Address review comments

Author: steverao

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/InstrumenterBuilder.java

@@ -24,13 +24,13 @@
 import io.opentelemetry.instrumentation.api.internal.InstrumenterBuilderAccess;
 import io.opentelemetry.instrumentation.api.internal.InstrumenterUtil;
 import io.opentelemetry.instrumentation.api.internal.SchemaUrlProvider;
+import io.opentelemetry.instrumentation.api.internal.ServiceLoaderUtil;
 import io.opentelemetry.instrumentation.api.internal.SpanKey;
 import io.opentelemetry.instrumentation.api.internal.SpanKeyProvider;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.ServiceLoader;
 import java.util.Set;
 import java.util.function.Predicate;
 import java.util.logging.Logger;
@@ -77,10 +77,9 @@ public final class InstrumenterBuilder<REQUEST, RESPONSE> {
       INSTRUMENTATION_CUSTOMIZER_MAP = new HashMap<>();
 
   static {
-    ServiceLoader<InstrumentationCustomizer> serviceLoader =
-        ServiceLoader.load(InstrumentationCustomizer.class);
-
-    for (InstrumentationCustomizer customizer : serviceLoader) {
+    List<InstrumentationCustomizer> customizers =
+        ServiceLoaderUtil.load(InstrumentationCustomizer.class);
+    for (InstrumentationCustomizer customizer : customizers) {
       INSTRUMENTATION_CUSTOMIZER_MAP
           .computeIfAbsent(customizer.instrumentationNamePredicate(), k -> new ArrayList<>())
           .add(customizer);

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/internal/ServiceLoaderUtil.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.api.internal;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.ServiceLoader;
+import java.util.function.Function;
+
+/**
+ * This class is internal and is hence not for public use. Its APIs are unstable and can change at
+ * any time.
+ */
+public final class ServiceLoaderUtil {
+
+  private static Function<Class<?>, List<?>> loaderFunction =
+      clazz -> {
+        List<Object> instances = new ArrayList<>();
+        ServiceLoader<?> serviceLoader = ServiceLoader.load(clazz);
+        for (Object instance : serviceLoader) {
+          instances.add(instance);
+        }
+        return instances;
+      };
+
+  private ServiceLoaderUtil() {
+    // Utility class, no instantiation
+  }
+
+  @SuppressWarnings("unchecked")
+  public static <T> List<T> load(Class<T> clazz) {
+    return (List<T>) loaderFunction.apply(clazz);
+  }
+
+  public static void setLoaderFunction(Function<Class<?>, List<?>> customLoaderFunction) {
+    loaderFunction = customLoaderFunction;
+  }
+}

instrumentation-api/src/test/java/io/opentelemetry/instrumentation/api/instrumenter/InstrumentationCustomizerTest.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.api.instrumenter;
+
+import static io.opentelemetry.sdk.testing.assertj.OpenTelemetryAssertions.assertThat;
+
+import java.util.function.Predicate;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+class InstrumentationCustomizerTest {
+
+  @Mock private AttributesExtractor<Object, Object> attributesExtractor;
+  @Mock private OperationMetrics operationMetrics;
+
+  private InstrumentationCustomizer customizer;
+
+  @BeforeEach
+  @SuppressWarnings("unchecked")
+  void setUp() {
+    customizer =
+        new InstrumentationCustomizer() {
+          @Override
+          public Predicate<String> instrumentationNamePredicate() {
+            return name -> name.startsWith("test.instrumentation");
+          }
+
+          @Override
+          public <REQUEST, RESPONSE>
+              AttributesExtractor<REQUEST, RESPONSE> getAttributesExtractor() {
+            return (AttributesExtractor<REQUEST, RESPONSE>) attributesExtractor;
+          }
+
+          @Override
+          public OperationMetrics getOperationMetrics() {
+            return operationMetrics;
+          }
+        };
+  }
+
+  @Test
+  void testInstrumentationNamePredicate() {
+    assertThat(customizer.instrumentationNamePredicate().test("test.instrumentation.example"))
+        .isTrue();
+    assertThat(customizer.instrumentationNamePredicate().test("other.instrumentation.example"))
+        .isFalse();
+  }
+
+  @Test
+  void testGetAttributesExtractor() {
+    AttributesExtractor<Object, Object> extractor = customizer.getAttributesExtractor();
+    assertThat(extractor).isSameAs(attributesExtractor);
+  }
+
+  @Test
+  void testGetOperationMetrics() {
+    OperationMetrics metrics = customizer.getOperationMetrics();
+    assertThat(metrics).isSameAs(operationMetrics);
+  }
+}

javaagent-bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/AgentInitializer.java

@@ -6,11 +6,15 @@
 package io.opentelemetry.javaagent.bootstrap;
 
 import io.opentelemetry.instrumentation.api.internal.ConfigPropertiesUtil;
+import io.opentelemetry.instrumentation.api.internal.ServiceLoaderUtil;
 import java.io.File;
 import java.lang.instrument.Instrumentation;
 import java.lang.reflect.Constructor;
 import java.security.PrivilegedAction;
 import java.security.PrivilegedExceptionAction;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.ServiceLoader;
 import javax.annotation.Nullable;
 
 /**
@@ -62,6 +66,7 @@ public Void run() {
           public Void run() throws Exception {
             agentClassLoader = createAgentClassLoader("inst", javaagentFile);
             agentStarter = createAgentStarter(agentClassLoader, inst, javaagentFile);
+            setLoaderFunction();
             if (!fromPremain || !delayAgentStart()) {
               agentStarter.start();
               agentStarted = true;
@@ -212,6 +217,19 @@ private static AgentStarter createAgentStarter(
         constructor.newInstance(instrumentation, javaagentFile, isSecurityManagerSupportEnabled);
   }
 
+  /** Sets a custom loader function for the ServiceLoaderUtil to use the agentClassLoader. */
+  private static void setLoaderFunction() {
+    ServiceLoaderUtil.setLoaderFunction(
+        clazz -> {
+          List<Object> instances = new ArrayList<>();
+          ServiceLoader<?> serviceLoader = ServiceLoader.load(clazz, agentClassLoader);
+          for (Object instance : serviceLoader) {
+            instances.add(instance);
+          }
+          return instances;
+        });
+  }
+
   private AgentInitializer() {}
 
   @SuppressWarnings("SystemOut")