PaperMC/patches/server/0739-Fix-chunks-refusing-to-unload-at-low-TPS.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Mon, 1 Feb 2021 15:35:14 -0800
Subject: [PATCH] Fix chunks refusing to unload at low TPS

The full chunk future is appended to the chunk save future, but
when moving to unloaded ticket level it is not being completed with
the empty chunk access, so the chunk save must wait for the full
chunk future to complete. We can simply schedule to the immediate
executor to get this effect, rather than the main mailbox.

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 2af478902b528f335797c691730afb2657d4e6c4..71ca2c2edc6a89e9365b4686c233f60cea12a472 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -1259,9 +1259,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
                 return chunk;
             });
-        }, (runnable) -> {
-            this.mainThreadMailbox.tell(ChunkTaskPriorityQueueSorter.message(playerchunk, runnable));
-        });
+        }, this.mainThreadExecutor); // Paper - queue to execute immediately so this doesn't delay chunk unloading
     }
 
     public int getTickingGenerated() {