From 11d0e36b2afdaf24eb1aeeed3f319f31efc88fbd Mon Sep 17 00:00:00 2001
From: David Foster <david@dafoster.net>
Date: Tue, 26 Sep 2023 22:17:41 -0400
Subject: [PATCH] MainWindow: Mark inconsistent and non-deterministic aspects
 of closing process

---
 src/crystal/browser/__init__.py | 9 ++++++++-
 src/crystal/model.py            | 6 +++++-
 src/crystal/task.py             | 9 +++++----
 src/crystal/util/xthreading.py  | 4 +---
 4 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/crystal/browser/__init__.py b/src/crystal/browser/__init__.py
index 75542fb5..4c572a86 100644
--- a/src/crystal/browser/__init__.py
+++ b/src/crystal/browser/__init__.py
@@ -376,9 +376,16 @@ def __exit__(self, exc_type, exc_value, exc_traceback) -> None:
     # === File Menu: Events ===
     
     def _on_close_project(self, event: wx.CommandEvent) -> None:
+        # TODO: Move these dispose operations inside _on_close_frame().
+        #       But be careful! The last time this movement was attempted,
+        #       various shutdown-related race conditions were triggered.
+        #       
+        #       Wait to perform movement until enough time to formalize
+        #       a deterministic shutdown procedure.
         self.entity_tree.dispose()
         self.task_tree.dispose()
-        self._frame.Close()
+        
+        self._frame.Close()  # will trigger call to _on_close_frame()
     
     def _on_quit(self, event: wx.CommandEvent) -> None:
         if event.Id == wx.ID_EXIT:
diff --git a/src/crystal/model.py b/src/crystal/model.py
index 5127b42e..35d2153d 100644
--- a/src/crystal/model.py
+++ b/src/crystal/model.py
@@ -697,7 +697,11 @@ def _resource_group_did_instantiate(self, group: ResourceGroup) -> None:
     # === Close ===
     
     def close(self) -> None:
-        self.root_task.close()
+        # Stop scheduler thread soon
+        self.root_task.interrupt()
+        # (TODO: Actually wait for the scheduler thread to exit
+        #        in a deterministic fashion, rather than relying on 
+        #        garbage collection to clean up objects.)
         
         # Disable Write Ahead Log (WAL) mode when closing database
         # in case the user decides to burn the project to read-only media,
diff --git a/src/crystal/task.py b/src/crystal/task.py
index fad07906..bd83ddff 100644
--- a/src/crystal/task.py
+++ b/src/crystal/task.py
@@ -1299,8 +1299,6 @@ class RootTask(Task):
     
     Access to this task's children list must be synchronized with the
     foreground thread.
-    
-    This task never completes.
     """
     icon_name = None
     scheduling_style = SCHEDULING_STYLE_ROUND_ROBIN
@@ -1365,8 +1363,11 @@ def fg_task() -> None:
         # NOTE: Must synchronize access to RootTask.children with foreground thread
         fg_call_and_wait(fg_task)
     
-    def close(self) -> None:
-        """Stop all descendent tasks, asynchronously."""
+    def interrupt(self) -> None:
+        """
+        Stop all descendent tasks, asynchronously,
+        by interrupting the scheduler thread.
+        """
         self.finish()
     
     def __repr__(self) -> str:
diff --git a/src/crystal/util/xthreading.py b/src/crystal/util/xthreading.py
index 228ca309..f35c541e 100644
--- a/src/crystal/util/xthreading.py
+++ b/src/crystal/util/xthreading.py
@@ -232,9 +232,7 @@ def bg_call_later(callable: Callable[..., None], daemon: bool=False, *args) -> N
         if True, forces the background thread to be a daemon,
         and not prevent program termination while it is running.
     """
-    thread = threading.Thread(target=callable, args=args)
-    if daemon:
-        thread.daemon = True
+    thread = threading.Thread(target=callable, args=args, daemon=daemon)
     thread.start()