spigot/CraftBukkit-Patches/0084-Remove-DataWatcher-Locking.patch

From 56e2a413b4e3fee227e9730c3fafc921039f0a6d Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Tue, 9 Jul 2019 02:18:54 -0700
Subject: [PATCH] Remove DataWatcher Locking

The lock in DataWatcher is used to prevent concurrent modifications,
however any modifications to this map only occur on initialization of
an Entity in its constructor.

Every other access is through a readlock, which allows the threads to
pass if there is no thread holding the writelock.

Since the writelock is only obtained in the constructor of the Entity,
the further readlocks are actually useless.

This patch also changes the entries map to be fastutil
int2objectopenhashmap for performance.

diff --git a/src/main/java/net/minecraft/network/syncher/DataWatcher.java b/src/main/java/net/minecraft/network/syncher/DataWatcher.java
index ac10ddf352..78d4756490 100644
--- a/src/main/java/net/minecraft/network/syncher/DataWatcher.java
+++ b/src/main/java/net/minecraft/network/syncher/DataWatcher.java
@@ -36,7 +36,7 @@ public class DataWatcher {
     private static final int MAX_ID_VALUE = 254;
     private final Entity entity;
     private final Int2ObjectMap<DataWatcher.Item<?>> itemsById = new Int2ObjectOpenHashMap();
-    private final ReadWriteLock lock = new ReentrantReadWriteLock();
+    // private final ReadWriteLock lock = new ReentrantReadWriteLock(); // Spigot - not required
     private boolean isDirty;
 
     public DataWatcher(Entity entity) {
@@ -83,7 +83,9 @@ public class DataWatcher {
         }
     }
 
+    public boolean registrationLocked; // Spigot
     public <T> void define(DataWatcherObject<T> datawatcherobject, T t0) {
+        if (this.registrationLocked) throw new IllegalStateException("Registering datawatcher object after entity initialization"); // Spigot
         int i = datawatcherobject.getId();
 
         if (i > 254) {
@@ -102,9 +104,9 @@ public class DataWatcher {
     private <T> void createDataItem(DataWatcherObject<T> datawatcherobject, T t0) {
         DataWatcher.Item<T> datawatcher_item = new DataWatcher.Item<>(datawatcherobject, t0);
 
-        this.lock.writeLock().lock();
+        // this.lock.writeLock().lock(); // Spigot - not required
         this.itemsById.put(datawatcherobject.getId(), datawatcher_item);
-        this.lock.writeLock().unlock();
+        // this.lock.writeLock().unlock(); // Spigot - not required
     }
 
     public <T> boolean hasItem(DataWatcherObject<T> datawatcherobject) {
@@ -112,6 +114,8 @@ public class DataWatcher {
     }
 
     private <T> DataWatcher.Item<T> getItem(DataWatcherObject<T> datawatcherobject) {
+        // Spigot start
+        /*
         this.lock.readLock().lock();
 
         DataWatcher.Item datawatcher_item;
@@ -129,6 +133,9 @@ public class DataWatcher {
         }
 
         return datawatcher_item;
+        */
+        return (DataWatcher.Item) this.itemsById.get(datawatcherobject.getId());
+        // Spigot end
     }
 
     public <T> T get(DataWatcherObject<T> datawatcherobject) {
@@ -167,7 +174,7 @@ public class DataWatcher {
         List<DataWatcher.b<?>> list = null;
 
         if (this.isDirty) {
-            this.lock.readLock().lock();
+            // this.lock.readLock().lock(); // Spigot - not required
             ObjectIterator objectiterator = this.itemsById.values().iterator();
 
             while (objectiterator.hasNext()) {
@@ -183,7 +190,7 @@ public class DataWatcher {
                 }
             }
 
-            this.lock.readLock().unlock();
+            // this.lock.readLock().unlock(); // Spigot - not required
         }
 
         this.isDirty = false;
@@ -194,7 +201,7 @@ public class DataWatcher {
     public List<DataWatcher.b<?>> getNonDefaultValues() {
         List<DataWatcher.b<?>> list = null;
 
-        this.lock.readLock().lock();
+        // this.lock.readLock().lock(); // Spigot - not required
         ObjectIterator objectiterator = this.itemsById.values().iterator();
 
         while (objectiterator.hasNext()) {
@@ -209,12 +216,12 @@ public class DataWatcher {
             }
         }
 
-        this.lock.readLock().unlock();
+        // this.lock.readLock().unlock(); // Spigot - not required
         return list;
     }
 
     public void assignValues(List<DataWatcher.b<?>> list) {
-        this.lock.writeLock().lock();
+        // this.lock.writeLock().lock(); // Spigot - not required
 
         try {
             Iterator iterator = list.iterator();
@@ -229,7 +236,7 @@ public class DataWatcher {
                 }
             }
         } finally {
-            this.lock.writeLock().unlock();
+            // this.lock.writeLock().unlock(); // Spigot - not required
         }
 
         this.entity.onSyncedDataUpdated(list);
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index 3f6e973f3b..5e15c69863 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -375,6 +375,7 @@ public abstract class Entity implements INamableTileEntity, EntityAccess, IComma
         this.entityData.define(Entity.DATA_POSE, EntityPose.STANDING);
         this.entityData.define(Entity.DATA_TICKS_FROZEN, 0);
         this.defineSynchedData();
+        this.getEntityData().registrationLocked = true; // Spigot
         this.setPos(0.0D, 0.0D, 0.0D);
         this.eyeHeight = this.getEyeHeight(EntityPose.STANDING, this.dimensions);
     }
-- 
2.43.0