Reduced the number of garbage objects

src/main/java/net/minestom/server/instance/Chunk.java

@@ -38,6 +38,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
 /**
  * A chunk is a part of an {@link Instance}, limited by a size of 16x256x16 blocks and subdivided in 16 sections of 16 blocks height.
  * Should contains all the blocks located at those positions and manage their tick updates.
+ * Be aware that implementations do not need to be thread-safe.
  * <p>
  * Chunks can be serialized using {@link #getSerializedData()} and deserialized back with {@link #readChunk(BinaryReader, ChunkCallback)},
  * allowing you to implement your own storage solution if needed.

src/main/java/net/minestom/server/instance/DynamicChunk.java

@@ -30,6 +30,8 @@ import java.util.Set;
 
 /**
  * Represents a {@link Chunk} which store each individual block in memory.
+ * <p>
+ * WARNING: not thread-safe
  */
 public class DynamicChunk extends Chunk {
 

src/main/java/net/minestom/server/instance/Instance.java

@@ -1,5 +1,7 @@
 package net.minestom.server.instance;
 
+import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.UpdateManager;
 import net.minestom.server.data.Data;
@@ -79,7 +81,7 @@ public abstract class Instance implements BlockModifier, EventHandler, DataConta
     protected final Set<ObjectEntity> objectEntities = new CopyOnWriteArraySet<>();
     protected final Set<ExperienceOrb> experienceOrbs = new CopyOnWriteArraySet<>();
     // Entities per chunk
-    protected final Map<Long, Set<Entity>> chunkEntities = new ConcurrentHashMap<>();
+    protected final Long2ObjectMap<Set<Entity>> chunkEntities = new Long2ObjectOpenHashMap<>();
 
     // the uuid of this instance
     protected UUID uniqueId;
@@ -971,8 +973,10 @@ public abstract class Instance implements BlockModifier, EventHandler, DataConta
 
     @NotNull
     private Set<Entity> getEntitiesInChunk(long index) {
+        synchronized (chunkEntities) {
             return chunkEntities.computeIfAbsent(index, i -> new CopyOnWriteArraySet<>());
         }
+    }
 
     /**
      * Schedules a block update at a given {@link BlockPosition}.

src/main/java/net/minestom/server/instance/InstanceContainer.java

@@ -1,5 +1,7 @@
 package net.minestom.server.instance;
 
+import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.data.Data;
 import net.minestom.server.data.SerializableData;
@@ -33,7 +35,6 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.*;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReadWriteLock;
@@ -56,7 +57,7 @@ public class InstanceContainer extends Instance {
     // the chunk generator used, can be null
     private ChunkGenerator chunkGenerator;
     // (chunk index -> chunk) map, contains all the chunks in the instance
-    private final ConcurrentHashMap<Long, Chunk> chunks = new ConcurrentHashMap<>();
+    private final Long2ObjectMap<Chunk> chunks = new Long2ObjectOpenHashMap<>();
     // contains all the chunks to remove during the next instance tick
     protected final Set<Chunk> scheduledChunksToRemove = new HashSet<>();
 
@@ -450,9 +451,11 @@ public class InstanceContainer extends Instance {
     @Override
     public Chunk getChunk(int chunkX, int chunkZ) {
         final long index = ChunkUtils.getChunkIndex(chunkX, chunkZ);
+        synchronized (chunks) {
             final Chunk chunk = chunks.get(index);
             return ChunkUtils.isLoaded(chunk) ? chunk : null;
         }
+    }
 
     /**
      * Saves the instance ({@link #getUniqueId()} {@link #getData()}) and call {@link #saveChunksToStorage(Runnable)}.
@@ -492,7 +495,10 @@ public class InstanceContainer extends Instance {
 
     @Override
     public void saveChunksToStorage(@Nullable Runnable callback) {
-        this.chunkLoader.saveChunks(chunks.values(), callback);
+        synchronized (chunks) {
+            Collection<Chunk> chunksCollection = chunks.values();
+            this.chunkLoader.saveChunks(chunksCollection, callback);
+        }
     }
 
     @Override
@@ -639,6 +645,7 @@ public class InstanceContainer extends Instance {
         copiedInstance.srcInstance = this;
         copiedInstance.lastBlockChangeTime = lastBlockChangeTime;
 
+        synchronized (chunks) {
             for (Chunk chunk : chunks.values()) {
                 final int chunkX = chunk.getChunkX();
                 final int chunkZ = chunk.getChunkZ();
@@ -648,6 +655,7 @@ public class InstanceContainer extends Instance {
                 copiedInstance.cacheChunk(copiedChunk);
                 UPDATE_MANAGER.signalChunkLoad(copiedInstance, chunkX, chunkZ);
             }
+        }
 
         return copiedInstance;
     }
@@ -693,8 +701,10 @@ public class InstanceContainer extends Instance {
      */
     public void cacheChunk(@NotNull Chunk chunk) {
         final long index = ChunkUtils.getChunkIndex(chunk.getChunkX(), chunk.getChunkZ());
+        synchronized (chunks) {
             this.chunks.put(index, chunk);
         }
+    }
 
     @Override
     public ChunkGenerator getChunkGenerator() {
@@ -823,8 +833,12 @@ public class InstanceContainer extends Instance {
                 });
 
                 // Clear cache
+                synchronized (chunks) {
                     this.chunks.remove(index);
+                }
+                synchronized (chunkEntities) {
                     this.chunkEntities.remove(index);
+                }
 
                 chunk.unload();