The poor Java programmer's alternative to calling sd_notify

java-sd_notify.java

package systemd;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.Paths;
import java.util.function.Supplier;

@lombok.extern.slf4j.Slf4j
public class SdDaemon {
    public static void status(String status) {
        notify("--status=" + status);
    }

    public static void ready() {
        notify("--ready");
    }

    public static boolean booted() {
        return Files.isDirectory(Paths.get("/run/systemd/system"), LinkOption.NOFOLLOW_LINKS);
    }

    private static void notify(String arg) {
        if (!booted() || System.getenv("NOTIFY_SOCKET") == null)
            return;
        try {
            Process p = new ProcessBuilder("systemd-notify", arg)
                .redirectErrorStream(true)
                .start();
            if (ignoreInterruptedException(p::waitFor) == 0)
                return;

            log.error("Failed to notify systemd of/that {}; systemd-notify exited with status {}", arg, p.exitValue());
            try (BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
                r.lines().forEach(l -> log.error("systemd-notify: {}", l));
            }
        } catch (Exception e) {
            log.warn("Failed to notify systemd of service readiness", e);
        }
    }

    private interface ThrowingSupplier<T, E extends Throwable> {
        T get() throws E;
    }

    private static <T> T ignoreInterruptedException(ThrowingSupplier<T, InterruptedException> r) {
        Supplier<Object> s;
        for (;;) {
            try {
                return r.get();
            } catch (InterruptedException e) {
                continue;
            }
        }
    }
}