From 6e82f3669f644d0e73fa29c033ebe85f4c77dffc Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Thu, 10 Jun 2021 03:17:13 +0200
Subject: [PATCH] Correctly set ctrl-surface thread priority

---
 libs/ardour/session.cc | 3 +++
 libs/pbd/base_ui.cc    | 6 ++++--
 libs/pbd/pbd/base_ui.h | 7 ++++++-
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 60d4583c73..5c8f6c1d8d 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -47,6 +47,7 @@
 #include <boost/algorithm/string/erase.hpp>
 
 #include "pbd/basename.h"
+#include "pbd/base_ui.h"
 #include "pbd/convert.h"
 #include "pbd/error.h"
 #include "pbd/file_utils.h"
@@ -542,6 +543,8 @@ Session::immediately_post_engine ()
 		_process_graph.reset (new Graph (*this));
 	}
 
+	BaseUI::set_thread_priority (pbd_absolute_rt_priority (PBD_SCHED_FIFO, AudioEngine::instance()->client_real_time_priority () - 3));
+
 	/* every time we reconnect, recompute worst case output latencies */
 
 	_engine.Running.connect_same_thread (*this, boost::bind (&Session::initialize_latencies, this));
diff --git a/libs/pbd/base_ui.cc b/libs/pbd/base_ui.cc
index 2ea27a0652..32a0b9557d 100644
--- a/libs/pbd/base_ui.cc
+++ b/libs/pbd/base_ui.cc
@@ -50,6 +50,8 @@ using namespace PBD;
 using namespace Glib;
 
 uint64_t BaseUI::rt_bit = 1;
+int BaseUI::_thread_priority = PBD_RT_PRI_PROC - 1;
+
 BaseUI::RequestType BaseUI::CallSlot = BaseUI::new_request_type();
 BaseUI::RequestType BaseUI::Quit = BaseUI::new_request_type();
 
@@ -83,9 +85,9 @@ BaseUI::new_request_type ()
 }
 
 int
-BaseUI::set_thread_priority (const int policy, int priority) const
+BaseUI::set_thread_priority () const
 {
-	return pbd_set_thread_priority (pthread_self(), policy, priority);
+	return pbd_set_thread_priority (pthread_self(), PBD_SCHED_FIFO, _thread_priority);
 }
 
 void
diff --git a/libs/pbd/pbd/base_ui.h b/libs/pbd/pbd/base_ui.h
index 37209637b8..af501fc666 100644
--- a/libs/pbd/pbd/base_ui.h
+++ b/libs/pbd/pbd/base_ui.h
@@ -62,6 +62,10 @@ class LIBPBD_API BaseUI : public sigc::trackable, public PBD::EventLoop
 	static RequestType CallSlot;
 	static RequestType Quit;
 
+	static void set_thread_priority (int p) {
+		_thread_priority = p;
+	}
+
 	/** start up a thread to run the main loop
 	 */
 	void run ();
@@ -93,7 +97,7 @@ class LIBPBD_API BaseUI : public sigc::trackable, public PBD::EventLoop
 
 	virtual void thread_init () {};
 
-	int set_thread_priority (const int policy = PBD_SCHED_FIFO, int priority = 0) const;
+	int set_thread_priority () const;
 
 	/** Called when there input ready on the request_channel
 	 */
@@ -114,6 +118,7 @@ class LIBPBD_API BaseUI : public sigc::trackable, public PBD::EventLoop
 	CrossThreadChannel request_channel;
 
 	static uint64_t rt_bit;
+	static int _thread_priority;
 
 	int setup_request_pipe ();
 	void main_thread ();