Properly terminate MultiProcessing Runtime (#16623)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: justusschock

src/lightning/app/CHANGELOG.md

@@ -44,6 +44,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
+- Fixed a deadlock causing apps not to exit properly when running locally ([#16623](https://github.com/Lightning-AI/lightning/pull/16623)))
+
+
 - Fixed the Drive root_folder not parsed properly ([#16454](https://github.com/Lightning-AI/lightning/pull/16454))
 
 - Fixed malformed path when downloading files using `lightning cp` ([#16626](https://github.com/Lightning-AI/lightning/pull/16626))

src/lightning/app/utilities/proxies.py

@@ -613,15 +613,16 @@ def _sigterm_signal_handler(self, signum, frame, call_hash: str) -> None:
             self.work._calls[call_hash]["statuses"].append(
                 make_status(WorkStageStatus.STOPPED, reason=WorkStopReasons.SIGTERM_SIGNAL_HANDLER)
             )
-            delta = Delta(DeepDiff(state, self.work.state, verbose_level=2))
-            self.delta_queue.put(ComponentDelta(id=self.work_name, delta=delta))
 
         # kill the thread as the job is going to be terminated.
-        self.copier.join(0)
         if self.state_observer:
             if self.state_observer.started:
                 self.state_observer.join(0)
             self.state_observer = None
+        delta = Delta(DeepDiff(state, deepcopy(self.work.state), verbose_level=2))
+        self.delta_queue.put(ComponentDelta(id=self.work_name, delta=delta))
+
+        self.copier.join(0)
         raise LightningSigtermStateException(0)
 
     def _proxy_setattr(self, cleanup: bool = False):