Paper/Spigot-Server-Patches/0428-Optimize-PlayerChunkMap-memory-use-for-visibleChunks.patch

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/MCUtil.java b/src/main/java/net/minecraft/server/MCUtil.java
index 5a410550cfb48505c9de9979465ed1528c8fbf05..9edbde8299bcd127e1727d34ed441f638e716b2a 100644
--- a/src/main/java/net/minecraft/server/MCUtil.java
+++ b/src/main/java/net/minecraft/server/MCUtil.java
@@ -616,7 +616,7 @@ 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/level/ChunkProviderServer.java b/src/main/java/net/minecraft/server/level/ChunkProviderServer.java
index 911b733d32400a6f963a20f10de3802e70dd8823..af6309899dcb4fe09b765bf1073e482d16b0fb24 100644
--- a/src/main/java/net/minecraft/server/level/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/level/ChunkProviderServer.java
@@ -780,7 +780,7 @@ 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/level/PlayerChunkMap.java b/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
index 12cfe9f3c89316557e94c8b944b4f82277fb8877..8050be2ed04fb0b8141f92595680407bba65dad5 100644
--- a/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
@@ -106,8 +106,33 @@ 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;
     public final LongSet loadedChunks; // Paper - private -> public
     public final WorldServer world;
@@ -180,7 +205,7 @@ 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();
@@ -272,9 +297,52 @@ 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) {
@@ -462,8 +530,9 @@ 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 {
@@ -491,7 +560,7 @@ 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) {
@@ -662,7 +731,20 @@ 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;
         }
@@ -1133,12 +1215,12 @@ 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 cc15f27759771c0d839dcc7118ed898cf3617619..da3c7aaf6c2732450ac365c11a1fd7b70db0513d 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -294,6 +294,7 @@ public class CraftWorld implements World {
         return ret;
     }
     public int getTileEntityCount() {
+        return net.minecraft.server.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 +306,13 @@ public class CraftWorld implements World {
             size += chunk.tileEntities.size();
         }
         return size;
+        });
     }
     public int getTickableTileEntityCount() {
         return world.tileEntityListTick.size();
     }
     public int getChunkCount() {
+        return net.minecraft.server.MCUtil.ensureMain(() -> {
         int ret = 0;
 
         for (PlayerChunk chunkHolder : world.getChunkProvider().playerChunkMap.visibleChunks.values()) {
@@ -318,7 +321,7 @@ public class CraftWorld implements World {
             }
         }
 
-        return ret;
+        return ret; });
     }
     public int getPlayerCount() {
         return world.players.size();
@@ -443,6 +446,14 @@ 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.world.level.chunk.Chunk::getBukkitChunk).toArray(Chunk[]::new);
     }