BraveRxJavaSchedulersHook.java

public final class BraveRxJavaSchedulersHook extends RxJavaSchedulersHook {
    @Override
    public Action0 onSchedule(Action0 action) {
        ServerSpanThreadBinder binder = ZipkinHolder.getInstance().serverSpanThreadBinder();
        ServerSpan span = binder.getCurrentServerSpan();
        return () -> {
            binder.setCurrentSpan(span);
            action.call();
        };
    }
}

ZipkinHolder.java

public final class ZipkinHolder {
  
      static {
        System.setProperty(
                "rxjava.plugin.RxJavaSchedulersHook.implementation",
                BraveRxJavaSchedulersHook.class.getCanonicalName());
    }
  
    private static volatile FINNHystrixHooks finnHystrixHooks = new NoopFINNHystrixHooks();

    public static synchronized void registerFINNHystrixHooks(FINNHystrixHooks hooks){
        finnHystrixHooks = hooks;
    }

    private static final Log LOG = LogFactory.getLog(ZipkinHolder.class);

    private static volatile Brave BRAVE;
    
    public static Brave getInstance() {
        if (BRAVE == null) {
            BRAVE = new Brave.Builder(getServiceName())
                    .spanCollector(FailSilentlyCollector.wrap(ZipkinHolder::createSpanCollector))
                    .traceSampler(createSampler())
                    .build();
            setupRx();
        }
        return BRAVE;
    }
    
        private static void setupRx() {
        try {
            LOG.info("Setting up Hystrix and RxJava hools...");
            final RxJavaSchedulersHook hook = RxJavaPlugins.getInstance().getSchedulersHook();
            LOG.info("RxJavaSchedulersHook = " + hook.getClass().getCanonicalName());
            final HystrixConcurrencyStrategy concurrencyStrategy = HystrixPlugins.getInstance().getConcurrencyStrategy();
            LOG.info("HystrixConcurrencyStrategy = " + concurrencyStrategy.getClass().getCanonicalName());
        } catch(IllegalStateException ex) {
            LOG.warn("Couldn't register Hystrix/RX scheduler hooks.", ex);
        }
    }

}

cool stuff!

onSchedule should clear current span in a finally, right?

onSchedule should clear current span in a finally, right?

Probably. This code doen't clean up after itself, it assumes that the next span that is started overwrites the state. (effectively cleaning up after the previous span)