MC-183249: Don't generate Carving Masks BitSet unless needed

This was using SIGNIFICANT amounts of memory allocating many
long[]'s for BitSets for every ProtoChunk in the cache that had
been unloaded and reloaded.

This will result in a nice memory reduction.

Spigot-Server-Patches/0510-MC-183249-Don-t-generate-Carving-Masks-BitSet-unless.patch

@@ -0,0 +1,43 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Sat, 9 May 2020 12:11:47 -0400
+Subject: [PATCH] MC-183249: Don't generate Carving Masks BitSet unless needed
+
+This was using SIGNIFICANT amounts of memory allocating many
+long[]'s for BitSets for every ProtoChunk in the cache that had
+been unloaded and reloaded.
+
+This will result in a nice memory reduction.
+
+diff --git a/src/main/java/net/minecraft/server/ChunkRegionLoader.java b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+index fa893b14bcef9bab6891dea2c4375b09d74ac038..e625842e524f18e469f7695b27d52d4d04892266 100644
+--- a/src/main/java/net/minecraft/server/ChunkRegionLoader.java
++++ b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+@@ -472,7 +472,12 @@ public class ChunkRegionLoader {
+             for (int l = 0; l < k; ++l) {
+                 WorldGenStage.Features worldgenstage_features = aworldgenstage_features[l];
+ 
+-                nbttagcompound3.setByteArray(worldgenstage_features.toString(), ichunkaccess.a(worldgenstage_features).toByteArray());
++                // Paper start - don't create carving mask bitsets if not even at that chunk status yet
++                BitSet mask = protochunk.getCarvingMaskIfSet(worldgenstage_features);
++                if (mask != null) {
++                    nbttagcompound3.setByteArray(worldgenstage_features.toString(), mask.toByteArray());
++                }
++                // Paper end
+             }
+ 
+             nbttagcompound1.set("CarvingMasks", nbttagcompound3);
+diff --git a/src/main/java/net/minecraft/server/ProtoChunk.java b/src/main/java/net/minecraft/server/ProtoChunk.java
+index deb7fb090196c4a33c0bb224f1c4e899aa3cd8c3..9223ef9545be4a87b421e25ebe3f5b7ad72c4726 100644
+--- a/src/main/java/net/minecraft/server/ProtoChunk.java
++++ b/src/main/java/net/minecraft/server/ProtoChunk.java
+@@ -43,7 +43,8 @@ public class ProtoChunk implements IChunkAccess {
+     private final ProtoChunkTickList<Block> q;
+     private final ProtoChunkTickList<FluidType> r;
+     private long s;
+-    private final Map<WorldGenStage.Features, BitSet> t;
++    private final Map<WorldGenStage.Features, BitSet> t;public BitSet getCarvingMaskIfSet(WorldGenStage.Features worldgenstage_features) { return this.t.get(worldgenstage_features); } // Paper
++    // Paper end
+     private volatile boolean u;
+     private final World world; // Paper - Anti-Xray - Add world
+