Provide means to ensure a JPMS module can read dynamically defined classes

Author: mcculls

utils/src/main/java/datadog/instrument/utils/Modules.java

@@ -0,0 +1,50 @@
+/*
+ * Unless explicitly stated otherwise all files in this repository are licensed under the Apache-2.0 License.
+ * This product includes software developed at Datadog (https://www.datadoghq.com/).
+ * Copyright 2025-Present Datadog, Inc.
+ */
+
+package datadog.instrument.utils;
+
+import static datadog.instrument.utils.JVM.atLeastJava;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.emptySet;
+
+import java.lang.instrument.Instrumentation;
+import java.util.HashSet;
+import java.util.Set;
+
+/** Methods for managing <a href="https://openjdk.org/projects/jigsaw/spec/">JPMS</a> modules. */
+public final class Modules {
+
+  /**
+   * Ensures the module has read access to classes dynamically defined in the given class-loaders.
+   *
+   * @param inst the instrumentation that can redefine modules
+   * @param module the module that should be able to read the classes
+   * @param classLoaders the class-loaders defining classes to read
+   */
+  @SuppressWarnings({"Since15"})
+  public static void ensureReadability(
+      Instrumentation inst, Object module, Iterable<ClassLoader> classLoaders) {
+    if (atLeastJava(9)) { // JPMS is only available on Java 9+
+      if (!(module instanceof java.lang.Module)) {
+        return; // argument is not a real module
+      }
+      java.lang.Module theModule = (java.lang.Module) module;
+      if (!theModule.isNamed()) {
+        return; // unnamed modules can read each other
+      }
+      Set<java.lang.Module> extraReads = new HashSet<>();
+      for (ClassLoader cl : classLoaders) {
+        java.lang.Module unnamedModule = cl.getUnnamedModule();
+        if (!theModule.canRead(unnamedModule)) {
+          extraReads.add(unnamedModule);
+        }
+      }
+      if (!extraReads.isEmpty()) {
+        inst.redefineModule(theModule, extraReads, emptyMap(), emptyMap(), emptySet(), emptyMap());
+      }
+    }
+  }
+}