/server/level/ChunkHolder.java b/src/main/java/net/minecraft/server/level/ChunkHolder.java
index e844ac574e4b94580a14027c130374f1287f7324..844a0e1ac3a6480c8d7b49debaada2c698432405 100644
--- a/src/main/java/net/minecraft/server/level/ChunkHolder.java
+++ b/src/main/java/net/minecraft/server/level/ChunkHolder.java
@@ -624,8 +624,10 @@ public class ChunkHolder {
         playerchunkmap.onFullChunkStatusChange(this.pos, playerchunk_state);
     }
 
+    protected long updateCount; // Paper - correctly handle recursion
     protected void updateFutures(ChunkMap chunkStorage, Executor executor) {
         ensureTickThread("Async ticket level update"); // Paper
+        long updateCount = ++this.updateCount; // Paper - correctly handle recursion
         ChunkStatus chunkstatus = ChunkHolder.getStatus(this.oldTicketLevel);
         ChunkStatus chunkstatus1 = ChunkHolder.getStatus(this.ticketLevel);
         boolean flag = this.oldTicketLevel <= ChunkMap.MAX_CHUNK_DISTANCE;
@@ -667,6 +669,12 @@ public class ChunkHolder {
 
             // Run callback right away if the future was already done
             chunkStorage.callbackExecutor.run();
+            // Paper start - correctly handle recursion
+            if (this.updateCount != updateCount) {
+                // something else updated ticket level for us.
+                return;
+            }
+            // Paper end - correctly handle recursion
         }
         // CraftBukkit end
         CompletableFuture completablefuture;