Index: src/core/org/apache/jmeter/engine/StandardJMeterEngine.java
===================================================================
--- src/core/org/apache/jmeter/engine/StandardJMeterEngine.java	(revision 1174430)
+++ src/core/org/apache/jmeter/engine/StandardJMeterEngine.java	(working copy)
@@ -570,9 +570,11 @@
      * </ul> 
      */
     private void stopAllThreads() {
-        // ConcurrentHashMap does not need synch. here
-        for (JMeterThread item : allThreads.keySet()) {
-            item.stop();
+        for (Iterator<Map.Entry<JMeterThread, Thread>> iterator = allThreads.entrySet().iterator(); iterator.hasNext();) {
+            Map.Entry<JMeterThread, Thread> entry = iterator.next();
+            entry.getKey().stop();
+            // 51880
+            entry.getValue().interrupt();
         }
     }