Add jvm threads instrumentation

instrumentation/runtime-metrics/javaagent/src/main/java/io/opentelemetry/instrumentation/javaagent/runtimemetrics/RuntimeMetricsInstaller.java

@@ -11,6 +11,7 @@
 import io.opentelemetry.instrumentation.runtimemetrics.Classes;
 import io.opentelemetry.instrumentation.runtimemetrics.GarbageCollector;
 import io.opentelemetry.instrumentation.runtimemetrics.MemoryPools;
+import io.opentelemetry.instrumentation.runtimemetrics.Threads;
 import io.opentelemetry.javaagent.extension.AgentListener;
 import io.opentelemetry.javaagent.tooling.config.AgentConfig;
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;
@@ -28,8 +29,9 @@ public void afterAgent(Config config, AutoConfiguredOpenTelemetrySdk unused) {
     if (new AgentConfig(config)
         .isInstrumentationEnabled(Collections.singleton("runtime-metrics"), DEFAULT_ENABLED)) {
 
-      MemoryPools.registerObservers(GlobalOpenTelemetry.get());
       Classes.registerObservers(GlobalOpenTelemetry.get());
+      MemoryPools.registerObservers(GlobalOpenTelemetry.get());
+      Threads.registerObservers(GlobalOpenTelemetry.get());
 
       if (config.getBoolean(
           "otel.instrumentation.runtime-metrics.experimental-metrics.enabled", false)) {

instrumentation/runtime-metrics/javaagent/src/test/groovy/io/opentelemetry/instrumentation/javaagent/runtimemetrics/RuntimeMetricsTest.groovy

@@ -16,15 +16,16 @@ class RuntimeMetricsTest extends AgentInstrumentationSpecification {
 
     then:
     conditions.eventually {
+      assert getMetrics().any { it.name == "process.runtime.jvm.classes.loaded" }
+      assert getMetrics().any { it.name == "process.runtime.jvm.classes.unloaded" }
+      assert getMetrics().any { it.name == "process.runtime.jvm.classes.current_loaded" }
       assert getMetrics().any { it.name == "runtime.jvm.gc.time" }
       assert getMetrics().any { it.name == "runtime.jvm.gc.count" }
       assert getMetrics().any { it.name == "process.runtime.jvm.memory.init" }
       assert getMetrics().any { it.name == "process.runtime.jvm.memory.usage" }
       assert getMetrics().any { it.name == "process.runtime.jvm.memory.committed" }
       assert getMetrics().any { it.name == "process.runtime.jvm.memory.max" }
-      assert getMetrics().any { it.name == "process.runtime.jvm.classes.loaded" }
-      assert getMetrics().any { it.name == "process.runtime.jvm.classes.unloaded" }
-      assert getMetrics().any { it.name == "process.runtime.jvm.classes.current_loaded" }
+      assert getMetrics().any { it.name == "process.runtime.jvm.threads.count" }
     }
   }
 }

instrumentation/runtime-metrics/library/src/main/java/io/opentelemetry/instrumentation/runtimemetrics/Threads.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.runtimemetrics;
+
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.metrics.Meter;
+import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadMXBean;
+
+/**
+ * Registers measurements that generate metrics about JVM threads.
+ *
+ * <p>Example usage:
+ *
+ * <pre>{@code
+ * Classes.registerObservers(GlobalOpenTelemetry.get());
+ * }</pre>
+ *
+ * <p>Example metrics being exported:
+ *
+ * <pre>
+ *   process.runtime.jvm.threads.count 4
+ * </pre>
+ */
+public final class Threads {
+
+  // Visible for testing
+  static final Threads INSTANCE = new Threads();
+
+  /** Register observers for java runtime class metrics. */
+  public static void registerObservers(OpenTelemetry openTelemetry) {
+    INSTANCE.registerObservers(openTelemetry, ManagementFactory.getThreadMXBean());
+  }
+
+  // Visible for testing
+  void registerObservers(OpenTelemetry openTelemetry, ThreadMXBean threadBean) {
+    Meter meter = openTelemetry.getMeter("io.opentelemetry.runtime-metrics");
+
+    meter
+        .upDownCounterBuilder("process.runtime.jvm.threads.count")
+        .setDescription("Number of executing threads")
+        .setUnit("1")
+        .buildWithCallback(
+            observableMeasurement -> observableMeasurement.record(threadBean.getThreadCount()));
+  }
+
+  private Threads() {}
+}

instrumentation/runtime-metrics/library/src/test/java/io/opentelemetry/instrumentation/runtimemetrics/ThreadsTest.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.runtimemetrics;
+
+import static io.opentelemetry.sdk.testing.assertj.OpenTelemetryAssertions.assertThat;
+import static org.mockito.Mockito.when;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.instrumentation.testing.junit.InstrumentationExtension;
+import io.opentelemetry.instrumentation.testing.junit.LibraryInstrumentationExtension;
+import java.lang.management.ThreadMXBean;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+class ThreadsTest {
+
+  @RegisterExtension
+  static final InstrumentationExtension testing = LibraryInstrumentationExtension.create();
+
+  @Mock private ThreadMXBean threadBean;
+
+  @Test
+  void registerObservers() {
+    when(threadBean.getThreadCount()).thenReturn(3);
+
+    Threads.INSTANCE.registerObservers(testing.getOpenTelemetry(), threadBean);
+
+    testing.waitAndAssertMetrics(
+        "io.opentelemetry.runtime-metrics",
+        "process.runtime.jvm.threads.count",
+        metrics ->
+            metrics.anySatisfy(
+                metricData ->
+                    assertThat(metricData)
+                        .hasDescription("Number of executing threads")
+                        .hasUnit("1")
+                        .hasLongSumSatisfying(
+                            sum ->
+                                sum.isNotMonotonic()
+                                    .hasPointsSatisfying(
+                                        point ->
+                                            point.hasValue(3).hasAttributes(Attributes.empty())))));
+  }
+}