PaperMC/patches/server/0672-Synchronize-PalettedContainer-instead-of-ReentrantLo.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 ReentrantLock

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 wrote 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 cdd357a8dd82cfd2a8abd45c1b7937b409af4b05..5bbbb10a567963a451db8cf29d8d16f1cd013a16 100644
--- a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
+++ b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
@@ -35,17 +35,17 @@ public class PalettedContainer<T> implements PaletteResize<T> {
     private final ThreadingDetector threadingDetector = new ThreadingDetector("PalettedContainer");
 
     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
     @Deprecated public static <T> Codec<PalettedContainer<T>> codec(IdMap<T> idList, Codec<T> entryCodec, PalettedContainer.Strategy provider, T object) { return PalettedContainer.codec(idList, entryCodec, provider, object, null); } // Notice for updates: Please make sure this function isn't used anywhere
     public static <T> Codec<PalettedContainer<T>> codec(IdMap<T> idList, Codec<T> entryCodec, PalettedContainer.Strategy provider, T object, T[] presetValues) {
-        return RecordCodecBuilder.create((instance) -> {
+        return RecordCodecBuilder.<DiscData<T>>create((instance) -> { // Paper - decompile fixes
             return instance.group(entryCodec.mapResult(ExtraCodecs.orElsePartial(object)).listOf().fieldOf("palette").forGetter(PalettedContainer.DiscData::paletteEntries), Codec.LONG_STREAM.optionalFieldOf("data").forGetter(PalettedContainer.DiscData::storage)).apply(instance, PalettedContainer.DiscData::new);
         }).comapFlatMap((serialized) -> {
             return read(idList, provider, serialized, object, presetValues);
@@ -143,7 +143,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
     }
     // Paper end
 
-    public T getAndSet(int x, int y, int z, T value) {
+    public synchronized T getAndSet(int x, int y, int z, T value) { // Paper - synchronize
         this.acquire();
 
         Object var5;
@@ -166,7 +166,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
         return this.data.palette.valueFor(j);
     }
 
-    public void set(int x, int y, int z, T value) {
+    public synchronized void set(int x, int y, int z, T value) { // Paper - synchronize
         this.acquire();
 
         try {
@@ -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, com.destroystokyo.paper.antixray.ChunkPacketInfo<T> chunkPacketInfo, int bottomBlockY) {
+    public synchronized void write(FriendlyByteBuf buf, com.destroystokyo.paper.antixray.ChunkPacketInfo<T> chunkPacketInfo, int bottomBlockY) { // Paper - synchronize
         this.acquire();
 
         try {
@@ -236,7 +236,7 @@ public class PalettedContainer<T> implements PaletteResize<T> {
 
     }
 
-    private static <T> DataResult<PalettedContainer<T>> read(IdMap<T> idList, PalettedContainer.Strategy provider, PalettedContainer.DiscData<T> serialized, T defaultValue, T[] presetValues) { // Paper - Anti-Xray - Add preset values
+    private synchronized static <T> DataResult<PalettedContainer<T>> read(IdMap<T> idList, PalettedContainer.Strategy provider, PalettedContainer.DiscData<T> serialized, T defaultValue, T[] presetValues) { // Paper - Anti-Xray - Add preset values // Paper - synchronize
         List<T> list = serialized.paletteEntries();
         int i = provider.size();
         int j = provider.calculateBitsForSerialization(idList, list.size());
@@ -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;