[ci skip] Avoid call currentThread() twice on ensures pakcet safety

src/main/java/net/minecraft/server/IAsyncTaskHandler.java

@@ -0,0 +1,15 @@
+package net.minecraft.server;
+
+import com.google.common.util.concurrent.ListenableFuture;
+
+public interface IAsyncTaskHandler {
+
+    ListenableFuture<Object> postToMainThread(Runnable runnable);
+
+    boolean isMainThread();
+    // Akarin start
+    public default void ensuresMainThread(Runnable runnable) {
+        postToMainThread(runnable);
+    }
+    // Akarin end
+}

src/main/java/net/minecraft/server/MinecraftServer.java

@@ -1681,7 +1681,7 @@ public abstract class MinecraftServer implements IAsyncTaskHandler, IMojangStati
         if (!this.isMainThread()) { // CraftBukkit && !this.isStopped()) {
             ListenableFutureTask<V> listenablefuturetask = ListenableFutureTask.create(callable);
 
-            this.f.add(listenablefuturetask);
+            this.f.offer(listenablefuturetask); // Akarin - add -> offer
             return listenablefuturetask;
         } else {
             try {
@@ -1691,6 +1691,12 @@ public abstract class MinecraftServer implements IAsyncTaskHandler, IMojangStati
             }
         }
     }
+    // Akarin start
+    @Override
+    public void ensuresMainThread(Runnable runnable) {
+        this.f.offer(ListenableFutureTask.create(runnable, null));
+    }
+    // Akarin end
 
     public ListenableFuture<Object> postToMainThread(Runnable runnable) {
         Validate.notNull(runnable);

src/main/java/net/minecraft/server/PlayerConnectionUtils.java

@@ -9,7 +9,7 @@ public class PlayerConnectionUtils {
         if (!iasynctaskhandler.isMainThread()) {
             Timing timing = MinecraftTimings.getPacketTiming(packet); // Paper
 
-            iasynctaskhandler.postToMainThread(() -> {
+            iasynctaskhandler.ensuresMainThread(() -> {
                 if (t0 instanceof PlayerConnection && ((PlayerConnection) t0).processedDisconnect) return; // CraftBukkit
                 try (Timing ignored = timing.startTiming()) { // Paper
                 packet.a(t0);

src/main/java/net/minecraft/server/WorldServer.java

@@ -4,6 +4,8 @@ import co.aikar.timings.Timings;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListenableFutureTask;
+
 import it.unimi.dsi.fastutil.objects.ObjectLinkedOpenHashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -1269,6 +1271,12 @@ public class WorldServer extends World implements IAsyncTaskHandler {
     public ListenableFuture<Object> postToMainThread(Runnable runnable) {
         return this.server.postToMainThread(runnable);
     }
+    // Akarin start
+    @Override
+    public void ensuresMainThread(Runnable runnable) {
+        this.server.f.offer(ListenableFutureTask.create(runnable, null));
+    }
+    // Akarin end
 
     public boolean isMainThread() {
         return this.server.isMainThread();