PaperMC/patches/server/0662-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 45a969f97b26e328e34f3d576557999c32b954a2..277b75940d0424051919889b2d0045f313027234 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> {
     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 - Anti-Xray - Add preset values
@@ -113,7 +113,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
     }
 
     @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
@@ -160,7 +160,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
         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);
@@ -177,7 +177,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
 
     }
 
-    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);
     }
@@ -200,7 +200,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
         });
     }
 
-    public void read(FriendlyByteBuf buf) {
+    public synchronized void read(FriendlyByteBuf buf) { // Paper - synchronize
         this.acquire();
 
         try {
@@ -218,7 +218,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
 
     // Paper start - Anti-Xray - Add chunk packet info
     @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 {
@@ -275,7 +275,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
         return DataResult.success(new PalettedContainer<>(idList, provider, configuration, bitStorage, list, defaultValue, presetValues)); // Paper - Anti-Xray - Add preset values
     }
 
-    private PalettedContainer.DiscData<T> write(IdMap<T> idList, PalettedContainer.Strategy provider) {
+    private synchronized PalettedContainer.DiscData<T> write(IdMap<T> idList, PalettedContainer.Strategy provider) { // Paper - synchronize
         this.acquire();
 
         PalettedContainer.DiscData var12;