avoid ConcurrentModificationException by using ConcurrentHashSet

src/main/java/TdbArchiver/TdbArchiver.java

@@ -390,10 +390,11 @@ import java.sql.Timestamp;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executors;
 
 import org.omg.CORBA.SystemException;
@@ -575,8 +576,8 @@ public class TdbArchiver extends DeviceImpl implements TangoConst {
     public static final short SUCCEEDED = 20;
     public static final short FAILED = 30;
 
-    private final Set<String> koAttributes = new HashSet<String>();
-    private final Set<String> okAttributes = new HashSet<String>();
+    private final Set<String> koAttributes = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
+    private final Set<String> okAttributes = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
     private String dbSchema;
     private Logger logger;