Fix race condition when concurrently Stealing

src/main/java/server/life/Monster.java

@@ -60,6 +60,7 @@ import java.util.List;
 import java.util.*;
 import java.util.Map.Entry;
 import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.locks.Lock;
@@ -86,7 +87,7 @@ public class Monster extends AbstractLoadedLife {
     private final Set<Integer> usedAttacks = new HashSet<>();
     private Set<Integer> calledMobOids = null;
     private WeakReference<Monster> callerMob = new WeakReference<>(null);
-    private final List<Integer> stolenItems = new ArrayList<>(5);
+    private final AtomicBoolean isStolen = new AtomicBoolean(false);
     private int team;
     private int parentMobOid = 0;
     private int spawnEffect = 0;
@@ -1644,12 +1645,9 @@ public class Monster extends AbstractLoadedLife {
         return stats.getName();
     }
 
-    public void addStolen(int itemId) {
-        stolenItems.add(itemId);
-    }
-
-    public List<Integer> getStolen() {
-        return stolenItems;
+    public boolean trySteal() {
+        boolean wasAlreadyStolen = this.isStolen.getAndSet(true);
+        return !wasAlreadyStolen;
     }
 
     public void setTempEffectiveness(Element e, ElementalEffectiveness ee, long milli) {
@@ -2177,4 +2175,4 @@ public class Monster extends AbstractLoadedLife {
 
         this.getMap().dismissRemoveAfter(this);
     }
-}
+}