SPIGOT-2255: Nether Structure generation ConcurrentModificationException

nms-patches/StructureGenerator.patch

@@ -0,0 +1,38 @@
+--- a/net/minecraft/server/StructureGenerator.java
++++ b/net/minecraft/server/StructureGenerator.java
+@@ -94,7 +94,7 @@
+         return this.c(blockposition) != null;
+     }
+ 
+-    protected StructureStart c(BlockPosition blockposition) {
++    protected synchronized StructureStart c(BlockPosition blockposition) { // CraftBukkit - synchronized
+         Iterator iterator = this.c.values().iterator();
+ 
+         while (iterator.hasNext()) {
+@@ -116,7 +116,7 @@
+         return null;
+     }
+ 
+-    public boolean b(World world, BlockPosition blockposition) {
++    public synchronized boolean b(World world, BlockPosition blockposition) { // CraftBukkit - synchronized
+         this.a(world);
+         Iterator iterator = this.c.values().iterator();
+ 
+@@ -133,7 +133,7 @@
+         return true;
+     }
+ 
+-    public BlockPosition getNearestGeneratedFeature(World world, BlockPosition blockposition) {
++    public synchronized BlockPosition getNearestGeneratedFeature(World world, BlockPosition blockposition) { // CraftBukkit - synchronized
+         this.g = world;
+         this.a(world);
+         this.f.setSeed(world.getSeed());
+@@ -195,7 +195,7 @@
+         return null;
+     }
+ 
+-    protected void a(World world) {
++    protected synchronized void a(World world) { // CraftBukkit - synchronized
+         if (this.a == null) {
+             this.a = (PersistentStructure) world.a(PersistentStructure.class, this.a());
+             if (this.a == null) {