Extend JVM metrics with thread states (#391)

Signed-off-by: Christian Stein <[email protected]>

Author: Christian Stein

simpleclient_hotspot/src/main/java/io/prometheus/client/hotspot/ThreadExports.java

@@ -5,9 +5,13 @@
 import io.prometheus.client.GaugeMetricFamily;
 
 import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadInfo;
 import java.lang.management.ThreadMXBean;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 /**
  * Exports metrics about JVM thread areas.
@@ -73,6 +77,40 @@ void addThreadMetrics(List<MetricFamilySamples> sampleFamilies) {
         "jvm_threads_deadlocked_monitor",
         "Cycles of JVM-threads that are in deadlock waiting to acquire object monitors",
         nullSafeArrayLength(threadBean.findMonitorDeadlockedThreads())));
+
+    GaugeMetricFamily threadStateFamily = new GaugeMetricFamily(
+      "jvm_threads_state",
+      "Current count of threads by state",
+      Collections.singletonList("state"));
+
+    Map<Thread.State, Integer> threadStateCounts = getThreadStateCountMap();
+    for (Map.Entry<Thread.State, Integer> entry : threadStateCounts.entrySet()) {
+      threadStateFamily.addMetric(
+        Collections.singletonList(entry.getKey().toString()),
+        entry.getValue()
+      );
+    }
+  }
+
+  private Map<Thread.State, Integer> getThreadStateCountMap() {
+    // Get thread information without computing any stack traces
+    ThreadInfo[] allThreads = threadBean.getThreadInfo(threadBean.getAllThreadIds(), 0);
+
+    // Initialize the map with all thread states
+    HashMap<Thread.State, Integer> threadCounts = new HashMap<Thread.State, Integer>();
+    for (Thread.State state : Thread.State.values()) {
+      threadCounts.put(state, 0);
+    }
+
+    // Collect the actual thread counts
+    for (ThreadInfo curThread : allThreads) {
+      if (curThread != null) {
+        Thread.State threadState = curThread.getThreadState();
+        threadCounts.put(threadState, threadCounts.get(threadState) + 1);
+      }
+    }
+
+    return threadCounts;
   }
 
   private static double nullSafeArrayLength(long[] array) {

simpleclient_hotspot/src/test/java/io/prometheus/client/hotspot/ThreadExportsTest.java

@@ -5,6 +5,7 @@
 import org.junit.Test;
 import org.mockito.Mockito;
 
+import java.lang.management.ThreadInfo;
 import java.lang.management.ThreadMXBean;
 
 import static org.junit.Assert.assertEquals;
@@ -26,6 +27,8 @@ public void setUp() {
     when(mockThreadsBean.getTotalStartedThreadCount()).thenReturn(503L);
     when(mockThreadsBean.findDeadlockedThreads()).thenReturn(new long[]{1L,2L,3L});
     when(mockThreadsBean.findMonitorDeadlockedThreads()).thenReturn(new long[]{2L,3L,4L});
+    when(mockThreadsBean.getAllThreadIds()).thenReturn(new long[]{3L,4L,5L});
+    when(mockThreadsBean.getThreadInfo(new long[]{3L,4L,5L}, 0)).thenReturn(new ThreadInfo[] {});
     collectorUnderTest = new ThreadExports(mockThreadsBean).register(registry);
   }