Mitigation for memory usage from leaked client worlds

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/world_leaks/MinecraftMixin.java

@@ -0,0 +1,41 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.world_leaks;
+
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.multiplayer.ClientLevel;
+import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraft.world.level.lighting.LevelLightEngine;
+import org.embeddedt.modernfix.ModernFix;
+import org.jetbrains.annotations.Nullable;
+import org.objectweb.asm.Opcodes;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import java.util.concurrent.atomic.AtomicReferenceArray;
+
+@Mixin(Minecraft.class)
+public class MinecraftMixin {
+    @Shadow @Nullable public ClientLevel level;
+
+    /**
+     * To mitigate the effect of leaked client worlds, clear most of the data structures that waste memory.
+     */
+    @Inject(method = "clearLevel(Lnet/minecraft/client/gui/screens/Screen;)V", at = @At(value = "FIELD", opcode = Opcodes.PUTFIELD, target = "Lnet/minecraft/client/Minecraft;level:Lnet/minecraft/client/multiplayer/ClientLevel;"))
+    private void clearLevelDataForLeaks(CallbackInfo ci) {
+        if(this.level != null) {
+            try {
+                AtomicReferenceArray<LevelChunk> chunks = this.level.getChunkSource().storage.chunks;
+                for(int i = 0; i < chunks.length(); i++) {
+                    chunks.set(i, null);
+                }
+                this.level.getChunkSource().lightEngine = new LevelLightEngine(this.level.getChunkSource(), false, false);
+                // clear BE list otherwise they will hold chunks
+                this.level.blockEntityList.clear();
+            } catch(RuntimeException e) {
+                ModernFix.LOGGER.error("Exception clearing level data", e);
+            }
+        }
+    }
+}

common/src/main/resources/modernfix.accesswidener

@@ -1,5 +1,11 @@
 accessWidener   v2  named
 
+accessible field net/minecraft/client/multiplayer/ClientChunkCache storage Lnet/minecraft/client/multiplayer/ClientChunkCache$Storage;
+accessible field net/minecraft/client/multiplayer/ClientChunkCache lightEngine Lnet/minecraft/world/level/lighting/LevelLightEngine;
+mutable field net/minecraft/client/multiplayer/ClientChunkCache lightEngine Lnet/minecraft/world/level/lighting/LevelLightEngine;
+accessible class net/minecraft/client/multiplayer/ClientChunkCache$Storage
+accessible field net/minecraft/client/multiplayer/ClientChunkCache$Storage chunks Ljava/util/concurrent/atomic/AtomicReferenceArray;
+
 accessible class net/minecraft/client/renderer/RenderType$CompositeRenderType
 accessible method net/minecraft/client/renderer/RenderType$CompositeRenderType <init> (Ljava/lang/String;Lcom/mojang/blaze3d/vertex/VertexFormat;IIZZLnet/minecraft/client/renderer/RenderType$CompositeState;)V
 accessible method net/minecraft/nbt/CompoundTag <init> (Ljava/util/Map;)V