From 496dfa3b15106c7d2ff08dfbb380fad4e7c91d69 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Xavier=20L=C3=A9aut=C3=A9?= <xvrl@apache.org>
Date: Sun, 25 Aug 2019 08:26:58 -0400
Subject: [PATCH] fix JVMMonitor initialization with JDK11 (#8397)

JVMMonitor requires access to jdk.internal.perf.Perf to enable GC
counters, which requires additional JVM arguments with JDK11.

This change adds a fallback in case GC counters cannot be initialized,
and logs a warning message explaining how GC counters can be enabled.
---
 .../druid/java/util/metrics/JvmMonitor.java   | 31 +++++++++++++++++--
 .../java/util/metrics/JvmMonitorTest.java     |  3 ++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/org/apache/druid/java/util/metrics/JvmMonitor.java b/core/src/main/java/org/apache/druid/java/util/metrics/JvmMonitor.java
index 118ed315eee..2309139e176 100644
--- a/core/src/main/java/org/apache/druid/java/util/metrics/JvmMonitor.java
+++ b/core/src/main/java/org/apache/druid/java/util/metrics/JvmMonitor.java
@@ -19,9 +19,11 @@
 
 package org.apache.druid.java.util.metrics;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
 import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.java.util.emitter.service.ServiceEmitter;
 import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
 import org.gridkit.lab.jvm.perfdata.JStatData;
@@ -29,6 +31,7 @@ import org.gridkit.lab.jvm.perfdata.JStatData.LongCounter;
 import org.gridkit.lab.jvm.perfdata.JStatData.StringCounter;
 import org.gridkit.lab.jvm.perfdata.JStatData.TickCounter;
 
+import javax.annotation.Nullable;
 import java.lang.management.BufferPoolMXBean;
 import java.lang.management.ManagementFactory;
 import java.lang.management.MemoryPoolMXBean;
@@ -40,11 +43,16 @@ import java.util.Map;
 
 public class JvmMonitor extends FeedDefiningMonitor
 {
+  private static final Logger log = new Logger(JvmMonitor.class);
+
   private final Map<String, String[]> dimensions;
   private final long pid;
 
-  private final GcCounters gcCounters = new GcCounters();
+  @VisibleForTesting
+  @Nullable
+  final GcCounters gcCounters;
 
+  @Nullable
   private final AllocationMetricCollector collector;
 
   public JvmMonitor()
@@ -69,6 +77,7 @@ public class JvmMonitor extends FeedDefiningMonitor
     this.dimensions = ImmutableMap.copyOf(dimensions);
     this.pid = Preconditions.checkNotNull(pidDiscoverer).getPid();
     this.collector = AllocationMetricCollectors.getAllocationMetricCollector();
+    this.gcCounters = tryCreateGcCounters();
   }
 
   @Override
@@ -146,7 +155,25 @@ public class JvmMonitor extends FeedDefiningMonitor
 
   private void emitGcMetrics(ServiceEmitter emitter)
   {
-    gcCounters.emit(emitter, dimensions);
+    if (gcCounters != null) {
+      gcCounters.emit(emitter, dimensions);
+    }
+  }
+
+  @Nullable
+  private GcCounters tryCreateGcCounters()
+  {
+    try {
+      return new GcCounters();
+    }
+    catch (RuntimeException e) {
+      // in JDK11 jdk.internal.perf.Perf is not accessible, unless
+      // --add-exports java.base/jdk.internal.perf=ALL-UNNAMED is set
+      log.warn("Cannot initialize GC counters. If running JDK11 and above,"
+               + " add --add-exports java.base/jdk.internal.perf=ALL-UNNAMED"
+               + " to the JVM arguments to enable GC counters.");
+    }
+    return null;
   }
 
   /**
diff --git a/core/src/test/java/org/apache/druid/java/util/metrics/JvmMonitorTest.java b/core/src/test/java/org/apache/druid/java/util/metrics/JvmMonitorTest.java
index a1dead94edc..1e5cff5016b 100644
--- a/core/src/test/java/org/apache/druid/java/util/metrics/JvmMonitorTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/metrics/JvmMonitorTest.java
@@ -24,6 +24,7 @@ import org.apache.druid.java.util.emitter.core.Event;
 import org.apache.druid.java.util.emitter.service.ServiceEmitter;
 import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
 import org.junit.Assert;
+import org.junit.Assume;
 import org.junit.Test;
 
 import java.util.List;
@@ -39,6 +40,8 @@ public class JvmMonitorTest
     final ServiceEmitter serviceEmitter = new ServiceEmitter("test", "localhost", emitter);
     serviceEmitter.start();
     final JvmMonitor jvmMonitor = new JvmMonitor();
+    // skip tests if gc counters fail to initialize with this JDK
+    Assume.assumeNotNull(jvmMonitor.gcCounters);
 
     while (true) {
       // generate some garbage to see gc counters incremented