From 1974b3e692a1d817d837bd34a02d6e2971ada5a1 Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Sun, 12 Jun 2016 12:04:03 +0200
Subject: [PATCH] Fix deadlock waiting for Python task to end at end of program

---
 panda/src/display/graphicsEngine.cxx | 3 +++
 panda/src/display/graphicsEngine.h   | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/panda/src/display/graphicsEngine.cxx b/panda/src/display/graphicsEngine.cxx
index 9bd325fc95..da90172088 100644
--- a/panda/src/display/graphicsEngine.cxx
+++ b/panda/src/display/graphicsEngine.cxx
@@ -638,6 +638,9 @@ remove_all_windows() {
   // And, hey, let's stop the vertex paging threads, if any.
   VertexDataPage::stop_threads();
 
+  // Stopping the tasks means we have to release the Python GIL while
+  // this method runs (hence it is marked BLOCKING), so that any
+  // Python tasks on other threads won't deadlock grabbing the GIL.
   AsyncTaskManager::get_global_ptr()->stop_threads();
 
 #ifdef DO_PSTATS
diff --git a/panda/src/display/graphicsEngine.h b/panda/src/display/graphicsEngine.h
index cb371076ee..122d8be359 100644
--- a/panda/src/display/graphicsEngine.h
+++ b/panda/src/display/graphicsEngine.h
@@ -58,7 +58,7 @@ class Texture;
 class EXPCL_PANDA_DISPLAY GraphicsEngine : public ReferenceCount {
 PUBLISHED:
   GraphicsEngine(Pipeline *pipeline = NULL);
-  ~GraphicsEngine();
+  BLOCKING ~GraphicsEngine();
 
   void set_threading_model(const GraphicsThreadingModel &threading_model);
   GraphicsThreadingModel get_threading_model() const;
@@ -94,7 +94,7 @@ PUBLISHED:
 
   bool add_window(GraphicsOutput *window, int sort);
   bool remove_window(GraphicsOutput *window);
-  void remove_all_windows();
+  BLOCKING void remove_all_windows();
   void reset_all_windows(bool swapchain);
 
   bool is_empty() const;