Handle broken FileDescriptorGaugeSet in Java 9

modules/metrics/src/main/java/com/spotify/apollo/metrics/MetricsModule.java

@@ -19,11 +19,14 @@
  */
 package com.spotify.apollo.metrics;
 
+import com.codahale.metrics.Gauge;
+import com.codahale.metrics.Metric;
+import com.codahale.metrics.RatioGauge;
+import com.codahale.metrics.jvm.FileDescriptorRatioGauge;
 import com.google.auto.service.AutoService;
 import com.google.inject.Provides;
 import com.google.inject.Singleton;
 import com.google.inject.multibindings.Multibinder;
-
 import com.spotify.apollo.core.Services;
 import com.spotify.apollo.environment.EndpointRunnableFactoryDecorator;
 import com.spotify.apollo.metrics.semantic.MetricsConfig;
@@ -32,20 +35,20 @@
 import com.spotify.apollo.module.ApolloModule;
 import com.spotify.metrics.core.MetricId;
 import com.spotify.metrics.core.SemanticMetricRegistry;
+import com.spotify.metrics.core.SemanticMetricSet;
 import com.spotify.metrics.ffwd.FastForwardReporter;
 import com.spotify.metrics.jvm.CpuGaugeSet;
-import com.spotify.metrics.jvm.FileDescriptorGaugeSet;
 import com.spotify.metrics.jvm.GarbageCollectorMetricSet;
 import com.spotify.metrics.jvm.MemoryUsageGaugeSet;
 import com.spotify.metrics.jvm.ThreadStatesMetricSet;
-
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
-
 import javax.inject.Named;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Provides bindings to {@link SemanticMetricRegistry} and {@link MetricsFactory}.
@@ -91,7 +94,30 @@ public SemanticMetricRegistry semanticMetricRegistry() {
     metricRegistry.register(MetricId.EMPTY, new GarbageCollectorMetricSet());
     metricRegistry.register(MetricId.EMPTY, new ThreadStatesMetricSet());
     metricRegistry.register(MetricId.EMPTY, CpuGaugeSet.create());
-    metricRegistry.register(MetricId.EMPTY, new FileDescriptorGaugeSet());
+    // FIXME(staffan): FileDescriptorGaugeSet is broken in Java 9 (it throws an exception).
+    // This is a temporary workaround to make it work, by reimplementing the FileDescriptorGaugeSet
+    // from semantic-metrics in a way that properly handles the exception. A more proper fix
+    // would be to fix this upstream (ideally in codahale metrics, possibly in semantic-metrics).
+    metricRegistry.register(MetricId.EMPTY, new SemanticMetricSet() {
+      private FileDescriptorRatioGauge fileDescriptorRatioGauge = new FileDescriptorRatioGauge();
+
+      @Override
+      public Map<MetricId, Metric> getMetrics() {
+        final Map<MetricId, Metric> gauges = new HashMap<>();
+        final MetricId metricId =
+            MetricId.build().tagged("what", "file-descriptor-ratio", "unit", "%");
+        gauges.put(metricId, (Gauge<Object>) () -> {
+          try {
+            return fileDescriptorRatioGauge.getValue();
+          } catch (final Exception ex) {
+            LOG.debug("Failed to get metrics for FileDescriptorGaugeSet", ex);
+            // This is what the upstream FileDescriptorRatioGauge returns when an exception occurs.
+            return RatioGauge.Ratio.of(Double.NaN, Double.NaN);
+          }
+        });
+        return Collections.unmodifiableMap(gauges);
+      }
+    });
 
     return metricRegistry;
   }