Not allow shutdown while still jobs running. (NVIDIA#454)

* Not allow shutdown while still jobs running.

* Added protection for restart.

nvflare/private/fed/server/training_cmds.py

@@ -442,6 +442,10 @@ def shutdown(self, conn: Connection, args: List[str]):
         if not isinstance(engine, ServerEngineInternalSpec):
             raise TypeError("engine must be ServerEngineInternalSpec but got {}".format(type(engine)))
 
+        if engine.job_runner.running_jobs:
+            conn.append_error("There are still jobs running. Please let them finish or abort_job before shutdown.")
+            return
+
         if target_type == self.TARGET_TYPE_SERVER:
             if engine.get_clients():
                 conn.append_error("There are still active clients. Shutdown all clients first.")
@@ -516,6 +520,10 @@ def restart(self, conn: Connection, args: List[str]):
         if not isinstance(engine, ServerEngineInternalSpec):
             raise TypeError("engine must be ServerEngineInternalSpec but got {}".format(type(engine)))
 
+        if engine.job_runner.running_jobs:
+            conn.append_error("There are still jobs running. Please let them finish or abort_job before restart.")
+            return
+
         target_type = args[1]
         if target_type == self.TARGET_TYPE_SERVER or target_type == self.TARGET_TYPE_ALL: