fix bug-6279 Parallel tasks would be Irregularly submitted twice (#6280)

dolphinscheduler-server/src/main/java/org/apache/dolphinscheduler/server/master/runner/WorkflowExecuteThread.java

@@ -192,6 +192,12 @@ public class WorkflowExecuteThread implements Runnable {
 
     private ConcurrentHashMap<Integer, TaskInstance> taskTimeoutCheckList;
 
+    /**
+     * start flag, true: start nodes submit completely
+     *
+     */
+    private boolean isStart = false;
+
     /**
      * constructor of WorkflowExecuteThread
      *
@@ -228,6 +234,14 @@ public class WorkflowExecuteThread implements Runnable {
         }
     }
 
+    /**
+     * the process start nodes are submitted completely.
+     * @return
+     */
+    public boolean isStart() {
+        return this.isStart;
+    }
+
     private void handleEvents() {
         while (this.stateEvents.size() > 0) {
 
@@ -460,10 +474,12 @@ public class WorkflowExecuteThread implements Runnable {
     }
 
     private void startProcess() throws Exception {
-        buildFlowDag();
         if (this.taskInstanceHashMap.size() == 0) {
+            isStart = false;
+            buildFlowDag();
             initTaskQueue();
             submitPostNode(null);
+            isStart = true;
         }
     }