private Object getValue(Monitor<?> monitor, boolean reset) {
   try {
     if (limiter != null) {
       final MonitorValueCallable c = new MonitorValueCallable(monitor);
       return limiter.callWithTimeout(c, 1, TimeUnit.SECONDS, true);
     } else {
       return monitor.getValue();
     }
   } catch (UncheckedTimeoutException e) {
     LOGGER.warn("timeout trying to get value for {}", monitor.getConfig());
   } catch (Exception e) {
     LOGGER.warn("failed to get value for " + monitor.getConfig(), e);
   }
   return null;
 }
 private void getMonitors(List<Monitor<?>> monitors, MetricFilter filter, Monitor<?> monitor) {
   if (monitor instanceof CompositeMonitor<?>) {
     for (Monitor<?> m : ((CompositeMonitor<?>) monitor).getMonitors()) {
       getMonitors(monitors, filter, m);
     }
   } else if (filter.matches(monitor.getConfig())) {
     monitors.add(monitor);
   }
 }
 /** {@inheritDoc} */
 public List<Metric> poll(MetricFilter filter, boolean reset) {
   refreshMonitorCache(filter);
   List<Monitor<?>> monitors = cachedMonitors.get();
   List<Metric> metrics = Lists.newArrayListWithCapacity(monitors.size());
   for (Monitor<?> monitor : monitors) {
     Object v = getValue(monitor, reset);
     if (v != null) {
       long now = System.currentTimeMillis();
       metrics.add(new Metric(monitor.getConfig(), now, v));
     }
   }
   return metrics;
 }
 private void refreshMonitorCache(MetricFilter filter) {
   final long age = System.currentTimeMillis() - cacheLastUpdateTime.get();
   if (age > cacheTTL) {
     List<Monitor<?>> monitors = Lists.newArrayList();
     for (Monitor<?> monitor : registry.getRegisteredMonitors()) {
       try {
         getMonitors(monitors, filter, monitor);
       } catch (Exception e) {
         LOGGER.warn("failed to get monitors for composite " + monitor.getConfig(), e);
       }
     }
     cacheLastUpdateTime.set(System.currentTimeMillis());
     cachedMonitors.set(monitors);
     LOGGER.debug(
         "cache refreshed, {} monitors matched filter, previous age {} seconds",
         monitors.size(),
         age / 1000);
   } else {
     LOGGER.debug(
         "cache age of {} seconds is within ttl of {} seconds", age / 1000, cacheTTL / 1000);
   }
 }