UpdateGlue: let the update thread run at "idle" priority

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 \

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

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()) {

src/thread/Util.hxx

+/*
+ * 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