Fix argon and balloon blocking application shutdown

src/main/java/com/password4j/Argon2Function.java

@@ -101,7 +101,7 @@ public class Argon2Function extends AbstractHashingFunction
 
         if (parallelism >= 1)
         {
-            service = Executors.newFixedThreadPool(Utils.AVAILABLE_PROCESSORS);
+            service = Utils.createExecutorService();
         }
     }
 

src/main/java/com/password4j/BalloonHashingFunction.java

@@ -59,7 +59,7 @@ public class BalloonHashingFunction extends AbstractHashingFunction
         this.delta = delta;
         if (parallelism > 1)
         {
-            this.service = Executors.newFixedThreadPool(Utils.AVAILABLE_PROCESSORS);
+            this.service = Utils.createExecutorService();
         }
 
     }

src/main/java/com/password4j/Utils.java

@@ -32,6 +32,9 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Random;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -50,6 +53,10 @@ class Utils
 
     private static final int[] FROM_BASE64 = new int[256];
 
+    private static final AtomicInteger THREAD_COUNTER = new AtomicInteger(1);
+
+    private static final ThreadGroup THREAD_GROUP = new ThreadGroup("Password4j Workers");
+
     static
     {
         Arrays.fill(FROM_BASE64, -1);
@@ -655,6 +662,11 @@ static List<byte[]> split(byte[] array, byte delimiter) {
         return byteArrays;
     }
 
-
-
+    static ExecutorService createExecutorService() {
+        return Executors.newFixedThreadPool(AVAILABLE_PROCESSORS, runnable -> {
+            Thread thread = new Thread(THREAD_GROUP, runnable, "password4j-worker-" + THREAD_COUNTER.getAndIncrement());
+            thread.setDaemon(true);
+            return thread;
+        });
+    }
 }