Fix various potential memory leak and concurrency issues with acccount storage

api/src/main/java/net/islandearth/rpgregions/managers/data/IStorageManager.java

@@ -42,11 +42,17 @@ public interface IStorageManager {
     void clearDiscovery(UUID uuid, String regionId);
 
     void deleteAccount(UUID uuid);
+
     /**
-     * Removes an account from the storage cache and saves its data.
+     * Removes an account from the storage cache and optionally saves its data.
      * @param uuid player's UUID
+     * @param save whether to save the player's data
      */
-    CompletableFuture<Void> removeCachedAccount(UUID uuid);
+    CompletableFuture<Void> removeCachedAccount(UUID uuid, boolean save);
+
+    default CompletableFuture<Void> removeCachedAccount(UUID uuid) {
+        return removeCachedAccount(uuid, true);
+    }
 
     /**
      * Gets a UUID safe to use in databases.

rpgregions/src/main/java/net/islandearth/rpgregions/listener/ConnectionListener.java

@@ -5,8 +5,11 @@ import net.islandearth.rpgregions.managers.data.account.RPGRegionsAccount;
 import org.bukkit.ChatColor;
 import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
 import org.bukkit.event.player.AsyncPlayerPreLoginEvent;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.player.PlayerLoginEvent;
 import org.bukkit.event.player.PlayerQuitEvent;
 
 import java.util.UUID;
@@ -14,12 +17,46 @@ import java.util.UUID;
 public record ConnectionListener(RPGRegions plugin) implements Listener {
 
     @EventHandler
+    public void onJoin(PlayerJoinEvent event) {
+        final Player player = event.getPlayer();
+        if (!plugin.getManagers().getStorageManager().getCachedAccounts().containsKey(player.getUniqueId())) {
+            player.kickPlayer(ChatColor.RED + "Player user data not present! Please contact an administrator.");
+        }
+    }
+
+    // PlayerLoginEvent is called AFTER AsyncPlayerPreLoginEvent
+    // We can't really avoid loading the user first unfortunately
+    @EventHandler(priority = EventPriority.HIGHEST) // Highest so we are always the last called
+    public void onValidate(final PlayerLoginEvent event) {
+        if (event.getResult() != PlayerLoginEvent.Result.ALLOWED) {
+            // DO NOT save the user if this is due to whitelist!
+            // If they are a new user that was prevented from joining due to whitelist
+            // Then when they join after whitelist is disabled, they will not be considered new
+            // Also saves performance
+            plugin.getManagers().getStorageManager().removeCachedAccount(event.getPlayer().getUniqueId(), false);
+        }
+    }
+
+    @EventHandler(priority = EventPriority.HIGHEST) // Highest so we are always the last called
     public void onJoin(AsyncPlayerPreLoginEvent event) {
+        // If something else has prevented the player from joining, we don't want to load the user.
+        // Otherwise, we will get memory leaks.
+        if (event.getLoginResult() != AsyncPlayerPreLoginEvent.Result.ALLOWED) return;
+
         UUID uuid = event.getUniqueId();
+
+        // If the user is present then we still haven't saved, prevent them joining to avoid corrupt data
+        if (plugin.getManagers().getStorageManager().getCachedAccounts().containsKey(uuid)) {
+            event.disallow(AsyncPlayerPreLoginEvent.Result.KICK_OTHER, ChatColor.YELLOW + "You're rejoining too quickly! Give us a moment to save your data.");
+            return;
+        }
+
         try {
             RPGRegionsAccount account = plugin.getManagers().getStorageManager().getAccount(uuid).get();
             if (account != null) return;
         } catch (Exception e) {
+            // If there was an error, don't allow entry!
+            event.disallow(AsyncPlayerPreLoginEvent.Result.KICK_OTHER, ChatColor.RED + "An error occurred whilst loading player user data! Please contact an administrator.");
             e.printStackTrace();
         }
 

rpgregions/src/main/java/net/islandearth/rpgregions/managers/data/SQLCommonStorage.java

@@ -98,8 +98,13 @@ public abstract class SQLCommonStorage implements IStorageManager {
     }
 
     @Override
-    public CompletableFuture<Void> removeCachedAccount(UUID uuid) {
+    public CompletableFuture<Void> removeCachedAccount(UUID uuid, boolean save) {
         RPGRegionsAccount account = cachedAccounts.get(uuid);
+        if (!save) {
+            cachedAccounts.remove(uuid);
+            return CompletableFuture.completedFuture(null);
+        }
+
         return DB.getResultsAsync(SELECT_REGION, getDatabaseUuid(uuid)).thenAccept(results -> {
             List<String> current = new ArrayList<>();
             for (DbRow row : results) {

rpgregions/src/main/java/net/islandearth/rpgregions/managers/data/yml/YamlStorage.java

@@ -135,8 +135,9 @@ public class YamlStorage implements IStorageManager {
     }
 
     @Override
-    public CompletableFuture<Void> removeCachedAccount(UUID uuid) {
-        RPGRegionsAccount account = cachedAccounts.get(uuid);
+    public CompletableFuture<Void> removeCachedAccount(UUID uuid, boolean save) {
+        RPGRegionsAccount account = cachedAccounts.remove(uuid);
+        if (!save) return CompletableFuture.completedFuture(null);
         File file = new File(plugin.getDataFolder() + "/accounts/" + uuid.toString() + ".yml");
         FileConfiguration config = YamlConfiguration.loadConfiguration(file);
 
@@ -151,7 +152,6 @@ public class YamlStorage implements IStorageManager {
         } catch (IOException e) {
             e.printStackTrace();
         }
-        cachedAccounts.remove(uuid);
         return CompletableFuture.completedFuture(null);
     }
 }