Enforce Sync Player Saves

Saving players async is extremely dangerous. This will force it to main
the same way we handle async chunk loads.

paper-server/patches/sources/net/minecraft/server/players/PlayerList.java.patch

@@ -729,10 +729,14 @@
              this.sendAllPlayerInfoIn = 0;
          }
  
-@@ -541,6 +836,25 @@
+@@ -537,9 +832,28 @@
- 
+             ServerPlayer entityplayer = (ServerPlayer) iterator.next();
-     }
  
+             entityplayer.connection.send(packet);
++        }
++
++    }
++
 +    // CraftBukkit start - add a world/entity limited version
 +    public void broadcastAll(Packet packet, net.minecraft.world.entity.player.Player entityhuman) {
 +        for (int i = 0; i < this.players.size(); ++i) {
@@ -747,14 +751,13 @@
 +    public void broadcastAll(Packet packet, Level world) {
 +        for (int i = 0; i < world.players().size(); ++i) {
 +            ((ServerPlayer) world.players().get(i)).connection.send(packet);
-+        }
+         }
-+
+ 
-+    }
+     }
 +    // CraftBukkit end
-+
+ 
      public void broadcastAll(Packet<?> packet, ResourceKey<Level> dimension) {
          Iterator iterator = this.players.iterator();
- 
 @@ -554,7 +868,7 @@
  
      }
@@ -822,7 +825,20 @@
              if (entityplayer != player && entityplayer.level().dimension() == worldKey) {
                  double d4 = x - entityplayer.getX();
                  double d5 = y - entityplayer.getY();
-@@ -712,15 +1023,19 @@
+@@ -687,10 +998,12 @@
+     }
+ 
+     public void saveAll() {
++        io.papermc.paper.util.MCUtil.ensureMain("Save Players" , () -> { // Paper - Ensure main
+         for (int i = 0; i < this.players.size(); ++i) {
+             this.save((ServerPlayer) this.players.get(i));
+         }
+ 
++        return null; }); // Paper - ensure main
+     }
+ 
+     public UserWhiteList getWhiteList() {
+@@ -712,15 +1025,19 @@
      public void reloadWhiteList() {}
  
      public void sendLevelInfo(ServerPlayer player, ServerLevel world) {
@@ -846,7 +862,7 @@
          }
  
          player.connection.send(new ClientboundGameEventPacket(ClientboundGameEventPacket.LEVEL_CHUNKS_LOAD_START, 0.0F));
-@@ -729,8 +1044,16 @@
+@@ -729,8 +1046,16 @@
  
      public void sendAllPlayerInfo(ServerPlayer player) {
          player.inventoryMenu.sendAllDataToRemote();
@@ -864,7 +880,7 @@
      }
  
      public int getPlayerCount() {
-@@ -786,12 +1109,29 @@
+@@ -786,12 +1111,29 @@
      }
  
      public void removeAll() {
@@ -896,7 +912,7 @@
      public void broadcastSystemMessage(Component message, boolean overlay) {
          this.broadcastSystemMessage(message, (entityplayer) -> {
              return message;
-@@ -819,24 +1159,43 @@
+@@ -819,24 +1161,43 @@
      }
  
      public void broadcastChatMessage(PlayerChatMessage message, ServerPlayer sender, ChatType.Bound params) {
@@ -943,7 +959,7 @@
          }
  
          if (flag1 && sender != null) {
-@@ -845,20 +1204,27 @@
+@@ -845,20 +1206,27 @@
  
      }
  
@@ -976,7 +992,7 @@
                  Path path = file2.toPath();
  
                  if (FileUtil.isPathNormalized(path) && FileUtil.isPathPortable(path) && path.startsWith(file.getPath()) && file2.isFile()) {
-@@ -867,7 +1233,7 @@
+@@ -867,7 +1235,7 @@
              }
  
              serverstatisticmanager = new ServerStatsCounter(this.server, file1);
@@ -985,7 +1001,7 @@
          }
  
          return serverstatisticmanager;
-@@ -875,13 +1241,13 @@
+@@ -875,13 +1243,13 @@
  
      public PlayerAdvancements getPlayerAdvancements(ServerPlayer player) {
          UUID uuid = player.getUUID();
@@ -1001,7 +1017,7 @@
          }
  
          advancementdataplayer.setPlayer(player);
-@@ -932,15 +1298,28 @@
+@@ -932,15 +1300,28 @@
      }
  
      public void reloadResources() {