lib/systemd/Watchdog: implement the systemd watchdog protocol

Makefile.am

@@ -205,6 +205,11 @@ libmpd_a_SOURCES += \
 	src/unix/PidFile.hxx
 endif
 
+if ENABLE_SYSTEMD_DAEMON
+libmpd_a_SOURCES += \
+	src/lib/systemd/Watchdog.cxx src/lib/systemd/Watchdog.hxx
+endif
+
 endif
 
 if ENABLE_DATABASE

NEWS

@@ -36,6 +36,7 @@ ver 0.21 (not yet released)
   - sndio: new mixer plugin
 * encoder
   - opus: support for sending metadata using ogg stream chaining
+* systemd watchdog support
 * require GCC 6
 
 ver 0.20.21 (not yet released)

src/Instance.cxx

@@ -41,6 +41,9 @@
 
 Instance::Instance()
 	:rtio_thread(true),
+#ifdef ENABLE_SYSTEMD_DAEMON
+	 systemd_watchdog(event_loop),
+#endif
 	 idle_monitor(event_loop, BIND_THIS_METHOD(OnIdle))
 {
 }

src/Instance.hxx

@@ -26,6 +26,10 @@
 #include "event/MaskMonitor.hxx"
 #include "Compiler.h"
 
+#ifdef ENABLE_SYSTEMD_DAEMON
+#include "lib/systemd/Watchdog.hxx"
+#endif
+
 #ifdef ENABLE_CURL
 #include "RemoteTagCacheHandler.hxx"
 #endif
@@ -89,6 +93,10 @@ struct Instance final
 	 */
 	EventThread rtio_thread;
 
+#ifdef ENABLE_SYSTEMD_DAEMON
+	Systemd::Watchdog systemd_watchdog;
+#endif
+
 	MaskMonitor idle_monitor;
 
 #ifdef ENABLE_NEIGHBOR_PLUGINS

src/lib/systemd/Watchdog.cxx

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2018 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "Watchdog.hxx"
+
+#include <systemd/sd-daemon.h>
+
+namespace Systemd {
+
+Watchdog::Watchdog(EventLoop &_loop) noexcept
+	:timer(_loop, BIND_THIS_METHOD(OnTimer))
+{
+	uint64_t usec;
+	if (sd_watchdog_enabled(true, &usec) <= 0)
+		return;
+
+	interval = std::chrono::microseconds(usec) / 2;
+	timer.Schedule(interval);
+}
+
+void
+Watchdog::OnTimer() noexcept
+{
+	sd_notify(0, "WATCHDOG=1");
+	timer.Schedule(interval);
+}
+
+} // namespace Systemd

src/lib/systemd/Watchdog.hxx

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2018 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef SYSTEMD_WATCHDOG_HXX
+#define SYSTEMD_WATCHDOG_HXX
+
+#include "check.h"
+#include "event/TimerEvent.hxx"
+
+namespace Systemd {
+
+/**
+ * This class implements the systemd watchdog protocol; see
+ * systemd.service(5) and sd_watchdog_enabled(3).  If the watchdog is
+ * not enabled, this class does nothing.
+ */
+class Watchdog {
+	TimerEvent timer;
+
+	std::chrono::steady_clock::duration interval;
+
+public:
+	explicit Watchdog(EventLoop &_loop) noexcept;
+
+private:
+	void OnTimer() noexcept;
+};
+
+} // namespace Systemd
+
+#endif

systemd/system/mpd.service.in

@@ -7,6 +7,11 @@ After=network.target sound.target
 Type=notify
 ExecStart=@prefix@/bin/mpd --no-daemon
 
+# Enable this setting to ask systemd to watch over MPD, see
+# systemd.service(5).  This is disabled by default because it causes
+# periodic wakeups which are unnecessary if MPD is not playing.
+#WatchdogSec=120
+
 # allow MPD to use real-time priority 50
 LimitRTPRIO=50
 LimitRTTIME=infinity

systemd/user/mpd.service.in

@@ -7,6 +7,11 @@ After=network.target sound.target
 Type=notify
 ExecStart=@prefix@/bin/mpd --no-daemon
 
+# Enable this setting to ask systemd to watch over MPD, see
+# systemd.service(5).  This is disabled by default because it causes
+# periodic wakeups which are unnecessary if MPD is not playing.
+#WatchdogSec=120
+
 # allow MPD to use real-time priority 50
 LimitRTPRIO=50
 LimitRTTIME=infinity