From b0456f32941d38b616e2e3f3f37583cb7a5713ef Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Sat, 25 Nov 2017 17:02:33 +0000
Subject: [PATCH] Do not use a snapshot for hoppers

In 1.12, Spigot improved their blockstate implementation to take a full
copy of the TE, this allows for a much better snapshot in that it will
actually retain all of the TE's state, it is a much more expensive
implementation. This is also implicated with their backwards compat
for inventories meaning that accessing of a snapshots inventory of a
placed block will actually access the inventory of the live TE, making
creation of a snapshot redundant if the only intent is to interact with
the TEs inventory.

Hoppers are a horrible hit, every attempt to transfer an ItemStack will
result in two TileEntity state snapshots, with two hoppers and a double chest
ontop, I managed to log 380 cases per second where a snapshot would have been
taken in cases where the snapshot is redundant.

diff --git a/src/main/java/net/minecraft/server/TileEntityHopper.java b/src/main/java/net/minecraft/server/TileEntityHopper.java
index 8ad081316..ebbe5d326 100644
--- a/src/main/java/net/minecraft/server/TileEntityHopper.java
+++ b/src/main/java/net/minecraft/server/TileEntityHopper.java
@@ -219,11 +219,15 @@ public class TileEntityHopper extends TileEntityLootable implements IHopper, ITi
                         // Have to special case large chests as they work oddly
                         if (iinventory instanceof InventoryLargeChest) {
                             destinationInventory = new org.bukkit.craftbukkit.inventory.CraftInventoryDoubleChest((InventoryLargeChest) iinventory);
+                        // Paper start - avoid redundant snapshot creation of a TE
+                        } else if (iinventory instanceof TileEntity) {
+                            destinationInventory = ((TileEntity) iinventory).getOwner(false).getInventory();
                         } else {
                             destinationInventory = iinventory.getOwner().getInventory();
                         }
 
-                        InventoryMoveItemEvent event = new InventoryMoveItemEvent(this.getOwner().getInventory(), oitemstack.clone(), destinationInventory, true);
+                        InventoryMoveItemEvent event = new InventoryMoveItemEvent(this.getOwner(false).getInventory(), oitemstack.clone(), destinationInventory, true);
+                        // Paper end - avoid redundant snapshot creation of a TE
                         this.getWorld().getServer().getPluginManager().callEvent(event);
                         if (event.isCancelled()) {
                             this.setItem(i, itemstack);
@@ -379,12 +383,22 @@ public class TileEntityHopper extends TileEntityLootable implements IHopper, ITi
             // Have to special case large chests as they work oddly
             if (iinventory instanceof InventoryLargeChest) {
                 sourceInventory = new org.bukkit.craftbukkit.inventory.CraftInventoryDoubleChest((InventoryLargeChest) iinventory);
+            // Paper start - avoid redundant snapshot creation of a TE
+            } else if (iinventory instanceof TileEntity){
+                sourceInventory = ((TileEntity) iinventory).getOwner(false).getInventory();
             } else {
                 sourceInventory = iinventory.getOwner().getInventory();
             }
 
-            InventoryMoveItemEvent event = new InventoryMoveItemEvent(sourceInventory, oitemstack.clone(), ihopper.getOwner().getInventory(), false);
+            Inventory destination;
+            if (ihopper instanceof TileEntity) {
+                destination = ((TileEntity) ihopper).getOwner(false).getInventory();
+            } else {
+                destination = ihopper.getOwner().getInventory();
+            }
 
+            InventoryMoveItemEvent event = new InventoryMoveItemEvent(sourceInventory, oitemstack.clone(), destination, false);
+            // Paper end - avoid redundant snapshot creation of a TE
             ihopper.getWorld().getServer().getPluginManager().callEvent(event);
             if (event.isCancelled()) {
                 iinventory.setItem(i, itemstack1);
-- 
2.15.0