Maintain strong reference for online users (#6247)

Possibly fixes #6241

Author: JRoy

Essentials/src/main/java/com/earth2me/essentials/EssentialsPlayerListener.java

@@ -6,6 +6,7 @@
 import com.earth2me.essentials.textreader.KeywordReplacer;
 import com.earth2me.essentials.textreader.TextInput;
 import com.earth2me.essentials.textreader.TextPager;
+import com.earth2me.essentials.userstorage.ModernUserMap;
 import com.earth2me.essentials.utils.AdventureUtil;
 import com.earth2me.essentials.utils.CommonPlaceholders;
 import com.earth2me.essentials.utils.DateUtil;
@@ -346,6 +347,7 @@ public void delayedJoin(final Player player, final String message) {
 
         ess.getBackup().onPlayerJoin();
         final User dUser = ess.getUser(player);
+        ((ModernUserMap) ess.getUsers()).getOnlineUserCache().put(player.getUniqueId(), dUser);
         dUser.update(player);
 
         dUser.startTransaction();

Essentials/src/main/java/com/earth2me/essentials/UserData.java

@@ -74,6 +74,7 @@ public final void reset() {
 
     public final void cleanup() {
         config.blockingSave();
+        ess.getUsers().invalidate(getConfigUUID());
     }
 
     @Override

Essentials/src/main/java/com/earth2me/essentials/userstorage/ModernUserMap.java

@@ -24,6 +24,7 @@ public class ModernUserMap extends CacheLoader<UUID, User> implements IUserMap {
     private final transient IEssentials ess;
     private final transient ModernUUIDCache uuidCache;
     private final transient LoadingCache<UUID, User> userCache;
+    private final transient ConcurrentMap<UUID, User> onlineUserCache;
 
     private final boolean debugPrintStackWithWarn;
     private final long debugMaxWarnsPerType;
@@ -50,6 +51,7 @@ public ModernUserMap(final IEssentials ess) {
         this.debugPrintStackWithWarn = Boolean.parseBoolean(printStackProperty);
         this.debugLogCache = Boolean.parseBoolean(logCacheProperty);
         this.debugNonPlayerWarnCounts = new ConcurrentHashMap<>();
+        this.onlineUserCache = new ConcurrentHashMap<>();
     }
 
     @Override
@@ -91,6 +93,10 @@ public User getUser(final Player base) {
         return user;
     }
 
+    public ConcurrentMap<UUID, User> getOnlineUserCache() {
+        return onlineUserCache;
+    }
+
     @Override
     public User getUser(final String name) {
         if (name == null) {
@@ -207,6 +213,7 @@ public void blockingSave() {
     public void invalidate(final UUID uuid) {
         userCache.invalidate(uuid);
         uuidCache.removeCache(uuid);
+        onlineUserCache.remove(uuid);
     }
 
     private File getUserFile(final UUID uuid) {
@@ -215,6 +222,7 @@ private File getUserFile(final UUID uuid) {
 
     public void shutdown() {
         uuidCache.shutdown();
+        onlineUserCache.clear();
     }
 
     private void debugLogCache(final User user) {