From c4f8064fb972fac5030eccda3f6bc55591d39749 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.
---
 .../level/chunk/PalettedContainer.java.patch  | 74 +++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 paper-server/patches/sources/net/minecraft/world/level/chunk/PalettedContainer.java.patch

diff --git a/paper-server/patches/sources/net/minecraft/world/level/chunk/PalettedContainer.java.patch b/paper-server/patches/sources/net/minecraft/world/level/chunk/PalettedContainer.java.patch
new file mode 100644
index 0000000000..aff5b81eae
--- /dev/null
+++ b/paper-server/patches/sources/net/minecraft/world/level/chunk/PalettedContainer.java.patch
@@ -0,0 +1,74 @@
+--- a/net/minecraft/world/level/chunk/PalettedContainer.java
++++ b/net/minecraft/world/level/chunk/PalettedContainer.java
+@@ -30,14 +30,14 @@
+     public final IdMap<T> registry;
+     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
+     }
+ 
+     public static <T> Codec<PalettedContainer<T>> codecRW(IdMap<T> idList, Codec<T> entryCodec, PalettedContainer.Strategy paletteProvider, T defaultValue) {
+@@ -110,7 +110,7 @@
+     }
+ 
+     @Override
+-    public int onResize(int newBits, T object) {
++    public synchronized int onResize(int newBits, T object) { // Paper - synchronize
+         PalettedContainer.Data<T> data = this.data;
+         PalettedContainer.Data<T> data2 = this.createOrReuseData(data, newBits);
+         data2.copyFrom(data.palette, data.storage);
+@@ -135,7 +135,7 @@
+         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);
+@@ -151,7 +151,7 @@
+         }
+     }
+ 
+-    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);
+     }
+@@ -174,7 +174,7 @@
+         intSet.forEach(id -> action.accept(palette.valueFor(id)));
+     }
+ 
+-    public void read(FriendlyByteBuf buf) {
++    public synchronized void read(FriendlyByteBuf buf) { // Paper - synchronize
+         this.acquire();
+ 
+         try {
+@@ -189,7 +189,7 @@
+     }
+ 
+     @Override
+-    public void write(FriendlyByteBuf buf) {
++    public synchronized void write(FriendlyByteBuf buf) { // Paper - synchronize
+         this.acquire();
+ 
+         try {
+@@ -237,7 +237,7 @@
+     }
+ 
+     @Override
+-    public PalettedContainerRO.PackedData<T> pack(IdMap<T> idList, PalettedContainer.Strategy paletteProvider) {
++    public synchronized PalettedContainerRO.PackedData<T> pack(IdMap<T> idList, PalettedContainer.Strategy paletteProvider) { // Paper - synchronize
+         this.acquire();
+ 
+         PalettedContainerRO.PackedData var12;