Add continuous profiling and update telemetry for Illuminate

CHANGELOG.md

@@ -2,6 +2,19 @@
 
 ## Unreleased
 
+### Enhancements
+
+* Add continuous profiling (`enableContinuousProfiling`, `continuousProfilingMaxAgeSeconds`) which
+  keeps a single JFR recording running in a circular buffer so profile requests dump the most recent
+  window of data immediately
+  ([#4807](https://github.com/microsoft/ApplicationInsights-Java/pull/4807))
+
+### Breaking changes
+
+* Rename the `MachineStats` JFR diagnostic event to `MachineInfo`. Custom `.jfc` files that enable
+  `com.microsoft.applicationinsights.diagnostics.jfr.MachineStats` must be updated to the new event
+  name ([#4807](https://github.com/microsoft/ApplicationInsights-Java/pull/4807))
+
 ## Version 3.7.9 GA (06/18/2026)
 
 ### Enhancements

agent/agent-profiler/agent-diagnostics-api/src/main/java/com/microsoft/applicationinsights/diagnostics/DiagnosticEngine.java

@@ -17,4 +17,24 @@ public interface DiagnosticEngine {
    * alertBreach.alertConfiguration.profileDuration
    */
   Future<DiagnosisResult<?>> performDiagnosis(AlertBreach alertBreach);
+
+  /**
+   * Start collecting diagnostics continuously.
+   *
+   * <p>Used with continuous profiling, where a circular buffer is dumped on demand rather than a
+   * forward-looking recording being created per breach. Registering the periodic diagnostic
+   * emitters up front ensures diagnostic events populate the continuous recording buffer, so they
+   * are present in any snapshot that is dumped.
+   *
+   * @return {@code true} if continuous diagnostics were started successfully; {@code false} if this
+   *     engine does not support continuous diagnostics or startup failed. The default
+   *     implementation returns {@code false} so alternate implementations do not silently appear to
+   *     support continuous diagnostics while doing nothing.
+   */
+  default boolean startContinuousDiagnostics() {
+    return false;
+  }
+
+  /** Stop collecting diagnostics continuously. Defaults to a no-op. */
+  default void stopContinuousDiagnostics() {}
 }

agent/agent-profiler/agent-diagnostics-jfr/src/main/java/com/microsoft/applicationinsights/diagnostics/jfr/MachineInfo.java

@@ -0,0 +1,117 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.microsoft.applicationinsights.diagnostics.jfr;
+
+import com.azure.json.JsonReader;
+import com.azure.json.JsonSerializable;
+import com.azure.json.JsonToken;
+import com.azure.json.JsonWriter;
+import java.io.IOException;
+import jdk.jfr.Category;
+import jdk.jfr.Description;
+import jdk.jfr.Event;
+import jdk.jfr.Label;
+import jdk.jfr.Name;
+import jdk.jfr.Period;
+import jdk.jfr.StackTrace;
+
+/**
+ * Machine-level diagnostic event.
+ *
+ * <p><b>Compatibility contract.</b> The JFR wire event name ({@link #NAME}) is an explicitly
+ * versioned identifier. It was renamed from {@link #LEGACY_NAME} ("MachineStats") to "MachineInfo".
+ * Because the event name is the key by which a reader locates the event, changing it is a
+ * compatibility boundary that {@link #SCHEMA_VERSION} (payload versioning) cannot bridge:
+ *
+ * <ul>
+ *   <li><b>Read side (backward compatibility):</b> readers must look up {@link #NAME} and fall back
+ *       to {@link #LEGACY_NAME} so that recordings produced by older agents (which carry a
+ *       "MachineStats" event) can still be discovered and scored.
+ *   <li><b>Write side (forward compatibility):</b> agents at this version and later emit only
+ *       {@link #NAME}. Consumers/backends and any custom JFC files must therefore be updated to
+ *       recognize "MachineInfo"; older consumers that only know "MachineStats" will not find the
+ *       event. This is a deliberate, documented minimum-consumer-version requirement rather than a
+ *       silent change.
+ * </ul>
+ *
+ * <p>Once the write side no longer needs to interoperate with the old name, {@link #LEGACY_NAME}
+ * and its read-side fallback can be removed.
+ */
+@SuppressWarnings("Java8ApiChecker") // JFR APIs require Java 11+, but agent targets Java 8 bytecode
+@Name("com.microsoft.applicationinsights.diagnostics.jfr.MachineInfo")
+@Label("MachineInfo")
+@Category("Diagnostic")
+@Description("MachineInfo")
+@StackTrace(false)
+@Period("beginChunk")
+public class MachineInfo extends Event implements JsonSerializable<MachineInfo> {
+  public static final String NAME = "com.microsoft.applicationinsights.diagnostics.jfr.MachineInfo";
+
+  /**
+   * Event name emitted by agents prior to the MachineStats-&gt;MachineInfo rename. Readers fall
+   * back to this so previously-recorded recordings (which carry a "MachineStats" event) can still
+   * be located and scored.
+   */
+  public static final String LEGACY_NAME =
+      "com.microsoft.applicationinsights.diagnostics.jfr.MachineStats";
+
+  /**
+   * Current schema version. Version 2 drops the legacy {@code contextSwitchesPerMs} field;
+   * recordings produced before the schemaVersion field was added carry schemaVersion 1 (the
+   * implicit legacy version) and still serialize {@code contextSwitchesPerMs}.
+   */
+  public static final int SCHEMA_VERSION = 2;
+
+  private int coreCount;
+
+  private int schemaVersion;
+
+  public int getCoreCount() {
+    return coreCount;
+  }
+
+  public MachineInfo setCoreCount(int coreCount) {
+    this.coreCount = coreCount;
+    return this;
+  }
+
+  public int getSchemaVersion() {
+    return schemaVersion;
+  }
+
+  public MachineInfo setSchemaVersion(int schemaVersion) {
+    this.schemaVersion = schemaVersion;
+    return this;
+  }
+
+  @Override
+  public JsonWriter toJson(JsonWriter jsonWriter) throws IOException {
+    jsonWriter.writeStartObject();
+    return jsonWriter
+        .writeIntField("coreCount", coreCount)
+        .writeIntField("schemaVersion", schemaVersion)
+        .writeEndObject();
+  }
+
+  public static MachineInfo fromJson(JsonReader jsonReader) throws IOException {
+    return jsonReader.readObject(
+        reader -> {
+          MachineInfo deserializedValue = new MachineInfo();
+
+          while (reader.nextToken() != JsonToken.END_OBJECT) {
+            String fieldName = reader.getFieldName();
+            reader.nextToken();
+            if ("coreCount".equals(fieldName)) {
+              deserializedValue.setCoreCount(reader.getInt());
+            } else if ("schemaVersion".equals(fieldName)) {
+              deserializedValue.setSchemaVersion(reader.getInt());
+            } else {
+              reader.skipChildren();
+            }
+          }
+
+          return deserializedValue;
+        });
+  }
+}

agent/agent-profiler/agent-diagnostics/build.gradle.kts

@@ -18,4 +18,9 @@ dependencies {
 
   compileOnly("com.google.auto.service:auto-service")
   annotationProcessor("com.google.auto.service:auto-service")
+
+  testImplementation("org.assertj:assertj-core")
+  testImplementation("org.mockito:mockito-core")
+  testImplementation("org.gradle.jfr.polyfill:jfr-polyfill:1.0.2")
+  testImplementation("com.azure:azure-json")
 }