combine short periodic timeout functions for windows.

Fixes excessive CPU usage (spinlock instead of sleep/WaitForSingleObject)

MS Windows has a scheduler time-slice of 15ms.
Ardour has two fast timeout functions: The FPS timeout (20-60Hz, clock
video-monitor) and a fast-screen-update (25Hz, meters etc).
They are loosely coupled (async) and scheduled from the main application
thread (gtk main).

Since they're async, gtk schedules them as needed. Even though the actual
period of the separate timeouts is larger. The effective period between
all timeout callbacks is <15ms and the main application thread never idles.

1 files changed, 15 insertions, 0 deletions

diff --git a/gtk2_ardour/ardour_ui.cc b/gtk2_ardour/ardour_ui.cc
index 133e991a06..aeac8a1637 100644
--- a/gtk2_ardour/ardour_ui.cc
+++ b/gtk2_ardour/ardour_ui.cc
@@ -1006,7 +1006,9 @@ If you still wish to quit, please use the\n\n\
 
 		second_connection.disconnect ();
 		point_one_second_connection.disconnect ();
+#ifndef PLATFORM_WINDOWS
 		point_zero_something_second_connection.disconnect();
+#endif
 		fps_connection.disconnect();
 	}
 
@@ -1159,6 +1161,9 @@ gint
 ARDOUR_UI::every_fps ()
 {
 	FPSUpdate(); /* EMIT_SIGNAL */
+#ifdef PLATFORM_WINDOWS
+	every_point_zero_something_seconds();
+#endif
 	return TRUE;
 }
 
@@ -1178,7 +1183,17 @@ ARDOUR_UI::set_fps_timeout_connection ()
 				* _session->frame_rate() / _session->nominal_frame_rate()
 				/ _session->timecode_frames_per_second()
 				);
+#ifdef PLATFORM_WINDOWS
+		// the smallest windows scheduler time-slice is ~15ms.
+		// periodic GUI timeouts shorter than that will cause
+		// WaitForSingleObject to spinlock (100% of one CPU Core)
+		// and gtk never enters idle mode.
+		// also changing timeBeginPeriod(1) does not affect that in
+		// any beneficial way, so we just limit the max rate for now.
+		interval = std::max(30u, interval); // at most ~33Hz.
+#else
 		interval = std::max(8u, interval); // at most 120Hz.
+#endif
 	}
 	fps_connection.disconnect();
 	fps_connection = Glib::signal_timeout().connect (sigc::mem_fun(*this, &ARDOUR_UI::every_fps), interval);