Systemd Watchdog

SystemdWatchdog.java

import jnr.constants.platform.Signal;
import jnr.ffi.LibraryLoader;
import jnr.posix.POSIX;
import jnr.posix.POSIXFactory;
import jnr.posix.SignalHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class SystemdWatchdog {
    private static final Logger LOGGER = LoggerFactory.getLogger(Main.class);
    private static final POSIX  POSIX  = POSIXFactory.getPOSIX();

    public static void main(String[] args) {
        try {
            final Watchdog wd = new Watchdog();
            final SignalHandler handler = signal ->LOGGER.info("Got signal : " + signal);

            POSIX.signal(Signal.SIGHUP , handler);
            POSIX.signal(Signal.SIGUSR1, handler);
            POSIX.signal(Signal.SIGUSR2, handler);

            wd.start();

            for(int i=0; i<100; i++) {
                LOGGER.info("Sleep ...");
                Thread.sleep(1000);
            }

            wd.stop();

        } catch (Exception e) {

        }
    }

    public static class Watchdog {
        private final ScheduledExecutorService scheduler;

        public Watchdog() {
            this.scheduler = Executors.newScheduledThreadPool(1);
        }

        public void start() throws Exception {
            String timeouts = System.getenv("WATCHDOG_USEC");
            Systemd systemd = LibraryLoader.create(Systemd.class).load("systemd-daemon");

            if(timeouts != null) {
                scheduler.scheduleAtFixedRate(
                    () -> LOGGER.info("Notify {}", systemd.sd_notify(0, "WATCHDOG=1")),
                    0,
                    Long.parseLong(timeouts) / 2,
                    TimeUnit.MICROSECONDS
                );
            }
        }

        public void stop() throws Exception {
            this.scheduler.shutdown();
            this.scheduler.awaitTermination(5, TimeUnit.SECONDS);
        }
    }

    public interface Systemd {
        int sd_notify(int unsetEnvironment, String state);
    }
}