Initialization hooks

instrumentation/src/main/java/io/opentelemetry/android/OpenTelemetryRumBuilder.java

@@ -17,9 +17,11 @@
 import io.opentelemetry.android.instrumentation.network.NetworkAttributesSpanAppender;
 import io.opentelemetry.android.instrumentation.network.NetworkChangeMonitor;
 import io.opentelemetry.android.instrumentation.startup.InitializationEvents;
+import io.opentelemetry.android.instrumentation.startup.InitializationListener;
 import io.opentelemetry.android.instrumentation.startup.SdkInitializationEvents;
 import io.opentelemetry.android.internal.features.persistence.DiskManager;
 import io.opentelemetry.android.internal.features.persistence.SimpleTemporaryFileProvider;
+import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.api.baggage.propagation.W3CBaggagePropagator;
 import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
 import io.opentelemetry.context.propagation.ContextPropagators;
@@ -249,6 +251,7 @@ public SessionId getSessionId() {
      * @return A new {@link OpenTelemetryRum} instance.
      */
     public OpenTelemetryRum build() {
+        notifyInitializationStart();
 
         applyConfiguration();
 
@@ -263,9 +266,23 @@ public OpenTelemetryRum build() {
         SdkPreconfiguredRumBuilder delegate =
                 new SdkPreconfiguredRumBuilder(application, sdk, sessionId);
         instrumentationInstallers.forEach(delegate::addInstrumentation);
+
+        notifyInitializationEnd(sdk);
         return delegate.build();
     }
 
+    private void notifyInitializationStart() {
+        for (InitializationListener listener : config.getInitializationListeners()) {
+            listener.onStart();
+        }
+    }
+
+    private void notifyInitializationEnd(OpenTelemetry openTelemetry) {
+        for (InitializationListener listener : config.getInitializationListeners()) {
+            listener.onEnd(openTelemetry);
+        }
+    }
+
     /** Leverage the configuration to wire up various instrumentation components. */
     private void applyConfiguration() {
         if (config.shouldGenerateSdkInitializationEvents()) {

instrumentation/src/main/java/io/opentelemetry/android/config/OtelRumConfig.java

@@ -7,7 +7,12 @@
 
 import io.opentelemetry.android.ScreenAttributesSpanProcessor;
 import io.opentelemetry.android.instrumentation.network.CurrentNetworkProvider;
+import io.opentelemetry.android.instrumentation.startup.InitializationListener;
 import io.opentelemetry.api.common.Attributes;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.function.Supplier;
 
 /**
@@ -23,7 +28,9 @@ public class OtelRumConfig {
     private boolean includeScreenAttributes = true;
     private DiskBufferingConfiguration diskBufferingConfiguration =
             DiskBufferingConfiguration.builder().build();
+
     private boolean networkChangeMonitoringEnabled = true;
+    private final Set<InitializationListener> initializationListeners = new HashSet<>();
 
     /**
      * Configures the set of global attributes to emit with every span and event. Any existing
@@ -119,4 +126,17 @@ public void disableNetworkChangeMonitoring() {
     public boolean isNetworkChangeMonitoringEnabled() {
         return this.networkChangeMonitoringEnabled;
     }
+
+    /** Adds a new initialization listener. It will be called during the RUM initialization. */
+    public void addInitializationListener(InitializationListener listener) {
+        initializationListeners.add(listener);
+    }
+
+    /**
+     * Provides an unmodifiable list of initialization listeners. This is mean to be called during
+     * RUM initialization.
+     */
+    public Collection<InitializationListener> getInitializationListeners() {
+        return Collections.unmodifiableCollection(initializationListeners);
+    }
 }

instrumentation/src/main/java/io/opentelemetry/android/instrumentation/startup/InitializationListener.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.android.instrumentation.startup
+
+import io.opentelemetry.api.OpenTelemetry
+
+/**
+ * Provides callbacks to know the sate of the initialization.
+ */
+interface InitializationListener {
+    /**
+     * Called when the RUM initialization starts.
+     */
+    fun onStart()
+
+    /**
+     * Called when the RUM initialization ends.
+     * @param openTelemetry - The initialized OpenTelemetry instance.
+     */
+    fun onEnd(openTelemetry: OpenTelemetry)
+}