WIP chunk saving optimization

src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/skip_redundant_saves/ChunkHolderMixin.java

@@ -0,0 +1,27 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.skip_redundant_saves;
+
+import com.llamalad7.mixinextras.injector.v2.WrapWithCondition;
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.LevelChunk;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+
+import javax.annotation.Nullable;
+
+@Mixin(ChunkHolder.class)
+public abstract class ChunkHolderMixin {
+    @Shadow
+    @Nullable
+    public abstract LevelChunk getTickingChunk();
+
+    /**
+     * @author embeddedt
+     * @reason prevent chunks from being flagged for saving when light engine is loading data from disk
+     */
+    @WrapWithCondition(method = "sectionLightChanged", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/level/chunk/ChunkAccess;setUnsaved(Z)V"))
+    private boolean onlyMarkUnsavedIfAlreadyTicking(ChunkAccess instance, boolean unsaved) {
+        return this.getTickingChunk() != null;
+    }
+}

src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/skip_redundant_saves/ChunkMapAccessor.java

@@ -0,0 +1,12 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.skip_redundant_saves;
+
+import net.minecraft.server.level.ChunkMap;
+import net.minecraft.world.level.ChunkPos;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Invoker;
+
+@Mixin(ChunkMap.class)
+public interface ChunkMapAccessor {
+    @Invoker("releaseLightTicket")
+    void mfix$invokeReleaseLightTicket(ChunkPos pos);
+}

src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/skip_redundant_saves/ChunkSerializerMixin.java

@@ -0,0 +1,26 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.skip_redundant_saves;
+
+import com.llamalad7.mixinextras.sugar.Local;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.entity.ai.village.poi.PoiManager;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ProtoChunk;
+import net.minecraft.world.level.chunk.storage.ChunkSerializer;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(ChunkSerializer.class)
+public class ChunkSerializerMixin {
+    /**
+     * @author embeddedt
+     * @reason When reloading chunks from disk, they by definition normally don't need saving unless they've changed.
+     */
+    @Inject(method = "read", at = @At(value = "CONSTANT", args = "stringValue=PostProcessing", ordinal = 0))
+    private static void updateUnsavedFlag(ServerLevel level, PoiManager poiManager, ChunkPos pos, CompoundTag tag, CallbackInfoReturnable<ProtoChunk> cir, @Local(ordinal = 0) ChunkAccess chunkaccess) {
+        chunkaccess.setUnsaved(tag.getBoolean("shouldSave"));
+    }
+}

src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/skip_redundant_saves/ThreadedLevelLightEngineMixin.java

@@ -0,0 +1,36 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.skip_redundant_saves;
+
+import net.minecraft.server.level.ChunkMap;
+import net.minecraft.server.level.ThreadedLevelLightEngine;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import org.spongepowered.asm.mixin.Final;
+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.CallbackInfoReturnable;
+
+import java.util.concurrent.CompletableFuture;
+
+@Mixin(ThreadedLevelLightEngine.class)
+public class ThreadedLevelLightEngineMixin {
+    @Shadow
+    @Final
+    private ChunkMap chunkMap;
+
+    /**
+     * @author embeddedt
+     * @reason avoid toggling the lightCorrect flag when chunk is already lit, because it triggers saving
+     */
+    @Inject(method = "lightChunk", at = @At("HEAD"), cancellable = true)
+    private void skipLightCorrectFlagChange(ChunkAccess chunk, boolean isAlreadyLit, CallbackInfoReturnable<CompletableFuture<ChunkAccess>> cir) {
+        if (isAlreadyLit) {
+            ((ChunkMapAccessor)this.chunkMap).mfix$invokeReleaseLightTicket(chunk.getPos());
+            // Defensively ensure the lightCorrect flag is set properly on exit from this method
+            if (!chunk.isLightCorrect()) {
+                chunk.setLightCorrect(true);
+            }
+            cir.setReturnValue(CompletableFuture.completedFuture(chunk));
+        }
+    }
+}

src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java

@@ -184,6 +184,7 @@ public class ModernFixEarlyConfig {
             .put("mixin.feature.spam_thread_dump", false)
             .put("mixin.feature.disable_unihex_font", false)
             .put("mixin.feature.remove_chat_signing", false)
+            .put("mixin.bugfix.skip_redundant_saves", false)
             .put("mixin.feature.snapshot_easter_egg", true)
             .put("mixin.feature.warn_missing_perf_mods", true)
             .put("mixin.feature.spark_profile_launch", false)