Add thread checks for Window#open and Window#close

Author: NichtStudioCode

invui/src/main/java/xyz/xenondevs/invui/internal/menu/CustomContainerMenu.java

@@ -32,6 +32,7 @@
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
 import net.minecraft.world.item.component.BundleContents;
+import org.bukkit.Bukkit;
 import org.bukkit.craftbukkit.entity.CraftPlayer;
 import org.bukkit.craftbukkit.inventory.CraftInventory;
 import org.bukkit.craftbukkit.inventory.CraftItemStack;
@@ -146,6 +147,8 @@ public Integer apply(TypedDataComponent<?> tdc) {
 
         @Override
         public Integer apply(TypedDataComponent<?> tdc) {
+            assert Bukkit.isOwnedByCurrentRegion(player);
+            
             var c = tdc.value();
             var cachedValue = cache.get(c);
             if (cachedValue.isPresent())

invui/src/main/java/xyz/xenondevs/invui/internal/util/ThreadCheck.java

@@ -0,0 +1,20 @@
+package xyz.xenondevs.invui.internal.util;
+
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
+
+public class ThreadCheck {
+    
+    public static void checkOwnedBy(Entity entity) {
+        if (Bukkit.isOwnedByCurrentRegion(entity))
+            return;
+        
+        throw new IllegalArgumentException(
+            "A method was called from an incorrect thread. On Paper the correct thread is the server thread. " +
+            "On Folia, the correct thread is the thread that owns the viewer (use the viewer's entity scheduler). " +
+            "Note that the absence of this exception does not imply correctness. In general and unless otherwise documented, " +
+            "nothing in InvUI is thread-safe and all methods should be called from the corresponding viewer's thread."
+        );
+    }
+    
+}

invui/src/main/java/xyz/xenondevs/invui/window/AbstractWindow.java

@@ -26,10 +26,7 @@
 import xyz.xenondevs.invui.internal.menu.CustomContainerMenu;
 import xyz.xenondevs.invui.internal.menu.UpdateType;
 import xyz.xenondevs.invui.internal.menu.WindowEventListener;
-import xyz.xenondevs.invui.internal.util.CollectionUtils;
-import xyz.xenondevs.invui.internal.util.FakeInventoryView;
-import xyz.xenondevs.invui.internal.util.FuncUtils;
-import xyz.xenondevs.invui.internal.util.InventoryUtils;
+import xyz.xenondevs.invui.internal.util.*;
 import xyz.xenondevs.invui.inventory.CompositeInventory;
 import xyz.xenondevs.invui.inventory.Inventory;
 import xyz.xenondevs.invui.inventory.InventorySlot;
@@ -504,6 +501,7 @@ public void open() {
             throw new IllegalStateException("Opening a window is not allowed to trigger opening another window.");
         if (isInCloseHandlerContext.get() > 0)
             throw new IllegalStateException("Opening a window is not allowed while handling window close. Consider setting a fallback window or scheduling a task instead.");
+        ThreadCheck.checkOwnedBy(viewer);
 
         try {
             isInOpeningContext.set(true);
@@ -549,6 +547,7 @@ protected void postItemInit() {
 
     @Override
     public void close() {
+        ThreadCheck.checkOwnedBy(getViewer());
         if (isOpen()) {
             viewer.closeInventory(); // WindowManager then calls handleClose
         }