PaperMC/patches/server/0658-Synchronize-PalettedContainer-instead-of-ThreadingDe.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 29 May 2020 20:29:02 -0400
Subject: [PATCH] Synchronize PalettedContainer instead of
 ThreadingDetector/Semaphore

Mojang has flaws in their logic about chunks being concurrently
wrote to. So we constantly see crashes around multiple threads writing.

Additionally, java has optimized synchronization so well that its
in many times faster than trying to manage read write locks for low
contention situations.

And this is extremely a low contention situation.

diff --git a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
index 0a174b07e58f638e75a013552c964a9fb833d4cb..6800452604e0db660e8d5dca9778abd6e2f66478 100644
--- a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
+++ b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
@@ -32,14 +32,14 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
     private final T @org.jetbrains.annotations.Nullable [] presetValues; // Paper - Anti-Xray - Add preset values
     private volatile PalettedContainer.Data<T> data;
     private final PalettedContainer.Strategy strategy;
-    private final ThreadingDetector threadingDetector = new ThreadingDetector("PalettedContainer");
+    // private final ThreadingDetector threadingDetector = new ThreadingDetector("PalettedContainer"); // Paper - unused
 
     public void acquire() {
-        this.threadingDetector.checkAndLock();
+        // this.threadingDetector.checkAndLock(); // Paper - disable this - use proper synchronization
     }
 
     public void release() {
-        this.threadingDetector.checkAndUnlock();
+        // this.threadingDetector.checkAndUnlock(); // Paper - disable this
     }
 
     // Paper start
@@ -130,7 +130,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
     }
 
     @Override
-    public int onResize(int newBits, T object) {
+    public synchronized int onResize(int newBits, T object) { // Paper - synchronize
         PalettedContainer.Data<T> data = this.data;
 
         // Paper start - Anti-Xray - Add preset values
@@ -177,7 +177,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
         return this.getAndSet(this.strategy.getIndex(x, y, z), value);
     }
 
-    private T getAndSet(int index, T value) {
+    private synchronized T getAndSet(int index, T value) { // Paper - synchronize
         int i = this.data.palette.idFor(value);
         int j = this.data.storage.getAndSet(index, i);
         return this.data.palette.valueFor(j);
@@ -194,7 +194,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
 
     }
 
-    private void set(int index, T value) {
+    private synchronized void set(int index, T value) { // Paper - synchronize
         int i = this.data.palette.idFor(value);
         this.data.storage.set(index, i);
     }
@@ -219,7 +219,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
         });
     }
 
-    public void read(FriendlyByteBuf buf) {
+    public synchronized void read(FriendlyByteBuf buf) { // Paper - synchronize
         this.acquire();
 
         try {
@@ -237,7 +237,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
 
     // Paper start - Anti-Xray - Add chunk packet info
     @Override @Deprecated public void write(FriendlyByteBuf buf) { this.write(buf, null, 0); } // Notice for updates: Please make sure this method isn't used anywhere
-    public void write(FriendlyByteBuf buf, @Nullable com.destroystokyo.paper.antixray.ChunkPacketInfo<T> chunkPacketInfo, int bottomBlockY) {
+    public synchronized void write(FriendlyByteBuf buf, @Nullable com.destroystokyo.paper.antixray.ChunkPacketInfo<T> chunkPacketInfo, int bottomBlockY) { // Paper - synchronize
         this.acquire();
 
         try {
@@ -295,7 +295,7 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
     }
 
     @Override
-    public PalettedContainerRO.PackedData<T> pack(IdMap<T> idMap, PalettedContainer.Strategy strategy) {
+    public synchronized PalettedContainerRO.PackedData<T> pack(IdMap<T> idMap, PalettedContainer.Strategy strategy) { // Paper - synchronize
         this.acquire();
 
         PalettedContainerRO.PackedData var12;