From f36a8f4266355aea3d365ea867925713f6815f09 Mon Sep 17 00:00:00 2001
From: embeddedt <42941056+embeddedt@users.noreply.github.com>
Date: Sun, 16 Apr 2023 11:39:54 -0400
Subject: [PATCH] Clear ObjectHolder Throwable fields after registry events
 fire

---
 .../org/embeddedt/modernfix/ModernFix.java    |  3 +-
 .../registry/ObjectHolderClearer.java         | 47 +++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 src/main/java/org/embeddedt/modernfix/registry/ObjectHolderClearer.java

diff --git a/src/main/java/org/embeddedt/modernfix/ModernFix.java b/src/main/java/org/embeddedt/modernfix/ModernFix.java
index bf73fc45..f1106e64 100644
--- a/src/main/java/org/embeddedt/modernfix/ModernFix.java
+++ b/src/main/java/org/embeddedt/modernfix/ModernFix.java
@@ -18,6 +18,7 @@ import org.apache.logging.log4j.Logger;
 import org.embeddedt.modernfix.core.config.ModernFixConfig;
 import org.embeddedt.modernfix.entity.EntityDataIDSyncHandler;
 import org.embeddedt.modernfix.packet.PacketHandler;
+import org.embeddedt.modernfix.registry.ObjectHolderClearer;
 import org.embeddedt.modernfix.structure.AsyncLocator;
 import org.embeddedt.modernfix.util.KubeUtil;
 
@@ -91,7 +92,7 @@ public class ModernFix {
                 ModLoader.get().addWarning(new ModLoadingWarning(ModLoadingContext.get().getActiveContainer().getModInfo(), ModLoadingStage.COMMON_SETUP, "modernfix.no_lazydfu"));
             });
         }
-
+        ObjectHolderClearer.clearThrowables();
     }
 
     @SubscribeEvent
diff --git a/src/main/java/org/embeddedt/modernfix/registry/ObjectHolderClearer.java b/src/main/java/org/embeddedt/modernfix/registry/ObjectHolderClearer.java
new file mode 100644
index 00000000..6ca0f948
--- /dev/null
+++ b/src/main/java/org/embeddedt/modernfix/registry/ObjectHolderClearer.java
@@ -0,0 +1,47 @@
+package org.embeddedt.modernfix.registry;
+
+import net.minecraft.resources.ResourceLocation;
+import net.minecraftforge.fml.common.ObfuscationReflectionHelper;
+import net.minecraftforge.registries.ObjectHolderRegistry;
+import org.embeddedt.modernfix.ModernFix;
+
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+public class ObjectHolderClearer {
+    /**
+     * Many of the built-in Forge holders needlessly hold on to an exception.
+     */
+    public static void clearThrowables() {
+        Set<Consumer<Predicate<ResourceLocation>>> holders = ObfuscationReflectionHelper.getPrivateValue(ObjectHolderRegistry.class, null, "objectHolders");
+        if(holders != null) {
+            int numCleared = 0;
+            HashMap<Class<?>, Field> throwableField = new HashMap<>();
+            Throwable singletonThrowable = new Throwable("[This stacktrace was cleared to save memory]");
+            try {
+                for(Consumer<Predicate<ResourceLocation>> holder : holders) {
+                    Field target = throwableField.computeIfAbsent(holder.getClass(), clz -> {
+                        Field[] clzFields = clz.getDeclaredFields();
+                        for(Field f : clzFields) {
+                            if(Throwable.class.isAssignableFrom(f.getType())) {
+                                f.setAccessible(true);
+                                return f;
+                            }
+                        }
+                        return null;
+                    });
+                    if(target != null) {
+                        target.set(holder, singletonThrowable);
+                        numCleared++;
+                    }
+                }
+            } catch(RuntimeException | ReflectiveOperationException | NoClassDefFoundError ignored) {
+            }
+            ModernFix.LOGGER.debug("Cleared " + numCleared + " object holder stacktrace references");
+        }
+    }
+}