Merge pull request #474 from maiken2051/master

Query with timer can throw IllegalThreadStateException - This PR makes sure the ThreadGroup is not destroyed before creating a new timer thread.

src/main/java/com/microsoft/sqlserver/jdbc/IOBuffer.java

@@ -64,6 +64,7 @@
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -7119,13 +7120,21 @@ final class TimeoutTimer implements Runnable {
     private volatile Future<?> task;
 
     private static final ExecutorService executor = Executors.newCachedThreadPool(new ThreadFactory() {
-        private final ThreadGroup tg = new ThreadGroup(threadGroupName);
-        private final String threadNamePrefix = tg.getName() + "-";
+        private final AtomicReference<ThreadGroup> tgr = new AtomicReference<>();
         private final AtomicInteger threadNumber = new AtomicInteger(0);
 
         @Override
-        public Thread newThread(Runnable r) {
-            Thread t = new Thread(tg, r, threadNamePrefix + threadNumber.incrementAndGet());
+        public Thread newThread(Runnable r)
+        {
+            ThreadGroup tg = tgr.get();
+
+            if (tg == null || tg.isDestroyed())
+            {
+                tg = new ThreadGroup(threadGroupName);
+                tgr.set(tg);
+            }
+
+            Thread t = new Thread(tg, r, tg.getName() + "-" + threadNumber.incrementAndGet());
             t.setDaemon(true);
             return t;
         }