diff --git a/lib/tmengine.jar b/lib/tmengine.jar
index ece564b..3c97b83 100644
Binary files a/lib/tmengine.jar and b/lib/tmengine.jar differ
diff --git a/src/com/maxprograms/tmengine/Constants.java b/src/com/maxprograms/tmengine/Constants.java
index b671d80..e9c788f 100644
--- a/src/com/maxprograms/tmengine/Constants.java
+++ b/src/com/maxprograms/tmengine/Constants.java
@@ -18,8 +18,8 @@ private Constants() {
 	}
 
 	public static final String CREATIONTOOL = "Maxprograms TM Engine";
-	public static final String VERSION = "5.0.1";
-	public static final String BUILD = "20191212_0727";
+	public static final String VERSION = "5.0.2";
+	public static final String BUILD = "20201123_0623";
 
 	public static final String PENDING = "Pending";
 	public static final String COMPLETED = "Completed";
diff --git a/src/com/maxprograms/tmengine/MapDbEngine.java b/src/com/maxprograms/tmengine/MapDbEngine.java
index ae0032d..3874e13 100644
--- a/src/com/maxprograms/tmengine/MapDbEngine.java
+++ b/src/com/maxprograms/tmengine/MapDbEngine.java
@@ -18,9 +18,8 @@
 import java.lang.System.Logger.Level;
 import java.nio.charset.StandardCharsets;
 import java.text.MessageFormat;
-import java.util.ArrayList;
 import java.util.Calendar;
-import java.util.HashMap;
+import java.util.Collections;
 import java.util.Hashtable;
 import java.util.Iterator;
 import java.util.List;
@@ -28,6 +27,7 @@
 import java.util.NavigableSet;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.Vector;
 import java.util.regex.Pattern;
 import java.util.regex.PatternSyntaxException;
 
@@ -64,7 +64,7 @@ public class MapDbEngine implements ITmEngine, AutoCloseable {
 
 	public MapDbEngine(String dbname, String workFolder) throws IOException {
 		this.dbname = dbname;
-		tuAttributes = new TreeSet<>();
+		tuAttributes = Collections.synchronizedSortedSet(new TreeSet<>());
 		String[] array = new String[] { "tuid", "o-encoding", "datatype", "usagecount", "lastusagedate", "creationtool",
 				"creationtoolversion", "creationdate", "creationid", "changedate", "segtype", "changeid", "o-tmf",
 				"srclang" };
@@ -111,7 +111,7 @@ public String getType() {
 	}
 
 	@Override
-	public void close() throws IOException {
+	public synchronized void close() throws IOException {
 		fuzzyIndex.close();
 		tuDb.close();
 		tuvDb.close();
@@ -203,7 +203,7 @@ public Set<String> getAllSubjects() {
 	public List<Match> searchTranslation(String searchStr, String srcLang, String tgtLang, int similarity,
 			boolean caseSensitive) throws IOException, SAXException, ParserConfigurationException {
 
-		List<Match> result = new ArrayList<>();
+		List<Match> result = new Vector<>();
 
 		if (similarity == 100) {
 			// check for perfect matches
@@ -241,7 +241,7 @@ public List<Match> searchTranslation(String searchStr, String srcLang, String tg
 			int min = size * similarity / 100;
 			int max = size * (200 - similarity) / 100;
 
-			Map<String, Integer> candidates = new HashMap<>();
+			Map<String, Integer> candidates = new Hashtable<>();
 			String lowerSearch = searchStr.toLowerCase();
 
 			NavigableSet<Fun.Tuple2<Integer, String>> index = fuzzyIndex.getIndex(srcLang);
@@ -322,7 +322,7 @@ private Element buildElement(Map<String, String> properties)
 	@Override
 	public List<Element> concordanceSearch(String searchStr, String srcLang, int limit, boolean isRegexp,
 			boolean caseSensitive) throws IOException, SAXException, ParserConfigurationException {
-		List<Element> result = new ArrayList<>();
+		List<Element> result = new Vector<>();
 		Pattern pattern = null;
 		if (isRegexp) {
 			try {
@@ -379,7 +379,7 @@ public void storeTu(Element tu) throws IOException {
 		if (tu.getAttributeValue("creationid").isEmpty()) {
 			tu.setAttribute("creationid", System.getProperty("user.name"));
 		}
-		Map<String, String> tuProperties = new HashMap<>();
+		Map<String, String> tuProperties = new Hashtable<>();
 
 		List<Attribute> atts = tu.getAttributes();
 		Iterator<Attribute> at = atts.iterator();
@@ -403,7 +403,7 @@ public void storeTu(Element tu) throws IOException {
 			tuProperties.put("project", currProject);
 		}
 		List<Element> tuvs = tu.getChildren("tuv");
-		Set<String> tuLangs = new TreeSet<>();
+		Set<String> tuLangs = Collections.synchronizedSortedSet(new TreeSet<>());
 
 		Iterator<Element> it = tuvs.iterator();
 		while (it.hasNext()) {
@@ -440,7 +440,7 @@ public void storeTu(Element tu) throws IOException {
 	}
 
 	@Override
-	public void commit() {
+	public synchronized void commit() {
 		fuzzyIndex.commit();
 		tuDb.commit();
 		tuvDb.commit();
diff --git a/src/com/maxprograms/tmengine/NGrams.java b/src/com/maxprograms/tmengine/NGrams.java
index 3a0ceac..c1ed458 100644
--- a/src/com/maxprograms/tmengine/NGrams.java
+++ b/src/com/maxprograms/tmengine/NGrams.java
@@ -11,12 +11,13 @@
  *******************************************************************************/
 package com.maxprograms.tmengine;
 
-import java.util.ArrayList;
-import java.util.HashSet;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.StringTokenizer;
+import java.util.TreeSet;
+import java.util.Vector;
 
 public class NGrams {
 
@@ -32,7 +33,7 @@ private NGrams() {
 	public static int[] getNGrams(String string) {
 		String src = string.toLowerCase();
 		List<String> words = buildWordList(src);
-		Set<String> set = new HashSet<>();
+		Set<String> set = Collections.synchronizedSortedSet(new TreeSet<>());
 		
 		Iterator<String> it = words.iterator();
 		while (it.hasNext()) {
@@ -64,7 +65,7 @@ public static int[] getNGrams(String string) {
 	}
 
 	private static List<String> buildWordList(String src) {
-		List<String> result = new ArrayList<>();
+		List<String> result = new Vector<>();
 		StringTokenizer tokenizer = new StringTokenizer(src, SEPARATORS);
 		while (tokenizer.hasMoreElements()) {
 			result.add(tokenizer.nextToken());
diff --git a/src/com/maxprograms/tmengine/SQLEngine.java b/src/com/maxprograms/tmengine/SQLEngine.java
index 4fb5e17..4322c07 100644
--- a/src/com/maxprograms/tmengine/SQLEngine.java
+++ b/src/com/maxprograms/tmengine/SQLEngine.java
@@ -23,8 +23,8 @@
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
-import java.util.ArrayList;
 import java.util.Calendar;
+import java.util.Collections;
 import java.util.Hashtable;
 import java.util.Iterator;
 import java.util.List;
@@ -32,17 +32,18 @@
 import java.util.Properties;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.Vector;
 
 import javax.xml.parsers.ParserConfigurationException;
 
-import org.xml.sax.SAXException;
-
-import com.maxprograms.tmx.TMXReader;
 import com.maxprograms.tmutils.TMUtils;
+import com.maxprograms.tmx.TMXReader;
 import com.maxprograms.xml.Attribute;
 import com.maxprograms.xml.Element;
 import com.maxprograms.xml.Indenter;
 
+import org.xml.sax.SAXException;
+
 public class SQLEngine implements ITmEngine {
 
 	private static final Logger LOGGER = System.getLogger(SQLEngine.class.getName());
@@ -61,7 +62,7 @@ public class SQLEngine implements ITmEngine {
 
 	private long next;
 
-	private TreeSet<String> languages;
+	private Set<String> languages;
 
 	private PreparedStatement insertProperties;
 	private PreparedStatement removeProperties;
@@ -282,7 +283,7 @@ public void flag(String tuid) throws SQLException {
 
 	@Override
 	public Set<String> getAllClients() throws SQLException {
-		Set<String> result = new TreeSet<>();
+		Set<String> result = Collections.synchronizedSortedSet(new TreeSet<>());
 		try (Statement stmt = conn.createStatement()) {
 			try (ResultSet rs = stmt
 					.executeQuery("SELECT DISTINCT content FROM `" + dbName + "`.tuprop WHERE propType='customer'")) {
@@ -297,7 +298,7 @@ public Set<String> getAllClients() throws SQLException {
 	@Override
 	public Set<String> getAllLanguages() throws SQLException {
 		if (languages == null) {
-			languages = new TreeSet<>();
+			languages = Collections.synchronizedSortedSet(new TreeSet<>());
 			try (Statement stmt = conn.createStatement()) {
 				try (ResultSet rs = stmt.executeQuery("SELECT lang FROM `" + dbName + "`.langs")) {
 					while (rs.next()) {
@@ -311,7 +312,7 @@ public Set<String> getAllLanguages() throws SQLException {
 
 	@Override
 	public Set<String> getAllProjects() throws SQLException {
-		Set<String> result = new TreeSet<>();
+		Set<String> result = Collections.synchronizedSortedSet(new TreeSet<>());
 		try (Statement stmt = conn.createStatement()) {
 			try (ResultSet rs = stmt
 					.executeQuery("SELECT DISTINCT content FROM `" + dbName + "`.tuprop WHERE propType='project'")) {
@@ -325,7 +326,7 @@ public Set<String> getAllProjects() throws SQLException {
 
 	@Override
 	public Set<String> getAllSubjects() throws SQLException {
-		Set<String> result = new TreeSet<>();
+		Set<String> result = Collections.synchronizedSortedSet(new TreeSet<>());
 		try (Statement stmt = conn.createStatement()) {
 			try (ResultSet rs = stmt
 					.executeQuery("SELECT DISTINCT content FROM `" + dbName + "`.tuprop WHERE propType='subject'")) {
@@ -340,7 +341,7 @@ public Set<String> getAllSubjects() throws SQLException {
 	@Override
 	public List<Match> searchTranslation(String searchStr, String srcLang, String tgtLang, int similarity,
 			boolean caseSensitive) throws IOException, SAXException, ParserConfigurationException, SQLException {
-		List<Match> result = new ArrayList<>();
+		List<Match> result = new Vector<>();
 
 		int[] ngrams = NGrams.getNGrams(searchStr);
 		int size = ngrams.length;
@@ -357,7 +358,7 @@ public List<Match> searchTranslation(String searchStr, String srcLang, String tg
 			set.append("," + ngrams[i]);
 		}
 
-		Set<String> candidates = new TreeSet<>();
+		Set<String> candidates = Collections.synchronizedSortedSet(new TreeSet<>());
 		String lowerSearch = searchStr.toLowerCase();
 
 		PreparedStatement stmt = selectNgram.get(srcLang);
@@ -420,7 +421,7 @@ private String getPureText(String lang, String tuid) throws SQLException {
 	@Override
 	public List<Element> concordanceSearch(String searchStr, String srcLang, int limit, boolean isRegexp,
 			boolean caseSensitive) throws IOException, SAXException, ParserConfigurationException, SQLException {
-		Set<String> candidates = new TreeSet<>();
+		Set<String> candidates = Collections.synchronizedSortedSet(new TreeSet<>());
 		if (isRegexp) {
 			try (PreparedStatement stmt = conn.prepareStatement(
 					"SELECT tuid, pureText FROM `" + dbName + "`.tuv WHERE lang=? AND pureText REGEXP ? LIMIT ?")) {
@@ -460,7 +461,7 @@ public List<Element> concordanceSearch(String searchStr, String srcLang, int lim
 				}
 			}
 		}
-		List<Element> result = new ArrayList<>();
+		List<Element> result = new Vector<>();
 		Iterator<String> it = candidates.iterator();
 		while (it.hasNext()) {
 			Element tu = getTu(it.next());
@@ -511,7 +512,7 @@ public void storeTu(Element tu) throws IOException, SQLException {
 			tuProperties.put("project", currProject);
 		}
 		List<Element> tuvs = tu.getChildren("tuv");
-		Set<String> tuLangs = new TreeSet<>();
+		Set<String> tuLangs = Collections.synchronizedSortedSet(new TreeSet<>());
 
 		Iterator<Element> it = tuvs.iterator();
 		while (it.hasNext()) {
@@ -659,7 +660,7 @@ public void commit() throws SQLException {
 	private Element getTu(String tuid, Set<String> langs)
 			throws SQLException, SAXException, IOException, ParserConfigurationException {
 		if (tuAttributes == null) {
-			tuAttributes = new TreeSet<>();
+			tuAttributes = Collections.synchronizedSortedSet(new TreeSet<>());
 			String[] array = new String[] { "tuid", "o-encoding", "datatype", "usagecount", "lastusagedate",
 					"creationtool", "creationtoolversion", "creationdate", "creationid", "changedate", "segtype",
 					"changeid", "o-tmf", "srclang" };
@@ -699,7 +700,7 @@ private Element getTu(String tuid, Set<String> langs)
 
 	@Override
 	public Element getTu(String tuid) throws IOException, SAXException, ParserConfigurationException, SQLException {
-		return getTu(tuid, new TreeSet<>());
+		return getTu(tuid, Collections.synchronizedSortedSet(new TreeSet<>()));
 	}
 
 	private String getSegText(String lang, String tuid) throws SQLException {
diff --git a/src/com/maxprograms/tmserver/TmHandler.java b/src/com/maxprograms/tmserver/TmHandler.java
index c682544..6a57407 100644
--- a/src/com/maxprograms/tmserver/TmHandler.java
+++ b/src/com/maxprograms/tmserver/TmHandler.java
@@ -27,9 +27,9 @@
 import java.nio.file.Files;
 import java.sql.SQLException;
 import java.text.SimpleDateFormat;
+import java.util.Collections;
 import java.util.Date;
 import java.util.Enumeration;
-import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -388,7 +388,7 @@ private JSONObject exportMemory(String request) {
                 }
                 Set<String> langs = null;
                 if (json.has("langs")) {
-                    langs = new TreeSet<>();
+                    langs = Collections.synchronizedSortedSet(new TreeSet<>());
                     JSONArray array = json.getJSONArray("langs");
                     for (int i = 0; i < array.length(); i++) {
                         langs.add(array.getString(i));
@@ -396,7 +396,7 @@ private JSONObject exportMemory(String request) {
                 }
                 Map<String, String> properties = null;
                 if (json.has("properties")) {
-                    properties = new HashMap<>();
+                    properties = new ConcurrentHashMap<>();
                     JSONObject props = json.getJSONObject("properties");
                     Iterator<String> keys = props.keys();
                     while (keys.hasNext()) {
@@ -475,9 +475,7 @@ protected void open(String id) throws IOException, SQLException {
         } else if ("SQLEngine".equals(mem.getString("type"))) {
             openEngines.put(id, new SQLEngine(mem.getString("name"), mem.getString("serverName"), mem.getInt("port"),
                     mem.getString("userName"), mem.getString("password")));
-        } else {
-            throw new IOException("Unknown memory type");
-        }
+        } 
     }
 
     protected void close(String id) throws IOException, SQLException {