[App] Fixing Sigterm Handler causing thread lock which caused Keyboar…

…dInterrupt to hang (#15881)

* terminating only once

* changelog

src/lightning_app/CHANGELOG.md

@@ -42,6 +42,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Fixed the `enable_spawn` method of the `WorkRunExecutor` ([#15812](https://github.com/Lightning-AI/lightning/pull/15812)
 
+- Fixed Sigterm Handler causing thread lock which caused KeyboardInterrupt to hang ([#15881](https://github.com/Lightning-AI/lightning/pull/15881))
+
 
 ## [1.8.3] - 2022-11-22
 

src/lightning_app/runners/multiprocess.py

@@ -27,6 +27,7 @@ class MultiProcessRuntime(Runtime):
     """
 
     backend: Union[str, Backend] = "multiprocessing"
+    _has_triggered_termination: bool = False
 
     def dispatch(self, *args: Any, on_before_run: Optional[Callable] = None, **kwargs: Any):
         """Method to dispatch and run the LightningApp."""
@@ -111,9 +112,11 @@ def dispatch(self, *args: Any, on_before_run: Optional[Callable] = None, **kwarg
             self.app._run()
         except KeyboardInterrupt:
             self.terminate()
+            self._has_triggered_termination = True
             raise
         finally:
-            self.terminate()
+            if not self._has_triggered_termination:
+                self.terminate()
 
     def terminate(self):
         if APP_SERVER_IN_CLOUD: