Use javaagent to determine if logger class is initialized in test

dd-java-agent-ittests/src/test/groovy/datadog/trace/agent/CustomLogManagerTest.groovy

@@ -21,11 +21,12 @@ class CustomLogManagerTest extends Specification {
         break
       }
     }
+    final URL customAgent = IntegrationTestUtils.createJarWithClasses(LogManagerSetter.getName(), LogManagerSetter)
 
     expect:
     agentArg != null
     IntegrationTestUtils.runOnSeparateJvm(LogManagerSetter.getName()
-      , [agentArg, "-Ddd.jmxfetch.enabled=true"] as String[]
+      , [agentArg, "-javaagent:" + customAgent.getPath(), "-Ddd.jmxfetch.enabled=true"] as String[]
       , "" as String[]
       , true) == 0
   }

dd-java-agent-ittests/src/test/java/datadog/trace/agent/test/IntegrationTestUtils.java

@@ -19,6 +19,7 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.Callable;
+import java.util.jar.Attributes;
 import java.util.jar.JarEntry;
 import java.util.jar.JarOutputStream;
 import java.util.jar.Manifest;
@@ -77,20 +78,32 @@ public class IntegrationTestUtils {
     }
   }
 
+  /** See {@link IntegrationTestUtils#createJarWithClasses(String, Class[])} */
+  public static URL createJarWithClasses(final Class<?>... classes) throws IOException {
+    return createJarWithClasses(null, classes);
+  }
   /**
    * Create a temporary jar on the filesystem with the bytes of the given classes.
    *
    * <p>The jar file will be removed when the jvm exits.
    *
+   * @param mainClassname The name of the class to use for Main-Class and Premain-Class. May be null
    * @param classes classes to package into the jar.
    * @return the location of the newly created jar.
    * @throws IOException
    */
-  public static URL createJarWithClasses(final Class<?>... classes) throws IOException {
+  public static URL createJarWithClasses(final String mainClassname, final Class<?>... classes)
+      throws IOException {
     final File tmpJar = File.createTempFile(UUID.randomUUID().toString() + "-", ".jar");
     tmpJar.deleteOnExit();
 
     final Manifest manifest = new Manifest();
+    if (mainClassname != null) {
+      Attributes mainAttributes = manifest.getMainAttributes();
+      mainAttributes.put(Attributes.Name.MANIFEST_VERSION, "1.0");
+      mainAttributes.put(Attributes.Name.MAIN_CLASS, mainClassname);
+      mainAttributes.put(new Attributes.Name("Premain-Class"), mainClassname);
+    }
     final JarOutputStream target = new JarOutputStream(new FileOutputStream(tmpJar), manifest);
     for (final Class<?> clazz : classes) {
       addToJar(clazz, target);

dd-java-agent-ittests/src/test/java/jvmbootstraptest/LogManagerSetter.java

@@ -1,6 +1,10 @@
 package jvmbootstraptest;
 
-import java.lang.reflect.Method;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.LogManager;
 
 public class LogManagerSetter {
@@ -8,22 +12,38 @@ public class LogManagerSetter {
   // loggerClassName = java.util.logging.Logger
   private static final String loggerClassName =
       "java.util.logging.TMP".replaceFirst("TMP", "Logger");
+  private static final String loggerInternalName = loggerClassName.replace('.', '/');
+  private static final AtomicBoolean loggerInitialized = new AtomicBoolean(false);
+
+  public static void premain(final String agentArgs, final Instrumentation inst) throws Exception {
+    inst.addTransformer(
+        new ClassFileTransformer() {
+          @Override
+          public byte[] transform(
+              ClassLoader loader,
+              String className,
+              Class<?> classBeingRedefined,
+              ProtectionDomain protectionDomain,
+              byte[] classfileBuffer)
+              throws IllegalClassFormatException {
+            if (loggerInternalName.equals(className)) {
+              loggerInitialized.compareAndSet(false, true);
+            }
+            return null;
+          }
+        });
+  }
 
   public static void main(String... args) throws Exception {
     final ClassLoader systemLoader = ClassLoader.getSystemClassLoader();
 
     // once the logger class has been initialized, we know jmxfetch is running and can proceed with
     // the test
-    final Method method =
-        ClassLoader.class.getDeclaredMethod("findBootstrapClassOrNull", String.class);
-    try {
-      method.setAccessible(true);
-      while (method.invoke(systemLoader, loggerClassName) == null) {
-        Thread.sleep(1);
-      }
-    } finally {
-      method.setAccessible(false);
+    while (!loggerInitialized.get()) {
+      Thread.sleep(1);
     }
+    systemLoader.loadClass(loggerClassName);
+    // at this point the logger is loaded and fully initialized
 
     System.setProperty("java.util.logging.manager", CustomLogManager.class.getName());
     customAssert(