Cache the unmodifiable viewers set to mitigate object allocation

src/main/java/net/minestom/server/bossbar/BossBar.java

@@ -27,6 +27,7 @@ public class BossBar implements Viewable {
 
     private final UUID uuid = UUID.randomUUID();
     private final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
 
     private ColoredText title;
     private float progress;
@@ -89,7 +90,7 @@ public class BossBar implements Viewable {
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(viewers);
+        return unmodifiableViewers;
     }
 
     /**

src/main/java/net/minestom/server/entity/Entity.java

@@ -93,6 +93,7 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
     private boolean autoViewable;
     private final int id;
     protected final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
     private Data data;
     private final Set<Permission> permissions = new CopyOnWriteArraySet<>();
 
@@ -325,7 +326,7 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(viewers);
+        return unmodifiableViewers;
     }
 
     @Override

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

@@ -76,6 +76,7 @@ public abstract class Chunk implements Viewable, DataContainer {
 
     protected volatile boolean loaded = true;
     protected final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
 
     // Path finding
     protected PFColumnarSpace columnarSpace;
@@ -489,7 +490,7 @@ public abstract class Chunk implements Viewable, DataContainer {
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(viewers);
+        return unmodifiableViewers;
     }
 
     @Nullable

src/main/java/net/minestom/server/inventory/Inventory.java

@@ -58,6 +58,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
     private final ItemStack[] itemStacks;
     // the players currently viewing this inventory
     private final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
     // (player -> cursor item) map, used by the click listeners
     private final ConcurrentHashMap<Player, ItemStack> cursorPlayersItem = new ConcurrentHashMap<>();
 
@@ -251,7 +252,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(viewers);
+        return unmodifiableViewers;
     }
 
     /**

src/main/java/net/minestom/server/scoreboard/BelowNameTag.java

@@ -10,7 +10,7 @@ import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 
 /**
- * Represents a scoreboard which rendered a tag below the name
+ * Represents a scoreboard which rendered a tag below the name.
  */
 public class BelowNameTag implements Scoreboard {
 
@@ -20,12 +20,13 @@ public class BelowNameTag implements Scoreboard {
     public static final String BELOW_NAME_TAG_PREFIX = "bnt-";
 
     private final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
     private final String objectiveName;
 
     private final ScoreboardObjectivePacket scoreboardObjectivePacket;
 
     /**
-     * Creates a new below name scoreboard
+     * Creates a new below name scoreboard.
      *
      * @param name  The objective name of the scoreboard
      * @param value The value of the scoreboard
@@ -72,6 +73,6 @@ public class BelowNameTag implements Scoreboard {
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(viewers);
+        return unmodifiableViewers;
     }
 }

src/main/java/net/minestom/server/scoreboard/Sidebar.java

@@ -14,6 +14,7 @@ import net.minestom.server.utils.validate.Check;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.Queue;
 import java.util.Set;
@@ -46,6 +47,7 @@ public class Sidebar implements Scoreboard {
     private static final int MAX_LINES_COUNT = 15;
 
     private final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
 
     private final Queue<ScoreboardLine> lines = Queues.newConcurrentLinkedQueue();
     private final IntLinkedOpenHashSet availableColors = new IntLinkedOpenHashSet();
@@ -218,7 +220,7 @@ public class Sidebar implements Scoreboard {
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return viewers;
+        return unmodifiableViewers;
     }
 
     @Override

src/main/java/net/minestom/server/scoreboard/TabList.java

@@ -10,7 +10,7 @@ import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 
 /**
- * Represents the {@link Player} tab list as a {@link Scoreboard}
+ * Represents the {@link Player} tab list as a {@link Scoreboard}.
  */
 public class TabList implements Scoreboard {
 
@@ -19,13 +19,13 @@ public class TabList implements Scoreboard {
      */
     private static final String TAB_LIST_PREFIX = "tl-";
 
-    private final Set<Player> viewers;
+    private final Set<Player> viewers = new CopyOnWriteArraySet<>();
+    private final Set<Player> unmodifiableViewers = Collections.unmodifiableSet(viewers);
     private final String objectiveName;
 
     private ScoreboardObjectivePacket.Type type;
 
     public TabList(String name, ScoreboardObjectivePacket.Type type) {
-        this.viewers = new CopyOnWriteArraySet<>();
         this.objectiveName = TAB_LIST_PREFIX + name;
 
         this.type = type;
@@ -77,7 +77,7 @@ public class TabList implements Scoreboard {
     @NotNull
     @Override
     public Set<Player> getViewers() {
-        return Collections.unmodifiableSet(this.viewers);
+        return unmodifiableViewers;
     }
 
     @Override