From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Wed, 8 Apr 2020 03:06:30 -0400
Subject: [PATCH] Optimize PlayerChunkMap memory use for visibleChunks

No longer clones visible chunks which is causing massive memory
allocation issues, likely the source of Humongous Objects on large servers.

Instead we just synchronize, clear and rebuild, reusing the same object buffers
as before with only 2 small objects created (FastIterator/MapEntry)

This should result in siginificant memory use reduction and improved GC behavior.

diff --git a/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java b/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java
new file mode 100644
index 0000000000000000000000000000000000000000..f6ff4d8132a95895680f5bc81f8f873e78f0bbdb
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java
@@ -0,0 +1,39 @@
+package com.destroystokyo.paper.util.map;
+
+import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
+
+public class Long2ObjectLinkedOpenHashMapFastCopy<V> extends Long2ObjectLinkedOpenHashMap<V> {
+
+    public void copyFrom(Long2ObjectLinkedOpenHashMapFastCopy<V> map) {
+        if (key.length != map.key.length) {
+            key = null;
+            key = new long[map.key.length];
+        }
+        if (value.length != map.value.length) {
+            value = null;
+            //noinspection unchecked
+            value = (V[]) new Object[map.value.length];
+        }
+        if (link.length != map.link.length) {
+            link = null;
+            link = new long[map.link.length];
+        }
+        System.arraycopy(map.key, 0, this.key, 0, map.key.length);
+        System.arraycopy(map.value, 0, this.value, 0, map.value.length);
+        System.arraycopy(map.link, 0, this.link, 0, map.link.length);
+        this.size = map.size;
+        this.mask = map.mask;
+        this.first = map.first;
+        this.last = map.last;
+        this.n = map.n;
+        this.maxFill = map.maxFill;
+        this.containsNullKey = map.containsNullKey;
+    }
+
+    @Override
+    public Long2ObjectLinkedOpenHashMapFastCopy<V> clone() {
+        Long2ObjectLinkedOpenHashMapFastCopy<V> clone = (Long2ObjectLinkedOpenHashMapFastCopy<V>) super.clone();
+        clone.copyFrom(this);
+        return clone;
+    }
+}
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index ce671ecabc402053b160df0f9d64d22b784d165c..dea7ff47f7a2934708d887c2c40f9328b78fc84e 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -757,7 +757,7 @@ public class ChunkProviderServer extends IChunkProvider {
                 entityPlayer.playerNaturallySpawnedEvent.callEvent();
             };
             // Paper end
-            this.playerChunkMap.f().forEach((playerchunk) -> { // Paper - no... just no...
+            this.playerChunkMap.forEachVisibleChunk((playerchunk) -> { // Paper - safe iterator incase chunk loads, also no wrapping
                 Optional<Chunk> optional = ((Either) playerchunk.a().getNow(PlayerChunk.UNLOADED_CHUNK)).left();
 
                 if (optional.isPresent()) {
diff --git a/src/main/java/net/minecraft/server/MCUtil.java b/src/main/java/net/minecraft/server/MCUtil.java
index c470c6527b214026c230feaae0c0875c86dea673..df3150072fd36dac28d83309e50342c9cfa326b3 100644
--- a/src/main/java/net/minecraft/server/MCUtil.java
+++ b/src/main/java/net/minecraft/server/MCUtil.java
@@ -599,7 +599,7 @@ public final class MCUtil {
 
             WorldServer world = ((org.bukkit.craftbukkit.CraftWorld)bukkitWorld).getHandle();
             PlayerChunkMap chunkMap = world.getChunkProvider().playerChunkMap;
-            Long2ObjectLinkedOpenHashMap<PlayerChunk> visibleChunks = chunkMap.visibleChunks;
+            Long2ObjectLinkedOpenHashMap<PlayerChunk> visibleChunks = chunkMap.getVisibleChunks();
             ChunkMapDistance chunkMapDistance = chunkMap.chunkDistanceManager;
             List<PlayerChunk> allChunks = new ArrayList<>(visibleChunks.values());
             List<EntityPlayer> players = world.players;
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index f839091ae4385e763a19d680585a9363fad6b744..d3a597d878de4cb625484cbf3a9838961d38ada0 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -57,8 +57,33 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 
     private static final Logger LOGGER = LogManager.getLogger();
     public static final int GOLDEN_TICKET = 33 + ChunkStatus.b();
-    public final Long2ObjectLinkedOpenHashMap<PlayerChunk> updatingChunks = new Long2ObjectLinkedOpenHashMap();
-    public volatile Long2ObjectLinkedOpenHashMap<PlayerChunk> visibleChunks;
+    // Paper start - faster copying
+    public final Long2ObjectLinkedOpenHashMap<PlayerChunk> updatingChunks = new com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<>(); // Paper - faster copying
+    public final Long2ObjectLinkedOpenHashMap<PlayerChunk> visibleChunks = new ProtectedVisibleChunksMap(); // Paper - faster copying
+
+    private class ProtectedVisibleChunksMap extends com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk> {
+        @Override
+        public PlayerChunk put(long k, PlayerChunk playerChunk) {
+            throw new UnsupportedOperationException("Updating visible Chunks");
+        }
+
+        @Override
+        public PlayerChunk remove(long k) {
+            throw new UnsupportedOperationException("Removing visible Chunks");
+        }
+
+        @Override
+        public PlayerChunk get(long k) {
+            return PlayerChunkMap.this.getVisibleChunk(k);
+        }
+
+        public PlayerChunk safeGet(long k) {
+            return super.get(k);
+        }
+    }
+    // Paper end
+    public final com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk> pendingVisibleChunks = new com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk>(); // Paper - this is used if the visible chunks is updated while iterating only
+    public transient com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk> visibleChunksClone; // Paper - used for async access of visible chunks, clone and cache only when needed
     private final Long2ObjectLinkedOpenHashMap<PlayerChunk> pendingUnload;
     final LongSet loadedChunks; // Paper - private -> package
     public final WorldServer world;
@@ -131,7 +156,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 
     public PlayerChunkMap(WorldServer worldserver, Convertable.ConversionSession convertable_conversionsession, DataFixer datafixer, DefinedStructureManager definedstructuremanager, Executor executor, IAsyncTaskHandler<Runnable> iasynctaskhandler, ILightAccess ilightaccess, ChunkGenerator chunkgenerator, WorldLoadListener worldloadlistener, Supplier<WorldPersistentData> supplier, int i, boolean flag) {
         super(new File(convertable_conversionsession.a(worldserver.getDimensionKey()), "region"), datafixer, flag);
-        this.visibleChunks = this.updatingChunks.clone();
+        //this.visibleChunks = this.updatingChunks.clone(); // Paper - no more cloning
         this.pendingUnload = new Long2ObjectLinkedOpenHashMap();
         this.loadedChunks = new LongOpenHashSet();
         this.unloadQueue = new LongOpenHashSet();
@@ -223,9 +248,52 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
         return (PlayerChunk) this.updatingChunks.get(i);
     }
 
+    // Paper start - remove cloning of visible chunks unless accessed as a collection async
+    private static final boolean DEBUG_ASYNC_VISIBLE_CHUNKS = Boolean.getBoolean("paper.debug-async-visible-chunks");
+    private boolean isIterating = false;
+    private boolean hasPendingVisibleUpdate = false;
+    public void forEachVisibleChunk(java.util.function.Consumer<PlayerChunk> consumer) {
+        org.spigotmc.AsyncCatcher.catchOp("forEachVisibleChunk");
+        boolean prev = isIterating;
+        isIterating = true;
+        try {
+            for (PlayerChunk value : this.visibleChunks.values()) {
+                consumer.accept(value);
+            }
+        } finally {
+            this.isIterating = prev;
+            if (!this.isIterating && this.hasPendingVisibleUpdate) {
+                ((ProtectedVisibleChunksMap)this.visibleChunks).copyFrom(this.pendingVisibleChunks);
+                this.pendingVisibleChunks.clear();
+                this.hasPendingVisibleUpdate = false;
+            }
+        }
+    }
+    public Long2ObjectLinkedOpenHashMap<PlayerChunk> getVisibleChunks() {
+        if (Thread.currentThread() == this.world.serverThread) {
+            return this.visibleChunks;
+        } else {
+            synchronized (this.visibleChunks) {
+                if (DEBUG_ASYNC_VISIBLE_CHUNKS) new Throwable("Async getVisibleChunks").printStackTrace();
+                if (this.visibleChunksClone == null) {
+                    this.visibleChunksClone = this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.clone() : ((ProtectedVisibleChunksMap)this.visibleChunks).clone();
+                }
+                return this.visibleChunksClone;
+            }
+        }
+    }
+    // Paper end
+
     @Nullable
     public PlayerChunk getVisibleChunk(long i) { // Paper - protected -> public
-        return (PlayerChunk) this.visibleChunks.get(i);
+        // Paper start - mt safe get
+        if (Thread.currentThread() != this.world.serverThread) {
+            synchronized (this.visibleChunks) {
+                return (PlayerChunk) (this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.get(i) : ((ProtectedVisibleChunksMap)this.visibleChunks).safeGet(i));
+            }
+        }
+        return (PlayerChunk) (this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.get(i) : ((ProtectedVisibleChunksMap)this.visibleChunks).safeGet(i));
+        // Paper end
     }
 
     protected IntSupplier c(long i) {
@@ -413,8 +481,9 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     // Paper end
 
     protected void save(boolean flag) {
+        Long2ObjectLinkedOpenHashMap<PlayerChunk> visibleChunks = this.getVisibleChunks(); // Paper remove clone of visible Chunks unless saving off main thread (watchdog kill)
         if (flag) {
-            List<PlayerChunk> list = (List) this.visibleChunks.values().stream().filter(PlayerChunk::hasBeenLoaded).peek(PlayerChunk::m).collect(Collectors.toList());
+            List<PlayerChunk> list = (List) visibleChunks.values().stream().filter(PlayerChunk::hasBeenLoaded).peek(PlayerChunk::m).collect(Collectors.toList()); // Paper - remove cloning of visible chunks
             MutableBoolean mutableboolean = new MutableBoolean();
 
             do {
@@ -442,7 +511,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 //            this.i(); // Paper - nuke IOWorker
             PlayerChunkMap.LOGGER.info("ThreadedAnvilChunkStorage ({}): All chunks are saved", this.w.getName());
         } else {
-            this.visibleChunks.values().stream().filter(PlayerChunk::hasBeenLoaded).forEach((playerchunk) -> {
+            visibleChunks.values().stream().filter(PlayerChunk::hasBeenLoaded).forEach((playerchunk) -> {
                 IChunkAccess ichunkaccess = (IChunkAccess) playerchunk.getChunkSave().getNow(null); // CraftBukkit - decompile error
 
                 if (ichunkaccess instanceof ProtoChunkExtension || ichunkaccess instanceof Chunk) {
@@ -613,7 +682,20 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
         if (!this.updatingChunksModified) {
             return false;
         } else {
-            this.visibleChunks = this.updatingChunks.clone();
+            // Paper start - stop cloning visibleChunks
+            synchronized (this.visibleChunks) {
+                if (isIterating) {
+                    hasPendingVisibleUpdate = true;
+                    this.pendingVisibleChunks.copyFrom((com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk>)this.updatingChunks);
+                } else {
+                    hasPendingVisibleUpdate = false;
+                    this.pendingVisibleChunks.clear();
+                    ((ProtectedVisibleChunksMap)this.visibleChunks).copyFrom((com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<PlayerChunk>)this.updatingChunks);
+                    this.visibleChunksClone = null;
+                }
+            }
+            // Paper end
+
             this.updatingChunksModified = false;
             return true;
         }
@@ -1084,12 +1166,12 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     }
 
     protected Iterable<PlayerChunk> f() {
-        return Iterables.unmodifiableIterable(this.visibleChunks.values());
+        return Iterables.unmodifiableIterable(this.getVisibleChunks().values()); // Paper
     }
 
     void a(Writer writer) throws IOException {
         CSVWriter csvwriter = CSVWriter.a().a("x").a("z").a("level").a("in_memory").a("status").a("full_status").a("accessible_ready").a("ticking_ready").a("entity_ticking_ready").a("ticket").a("spawning").a("entity_count").a("block_entity_count").a(writer);
-        ObjectBidirectionalIterator objectbidirectionaliterator = this.visibleChunks.long2ObjectEntrySet().iterator();
+        ObjectBidirectionalIterator objectbidirectionaliterator = this.getVisibleChunks().long2ObjectEntrySet().iterator(); // Paper
 
         while (objectbidirectionaliterator.hasNext()) {
             Entry<PlayerChunk> entry = (Entry) objectbidirectionaliterator.next();
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 20aeec95138a08accc4cb7b1f2d80d63bb9bf920..5ef12e85d7374c137e2d7ff3e0571995070cc222 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -74,6 +74,7 @@ import net.minecraft.server.GroupDataEntity;
 import net.minecraft.server.IBlockData;
 import net.minecraft.server.IChunkAccess;
 import net.minecraft.server.IRegistry;
+import net.minecraft.server.MCUtil;
 import net.minecraft.server.MinecraftKey;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.MovingObjectPosition;
@@ -294,6 +295,7 @@ public class CraftWorld implements World {
         return ret;
     }
     public int getTileEntityCount() {
+        return MCUtil.ensureMain(() -> {
         // We don't use the full world tile entity list, so we must iterate chunks
         Long2ObjectLinkedOpenHashMap<PlayerChunk> chunks = world.getChunkProvider().playerChunkMap.visibleChunks;
         int size = 0;
@@ -305,11 +307,13 @@ public class CraftWorld implements World {
             size += chunk.tileEntities.size();
         }
         return size;
+        });
     }
     public int getTickableTileEntityCount() {
         return world.tileEntityListTick.size();
     }
     public int getChunkCount() {
+        return MCUtil.ensureMain(() -> {
         int ret = 0;
 
         for (PlayerChunk chunkHolder : world.getChunkProvider().playerChunkMap.visibleChunks.values()) {
@@ -318,7 +322,7 @@ public class CraftWorld implements World {
             }
         }
 
-        return ret;
+        return ret; });
     }
     public int getPlayerCount() {
         return world.players.size();
@@ -443,6 +447,14 @@ public class CraftWorld implements World {
 
     @Override
     public Chunk[] getLoadedChunks() {
+        // Paper start
+        if (Thread.currentThread() != world.getMinecraftWorld().serverThread) {
+            synchronized (world.getChunkProvider().playerChunkMap.visibleChunks) {
+                Long2ObjectLinkedOpenHashMap<PlayerChunk> chunks = world.getChunkProvider().playerChunkMap.visibleChunks;
+                return chunks.values().stream().map(PlayerChunk::getFullChunk).filter(Objects::nonNull).map(net.minecraft.server.Chunk::getBukkitChunk).toArray(Chunk[]::new);
+            }
+        }
+        // Paper end
         Long2ObjectLinkedOpenHashMap<PlayerChunk> chunks = world.getChunkProvider().playerChunkMap.visibleChunks;
         return chunks.values().stream().map(PlayerChunk::getFullChunk).filter(Objects::nonNull).map(net.minecraft.server.Chunk::getBukkitChunk).toArray(Chunk[]::new);
     }
