Forced save instead of chunk unloading

SpigotCore_14/src/de/steamwar/core/FlatteningWrapper14.java

@@ -23,6 +23,7 @@ import com.comphenix.tinyprotocol.Reflection;
 import org.bukkit.Bukkit;
 import org.bukkit.Material;
 import org.bukkit.NamespacedKey;
+import org.bukkit.World;
 import org.bukkit.entity.EntityType;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
@@ -350,4 +351,11 @@ public class FlatteningWrapper14 implements FlatteningWrapper.IFlatteningWrapper
     public int getViewDistance(Player player) {
         return player.getClientViewDistance();
     }
+
+    private static final Reflection.MethodInvoker getHandle = Reflection.getMethod("{obc}.CraftWorld", "getHandle");
+    private static final Reflection.MethodInvoker save = Reflection.getMethod("{nms.server.level}.WorldServer", null, Reflection.getClass("{nms.util}.IProgressUpdate"), boolean.class, boolean.class);
+    @Override
+    public void syncSave(World world) {
+        save.invoke(getHandle.invoke(world), null, true, false);
+    }
 }

SpigotCore_8/src/de/steamwar/core/FlatteningWrapper8.java

@@ -21,6 +21,7 @@ package de.steamwar.core;
 
 import com.comphenix.tinyprotocol.Reflection;
 import org.bukkit.Material;
+import org.bukkit.World;
 import org.bukkit.entity.EntityType;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
@@ -111,4 +112,10 @@ public class FlatteningWrapper8 implements FlatteningWrapper.IFlatteningWrapper
     public int getViewDistance(Player player) {
         return 10;
     }
+
+    private static final Reflection.MethodInvoker save = Reflection.getMethod("{obc}.CraftWorld", "save", boolean.class);
+    @Override
+    public void syncSave(World world) {
+        save.invoke(world, true);
+    }
 }

SpigotCore_Main/src/de/steamwar/core/CheckpointUtils.java

@@ -25,17 +25,17 @@ import com.viaversion.viaversion.api.Via;
 import de.steamwar.sql.internal.Statement;
 import io.netty.channel.ChannelFuture;
 import org.bukkit.Bukkit;
-import org.bukkit.Chunk;
 import org.eclipse.openj9.criu.CRIUSupport;
 import org.eclipse.openj9.criu.JVMCRIUException;
 import sun.misc.Signal;
 
-import java.io.*;
+import java.io.DataInputStream;
+import java.io.File;
+import java.io.IOException;
 import java.net.InetAddress;
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
 import java.util.logging.Level;
@@ -84,7 +84,7 @@ public class CheckpointUtils {
     private static final Reflection.FieldAccessor<List> channelFutures = Reflection.getField(TinyProtocol.serverConnection, List.class, 0, ChannelFuture.class);
     private static final Reflection.MethodInvoker bind = Reflection.getMethod(TinyProtocol.serverConnection, null, InetAddress.class, int.class);
     private static void freezeInternal(Path path) throws Exception {
-        Bukkit.getWorlds().forEach(world -> Arrays.stream(world.getLoadedChunks()).forEach(Chunk::unload));
+        Bukkit.getWorlds().forEach(FlatteningWrapper.impl::syncSave);
         Statement.closeAll();
 
         // Close socket
@@ -96,6 +96,9 @@ public class CheckpointUtils {
         }
         channels.clear();
 
+        System.runFinalization();
+        System.gc();
+
         // Do the checkpoint
         path.toFile().mkdirs();
         CRIUSupport criu = new CRIUSupport(path);

SpigotCore_Main/src/de/steamwar/core/FlatteningWrapper.java

@@ -21,6 +21,7 @@ package de.steamwar.core;
 
 import com.comphenix.tinyprotocol.Reflection;
 import org.bukkit.Material;
+import org.bukkit.World;
 import org.bukkit.entity.EntityType;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
@@ -48,6 +49,8 @@ public class FlatteningWrapper {
         void setSpawnPacketType(Object packet, EntityType type);
 
         int getViewDistance(Player player);
+
+        void syncSave(World world);
     }
 
     public enum EntityPose {