From 8374e23014f2254c7de23cf6f0e09e7dabd5303f Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Sat, 5 Aug 2017 00:54:34 +0200
Subject: Add API to set thread-priority (for ctrl-surfaces)

---
 libs/pbd/base_ui.cc    | 32 ++++++++++++++++++++++++++++++++
 libs/pbd/pbd/base_ui.h |  2 ++
 2 files changed, 34 insertions(+)

diff --git a/libs/pbd/base_ui.cc b/libs/pbd/base_ui.cc
index f22d83264e..b04b755ec8 100644
--- a/libs/pbd/base_ui.cc
+++ b/libs/pbd/base_ui.cc
@@ -28,6 +28,9 @@
 #include <cerrno>
 #include <cstring>
 
+#include <pthread.h>
+#include <sched.h>
+
 #include "pbd/base_ui.h"
 #include "pbd/debug.h"
 #include "pbd/pthread_utils.h"
@@ -76,6 +79,35 @@ BaseUI::new_request_type ()
 	return rt;
 }
 
+int
+BaseUI::set_thread_priority (const int policy, int priority) const
+{
+	struct sched_param param;
+	memset (&param, 0, sizeof (param));
+
+	/* POSIX requires a spread of at least 32 steps between min..max */
+	const int p_min = sched_get_priority_min (policy); // Linux: 1
+	const int p_max = sched_get_priority_max (policy); // Linux: 99
+
+	if (priority == 0) {
+		/* use default. XXX this should be relative to audio (JACK) thread,
+		 * internal backends use -20 (Audio), -21 (MIDI), -22 (compuation)
+		 */
+		priority = 7;
+	}
+
+	if (priority > 0) {
+		priority += p_min;
+	} else {
+		priority += p_max;
+	}
+	if (priority > p_max) priority = p_max;
+	if (priority < p_min) priority = p_min;
+	param.sched_priority = priority;
+
+	return pthread_setschedparam (pthread_self(), SCHED_FIFO, &param);
+}
+
 void
 BaseUI::main_thread ()
 {
diff --git a/libs/pbd/pbd/base_ui.h b/libs/pbd/pbd/base_ui.h
index 029d8223ea..b8569718ae 100644
--- a/libs/pbd/pbd/base_ui.h
+++ b/libs/pbd/pbd/base_ui.h
@@ -91,6 +91,8 @@ class LIBPBD_API BaseUI : public sigc::trackable, public PBD::EventLoop
 
 	virtual void thread_init () {};
 
+	int set_thread_priority (const int policy = SCHED_FIFO, int priority = 0) const;
+
 	/** Called when there input ready on the request_channel
 	 */
 	bool request_handler (Glib::IOCondition);
-- 
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