Paper/patches/server/0396-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 530916b8d0c5eb3b7b379100df1e6e0d4ade273d..4d82abf234f67af124dff3f726a6a2e39313a780 100644
--- a/src/main/java/net/minecraft/server/MCUtil.java
+++ b/src/main/java/net/minecraft/server/MCUtil.java
@@ -614,7 +614,7 @@ public final class MCUtil {
 
             ServerLevel world = ((org.bukkit.craftbukkit.CraftWorld)bukkitWorld).getHandle();
             ChunkMap chunkMap = world.getChunkSource().chunkMap;
-            Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunks = chunkMap.visibleChunkMap;
+            Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunks = chunkMap.getVisibleChunks();
             DistanceManager chunkMapDistance = chunkMap.distanceManager;
             List<ChunkHolder> allChunks = new ArrayList<>(visibleChunks.values());
             List<ServerPlayer> players = world.players;
diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index f75a78f60565be1c8e8b0ce5f3937441f59e1f29..22f6898b96c68fa53ca5900985c18a6f2f5a8b57 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -112,9 +112,36 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     private static final int MIN_VIEW_DISTANCE = 3;
     public static final int MAX_VIEW_DISTANCE = 33;
     public static final int MAX_CHUNK_DISTANCE = 33 + ChunkStatus.maxDistance();
+    // Paper start - faster copying
+    public final Long2ObjectLinkedOpenHashMap<ChunkHolder> updatingChunkMap = new com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<>(); // Paper - faster copying
+    public final Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunkMap = new ProtectedVisibleChunksMap(); // Paper - faster copying
+
+    private class ProtectedVisibleChunksMap extends com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder> {
+        @Override
+        public ChunkHolder put(long k, ChunkHolder playerChunk) {
+            throw new UnsupportedOperationException("Updating visible Chunks");
+        }
+
+        @Override
+        public ChunkHolder remove(long k) {
+            throw new UnsupportedOperationException("Removing visible Chunks");
+        }
+
+        @Override
+        public ChunkHolder get(long k) {
+            return ChunkMap.this.getVisibleChunkIfPresent(k);
+        }
+
+        public ChunkHolder safeGet(long k) {
+            return super.get(k);
+        }
+    }
+    // Paper end
+    public final com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder> pendingVisibleChunks = new com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder>(); // Paper - this is used if the visible chunks is updated while iterating only
+    public transient com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder> visibleChunksClone; // Paper - used for async access of visible chunks, clone and cache only when needed
     public static final int FORCED_TICKET_LEVEL = 31;
-    public final Long2ObjectLinkedOpenHashMap<ChunkHolder> updatingChunkMap = new Long2ObjectLinkedOpenHashMap();
-    public volatile Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunkMap;
+    // public final Long2ObjectLinkedOpenHashMap<ChunkHolder> updatingChunkMap = new Long2ObjectLinkedOpenHashMap(); // Paper - moved up
+    // public volatile Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunkMap; // Paper - moved up
     private final Long2ObjectLinkedOpenHashMap<ChunkHolder> pendingUnloads;
     public final LongSet entitiesInLevel;
     public final ServerLevel level;
@@ -237,7 +264,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
     public ChunkMap(ServerLevel world, LevelStorageSource.LevelStorageAccess session, DataFixer dataFixer, StructureManager structureManager, Executor executor, BlockableEventLoop<Runnable> mainThreadExecutor, LightChunkGetter chunkProvider, ChunkGenerator chunkGenerator, ChunkProgressListener worldGenerationProgressListener, ChunkStatusUpdateListener chunkStatusChangeListener, Supplier<DimensionDataStorage> persistentStateManagerFactory, int viewDistance, boolean dsync) {
         super(new File(session.getDimensionPath(world.dimension()), "region"), dataFixer, dsync);
-        this.visibleChunkMap = this.updatingChunkMap.clone();
+        //this.visibleChunks = this.updatingChunks.clone(); // Paper - no more cloning
         this.pendingUnloads = new Long2ObjectLinkedOpenHashMap();
         this.entitiesInLevel = new LongOpenHashSet();
         this.toDrop = new LongOpenHashSet();
@@ -376,9 +403,52 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         return (ChunkHolder) this.updatingChunkMap.get(pos);
     }
 
+    // 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<ChunkHolder> consumer) {
+        org.spigotmc.AsyncCatcher.catchOp("forEachVisibleChunk");
+        boolean prev = isIterating;
+        isIterating = true;
+        try {
+            for (ChunkHolder value : this.visibleChunkMap.values()) {
+                consumer.accept(value);
+            }
+        } finally {
+            this.isIterating = prev;
+            if (!this.isIterating && this.hasPendingVisibleUpdate) {
+                ((ProtectedVisibleChunksMap)this.visibleChunkMap).copyFrom(this.pendingVisibleChunks);
+                this.pendingVisibleChunks.clear();
+                this.hasPendingVisibleUpdate = false;
+            }
+        }
+    }
+    public Long2ObjectLinkedOpenHashMap<ChunkHolder> getVisibleChunks() {
+        if (Thread.currentThread() == this.level.thread) {
+            return this.visibleChunkMap;
+        } else {
+            synchronized (this.visibleChunkMap) {
+                if (DEBUG_ASYNC_VISIBLE_CHUNKS) new Throwable("Async getVisibleChunks").printStackTrace();
+                if (this.visibleChunksClone == null) {
+                    this.visibleChunksClone = this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.clone() : ((ProtectedVisibleChunksMap)this.visibleChunkMap).clone();
+                }
+                return this.visibleChunksClone;
+            }
+        }
+    }
+    // Paper end
+
     @Nullable
     public ChunkHolder getVisibleChunkIfPresent(long pos) {
-        return (ChunkHolder) this.visibleChunkMap.get(pos);
+        // Paper start - mt safe get
+        if (Thread.currentThread() != this.level.thread) {
+            synchronized (this.visibleChunkMap) {
+                return (ChunkHolder) (this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.get(pos) : ((ProtectedVisibleChunksMap)this.visibleChunkMap).safeGet(pos));
+            }
+        }
+        return (ChunkHolder) (this.hasPendingVisibleUpdate ? this.pendingVisibleChunks.get(pos) : ((ProtectedVisibleChunksMap)this.visibleChunkMap).safeGet(pos));
+        // Paper end
     }
 
     protected IntSupplier getChunkQueueLevel(long pos) {
@@ -535,8 +605,9 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     }
 
     protected void saveAllChunks(boolean flush) {
+        Long2ObjectLinkedOpenHashMap<ChunkHolder> visibleChunks = this.getVisibleChunks(); // Paper remove clone of visible Chunks unless saving off main thread (watchdog kill)
         if (flush) {
-            List<ChunkHolder> list = (List) this.visibleChunkMap.values().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).peek(ChunkHolder::refreshAccessibility).collect(Collectors.toList());
+            List<ChunkHolder> list = (List) visibleChunks.values().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).peek(ChunkHolder::refreshAccessibility).collect(Collectors.toList()); // Paper - remove cloning of visible chunks
             MutableBoolean mutableboolean = new MutableBoolean();
 
             do {
@@ -567,7 +638,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 //            this.i(); // Paper - nuke IOWorker
             ChunkMap.LOGGER.info("ThreadedAnvilChunkStorage ({}): All chunks are saved", this.storageFolder.getName());
         } else {
-            this.visibleChunkMap.values().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).forEach((playerchunk) -> {
+            visibleChunks.values().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).forEach((playerchunk) -> {
                 ChunkAccess ichunkaccess = (ChunkAccess) playerchunk.getChunkToSave().getNow(null); // CraftBukkit - decompile error
 
                 if (ichunkaccess instanceof ImposterProtoChunk || ichunkaccess instanceof LevelChunk) {
@@ -725,7 +796,20 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         if (!this.modified) {
             return false;
         } else {
-            this.visibleChunkMap = this.updatingChunkMap.clone();
+            // Paper start - stop cloning visibleChunks
+            synchronized (this.visibleChunkMap) {
+                if (isIterating) {
+                    hasPendingVisibleUpdate = true;
+                    this.pendingVisibleChunks.copyFrom((com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder>)this.updatingChunkMap);
+                } else {
+                    hasPendingVisibleUpdate = false;
+                    this.pendingVisibleChunks.clear();
+                    ((ProtectedVisibleChunksMap)this.visibleChunkMap).copyFrom((com.destroystokyo.paper.util.map.Long2ObjectLinkedOpenHashMapFastCopy<ChunkHolder>)this.updatingChunkMap);
+                    this.visibleChunksClone = null;
+                }
+            }
+            // Paper end
+
             this.modified = false;
             return true;
         }
@@ -1172,12 +1256,12 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     }
 
     protected Iterable<ChunkHolder> getChunks() {
-        return Iterables.unmodifiableIterable(this.visibleChunkMap.values());
+        return Iterables.unmodifiableIterable(this.getVisibleChunks().values()); // Paper
     }
 
     void dumpChunks(Writer writer) throws IOException {
         CsvOutput csvwriter = CsvOutput.builder().addColumn("x").addColumn("z").addColumn("level").addColumn("in_memory").addColumn("status").addColumn("full_status").addColumn("accessible_ready").addColumn("ticking_ready").addColumn("entity_ticking_ready").addColumn("ticket").addColumn("spawning").addColumn("block_entity_count").build(writer);
-        ObjectBidirectionalIterator objectbidirectionaliterator = this.visibleChunkMap.long2ObjectEntrySet().iterator();
+        ObjectBidirectionalIterator objectbidirectionaliterator = this.getVisibleChunks().long2ObjectEntrySet().iterator(); // Paper
 
         while (objectbidirectionaliterator.hasNext()) {
             Entry<ChunkHolder> entry = (Entry) objectbidirectionaliterator.next();
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 43007f8cc9a88d7e6fb435551edac4d93a5668a9..6d999e0de0497114e46445981c64ee70f882c782 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -767,7 +767,7 @@ public class ServerChunkCache extends ChunkSource {
             };
             // Paper end
             this.level.timings.chunkTicks.startTiming(); // Paper
-            this.chunkMap.getChunks().forEach((playerchunk) -> { // Paper - no... just no...
+            this.chunkMap.forEachVisibleChunk((playerchunk) -> { // Paper - safe iterator incase chunk loads, also no wrapping
                 Optional<LevelChunk> optional = ((Either) playerchunk.getTickingChunkFuture().getNow(ChunkHolder.UNLOADED_LEVEL_CHUNK)).left();
 
                 if (optional.isPresent()) {
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index b6134895d1b04d3ea7340e77f70efa23cff8b568..72c9ad9f75c20d6c1a6d54e2913e2f9918c11ffd 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -287,6 +287,7 @@ public class CraftWorld implements World {
 
     @Override
     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<ChunkHolder> chunks = world.getChunkSource().chunkMap.visibleChunkMap;
         int size = 0;
@@ -298,6 +299,7 @@ public class CraftWorld implements World {
             size += chunk.blockEntities.size();
         }
         return size;
+        });
     }
 
     @Override
@@ -307,6 +309,7 @@ public class CraftWorld implements World {
 
     @Override
     public int getChunkCount() {
+        return net.minecraft.server.MCUtil.ensureMain(() -> {
         int ret = 0;
 
         for (ChunkHolder chunkHolder : world.getChunkSource().chunkMap.visibleChunkMap.values()) {
@@ -315,7 +318,7 @@ public class CraftWorld implements World {
             }
         }
 
-        return ret;
+        return ret; });
     }
 
     @Override
@@ -442,6 +445,14 @@ public class CraftWorld implements World {
 
     @Override
     public Chunk[] getLoadedChunks() {
+        // Paper start
+        if (Thread.currentThread() != world.getLevel().thread) {
+            synchronized (world.getChunkSource().chunkMap.visibleChunkMap) {
+                Long2ObjectLinkedOpenHashMap<ChunkHolder> chunks = world.getChunkSource().chunkMap.visibleChunkMap;
+                return chunks.values().stream().map(ChunkHolder::getFullChunk).filter(Objects::nonNull).map(net.minecraft.world.level.chunk.LevelChunk::getBukkitChunk).toArray(Chunk[]::new);
+            }
+        }
+        // Paper end
         Long2ObjectLinkedOpenHashMap<ChunkHolder> chunks = this.world.getChunkSource().chunkMap.visibleChunkMap;
         return chunks.values().stream().map(ChunkHolder::getFullChunk).filter(Objects::nonNull).map(net.minecraft.world.level.chunk.LevelChunk::getBukkitChunk).toArray(Chunk[]::new);
     }