diff --git a/src/main/java/net/minestom/server/UpdateManager.java b/src/main/java/net/minestom/server/UpdateManager.java
index cbeb4ccb0..eb1842975 100644
--- a/src/main/java/net/minestom/server/UpdateManager.java
+++ b/src/main/java/net/minestom/server/UpdateManager.java
@@ -13,11 +13,11 @@ import net.minestom.server.thread.ThreadProvider;
 import net.minestom.server.utils.thread.MinestomThread;
 import net.minestom.server.utils.validate.Check;
 
-import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
-import java.util.function.Consumer;
+import java.util.function.DoubleConsumer;
 
 /**
  * Manager responsible for the server ticks.
@@ -36,8 +36,8 @@ public final class UpdateManager {
 
     private ThreadProvider threadProvider;
 
-    private final ArrayList<Runnable> tickStartCallbacks = new ArrayList<>();
-    private final ArrayList<Consumer<Double>> tickEndCallbacks = new ArrayList<>();
+    private final ConcurrentLinkedQueue<Runnable> tickStartCallbacks = new ConcurrentLinkedQueue<>();
+    private final ConcurrentLinkedQueue<DoubleConsumer> tickEndCallbacks = new ConcurrentLinkedQueue<>();
 
     {
         //threadProvider = new PerInstanceThreadProvider();
@@ -63,28 +63,33 @@ public final class UpdateManager {
             long currentTime;
             while (!stopRequested) {
                 currentTime = System.nanoTime();
-                final long time = System.currentTimeMillis();
+                final long tickStart = System.currentTimeMillis();
 
-                //Tick Callbacks
-                tickStartCallbacks.forEach(Runnable::run);
+                // Tick start callbacks
+                if (!tickStartCallbacks.isEmpty()) {
+                    Runnable callback;
+                    while ((callback = tickStartCallbacks.poll()) != null) {
+                        callback.run();
+                    }
+                }
 
                 List<Future<?>> futures;
 
                 // Server tick (instance/chunk/entity)
                 // Synchronize with the update manager instance, like the signal for chunk load/unload
                 synchronized (this) {
-                    futures = threadProvider.update(time);
+                    futures = threadProvider.update(tickStart);
                 }
 
                 // Waiting players update (newly connected clients waiting to get into the server)
                 entityManager.updateWaitingPlayers();
 
                 // Keep Alive Handling
-                final KeepAlivePacket keepAlivePacket = new KeepAlivePacket(time);
+                final KeepAlivePacket keepAlivePacket = new KeepAlivePacket(tickStart);
                 for (Player player : connectionManager.getOnlinePlayers()) {
-                    final long lastKeepAlive = time - player.getLastKeepAlive();
+                    final long lastKeepAlive = tickStart - player.getLastKeepAlive();
                     if (lastKeepAlive > KEEP_ALIVE_DELAY && player.didAnswerKeepAlive()) {
-                        player.refreshKeepAlive(time);
+                        player.refreshKeepAlive(tickStart);
                         player.getPlayerConnection().sendPacket(keepAlivePacket);
                     } else if (lastKeepAlive >= KEEP_ALIVE_KICK) {
                         player.kick(TIMEOUT_TEXT);
@@ -100,13 +105,17 @@ public final class UpdateManager {
                 }
 
 
-                //Tick Callbacks
-                double tickTime = (System.nanoTime() - currentTime) / 1000000D;
-                tickEndCallbacks.forEach(doubleConsumer -> doubleConsumer.accept(tickTime));
+                // Tick end callbacks
+                if (!tickEndCallbacks.isEmpty()) {
+                    final double tickEnd = (System.nanoTime() - currentTime) / 1000000D;
+                    DoubleConsumer callback;
+                    while ((callback = tickEndCallbacks.poll()) != null) {
+                        callback.accept(tickEnd);
+                    }
+                }
 
                 // Sleep until next tick
-                long sleepTime = (tickDistance - (System.nanoTime() - currentTime)) / 1000000;
-                sleepTime = Math.max(1, sleepTime);
+                final long sleepTime = Math.max(1, (tickDistance - (System.nanoTime() - currentTime)) / 1000000);
 
                 try {
                     Thread.sleep(sleepTime);
@@ -194,20 +203,42 @@ public final class UpdateManager {
         this.threadProvider.onChunkUnload(instance, chunkX, chunkZ);
     }
 
+    /**
+     * Adds a callback executed at the start of the next server tick.
+     *
+     * @param callback the tick start callback
+     */
     public void addTickStartCallback(Runnable callback) {
-        tickStartCallbacks.add(callback);
+        this.tickStartCallbacks.add(callback);
     }
 
+    /**
+     * Removes a tick start callback.
+     *
+     * @param callback the callback to remove
+     */
     public void removeTickStartCallback(Runnable callback) {
-        tickStartCallbacks.remove(callback);
+        this.tickStartCallbacks.remove(callback);
     }
 
-    public void addTickEndCallback(Consumer<Double> callback) {
-        tickEndCallbacks.add(callback);
+    /**
+     * Adds a callback executed at the end of the next server tick.
+     * <p>
+     * The double in the consumer represents the duration (in ms) of the tick.
+     *
+     * @param callback the tick end callback
+     */
+    public void addTickEndCallback(DoubleConsumer callback) {
+        this.tickEndCallbacks.add(callback);
     }
 
-    public void removeTickEndCallback(Consumer<Double> callback) {
-        tickEndCallbacks.remove(callback);
+    /**
+     * Removes a tick end callback.
+     *
+     * @param callback the callback to remove
+     */
+    public void removeTickEndCallback(DoubleConsumer callback) {
+        this.tickEndCallbacks.remove(callback);
     }
 
     /**
diff --git a/src/main/java/net/minestom/server/network/packet/client/handler/ClientPacketsHandler.java b/src/main/java/net/minestom/server/network/packet/client/handler/ClientPacketsHandler.java
index 02ae57eee..2b6650afd 100644
--- a/src/main/java/net/minestom/server/network/packet/client/handler/ClientPacketsHandler.java
+++ b/src/main/java/net/minestom/server/network/packet/client/handler/ClientPacketsHandler.java
@@ -9,9 +9,9 @@ public class ClientPacketsHandler {
     // Max packet id
     private static final int SIZE = 0x30;
 
-    private final Supplier<? extends ClientPacket>[] supplierAccesses = new Supplier[SIZE];
+    private final Supplier<ClientPacket>[] supplierAccesses = new Supplier[SIZE];
 
-    public void register(int id, Supplier<? extends ClientPacket> packetSupplier) {
+    public void register(int id, Supplier<ClientPacket> packetSupplier) {
         supplierAccesses[id] = packetSupplier;
     }
 
@@ -19,13 +19,13 @@ public class ClientPacketsHandler {
         if (id > SIZE)
             throw new IllegalStateException("Packet ID 0x" + Integer.toHexString(id) + " has been tried to be parsed, debug needed");
 
-        Supplier<? extends ClientPacket> supplier = supplierAccesses[id];
+        Supplier<ClientPacket> supplier = supplierAccesses[id];
         if (supplierAccesses[id] == null)
             throw new IllegalStateException("Packet id 0x" + Integer.toHexString(id) + " isn't registered!");
 
-        ClientPacket packet = supplier.get();
+        //ClientPacket packet = supplier.get();
         //System.out.println("RECEIVED PACKET 0x" + Integer.toHexString(id)+" : "+packet.getClass().getSimpleName());
-        return packet;
+        return supplier.get();
     }
 
 }
diff --git a/src/main/java/net/minestom/server/thread/ThreadProvider.java b/src/main/java/net/minestom/server/thread/ThreadProvider.java
index c3eed3bd9..0f5e1fa51 100644
--- a/src/main/java/net/minestom/server/thread/ThreadProvider.java
+++ b/src/main/java/net/minestom/server/thread/ThreadProvider.java
@@ -99,9 +99,7 @@ public abstract class ThreadProvider {
         this.pool = new MinestomThread(threadCount, MinecraftServer.THREAD_NAME_TICK);
     }
 
-    /**
-     * INSTANCE UPDATE
-     */
+    // INSTANCE UPDATE
 
     /**
      * Process a whole tick for a chunk.
@@ -146,9 +144,7 @@ public abstract class ThreadProvider {
         chunk.tick(time, instance);
     }
 
-    /**
-     * ENTITY UPDATE
-     */
+    // ENTITY UPDATE
 
     /**
      * Executes an entity tick (all entities type creatures/objects/players) in an instance's chunk.