video/widget: fix mutex starvation

Get rid of contention in `preview_size' and `set_image'.

After switching the Qt mutex to non-recursive, turns out the writer
thread preempts the UI thread to the point of freezing the entire thing.
Mutex fairness is an implementation detail and we must assume unfair
mutexes in the worst case.

1 files changed, 1 insertions, 2 deletions

diff --git a/tracker-pt/ftnoir_tracker_pt.cpp b/tracker-pt/ftnoir_tracker_pt.cpp
index a1a0dc1c..a2272d1c 100644
--- a/tracker-pt/ftnoir_tracker_pt.cpp
+++ b/tracker-pt/ftnoir_tracker_pt.cpp
@@ -101,8 +101,7 @@ void Tracker_PT::run()
             widget->update_image(preview_frame->get_bitmap());
 
             {
-                int w = -1, h = -1;
-                widget->get_preview_size(w, h);
+                auto [ w, h ] = widget->preview_size();
                 if (w != preview_width || h != preview_height)
                 {
                     preview_width = w; preview_height = h;