From 5d17731b73bf485f8536fb6284ab32cdbb4789b0 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Tue, 14 Jan 2014 09:09:52 +0100
Subject: [PATCH] UpdateGlue: let the update thread run at "idle" priority

The update thread should not affect the rest of the system, therefore
set "idle" priority, and let it only run when nobody else is using the
resources.
---
 Makefile.am         |  1 +
 NEWS                |  1 +
 src/UpdateGlue.cxx  |  3 ++
 src/thread/Util.hxx | 72 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+)
 create mode 100644 src/thread/Util.hxx

diff --git a/Makefile.am b/Makefile.am
index c367ca455..e0fcde553 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -285,6 +285,7 @@ libutil_a_SOURCES = \
 # Multi-threading library
 
 libthread_a_SOURCES = \
+	src/thread/Util.hxx \
 	src/thread/Mutex.hxx \
 	src/thread/PosixMutex.hxx \
 	src/thread/CriticalSection.hxx \
diff --git a/NEWS b/NEWS
index a3be05562..3134095e3 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,7 @@ ver 0.19 (not yet released)
 * encoder:
   - shine: new encoder plugin
 * new resampler option using libsoxr
+* the update thread runs at "idle" priority
 
 ver 0.18.7 (2013/01/13)
 * playlist
diff --git a/src/UpdateGlue.cxx b/src/UpdateGlue.cxx
index 72938018a..29e5f3ca7 100644
--- a/src/UpdateGlue.cxx
+++ b/src/UpdateGlue.cxx
@@ -34,6 +34,7 @@
 #include "system/FatalError.hxx"
 #include "thread/Id.hxx"
 #include "thread/Thread.hxx"
+#include "thread/Util.hxx"
 
 #include <assert.h>
 
@@ -68,6 +69,8 @@ update_task(gcc_unused void *ctx)
 	else
 		LogDebug(update_domain, "starting");
 
+	SetThreadIdlePriority();
+
 	modified = update_walk(next.path_utf8.c_str(), next.discard);
 
 	if (modified || !db_exists()) {
diff --git a/src/thread/Util.hxx b/src/thread/Util.hxx
new file mode 100644
index 000000000..fe36468c3
--- /dev/null
+++ b/src/thread/Util.hxx
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_THREAD_UTIL_HXX
+#define MPD_THREAD_UTIL_HXX
+
+#ifdef __linux__
+#include <sched.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#elif defined(WIN32)
+#include <windows.h>
+#endif
+
+#ifdef __linux__
+
+static int
+ioprio_set(int which, int who, int ioprio)
+{
+	return syscall(SYS_ioprio_set, which, who, ioprio);
+}
+
+static void
+ioprio_set_idle()
+{
+	static constexpr int _IOPRIO_WHO_PROCESS = 1;
+	static constexpr int _IOPRIO_CLASS_IDLE = 3;
+	static constexpr int _IOPRIO_CLASS_SHIFT = 13;
+	static constexpr int _IOPRIO_IDLE =
+		(_IOPRIO_CLASS_IDLE << _IOPRIO_CLASS_SHIFT) | 7;
+
+	ioprio_set(_IOPRIO_WHO_PROCESS, 0, _IOPRIO_IDLE);
+}
+
+#endif
+
+/**
+ * Lower the current thread's priority to "idle" (very low).
+ */
+static inline void
+SetThreadIdlePriority()
+{
+#ifdef __linux__
+#ifdef SCHED_IDLE
+	static struct sched_param sched_param;
+	sched_setscheduler(0, SCHED_IDLE, &sched_param);
+#endif
+
+	ioprio_set_idle();
+
+#elif defined(WIN32)
+	SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_IDLE);
+#endif
+};
+
+#endif