Ensure the list of forbidden modules for layered images is always complete when accessed

Author: Zeavee

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java

@@ -43,6 +43,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiPredicate;
 import java.util.function.BooleanSupplier;
 import java.util.function.Predicate;
@@ -265,7 +266,8 @@ public enum UsageKind {
      * Some modules contain native methods that should never be in the image, as they are either
      * hosted only, or currently unsupported in layered images.
      */
-    private final Set<Module> forbiddenModules = new HashSet<>();
+    protected final Set<Module> forbiddenModules = new HashSet<>();
+    protected final AtomicBoolean initializedForbiddenModules = new AtomicBoolean();
 
     @SuppressWarnings("this-escape")
     public SVMHost(OptionValues options, ImageClassLoader loader, ClassInitializationSupport classInitializationSupport, AnnotationSubstitutionProcessor annotationSubstitutions,
@@ -1550,7 +1552,7 @@ public ConstantExpressionRegistry getConstantExpressionRegistry() {
 
     @Override
     public Set<Module> getForbiddenModules() {
-        if (forbiddenModules.isEmpty()) {
+        if (!initializedForbiddenModules.get()) {
             forbiddenModules.add(JVMCI.class.getModule());
             Class<?> llvm = ReflectionUtil.lookupClass(true, "com.oracle.svm.shadowed.org.bytedeco.llvm.global.LLVM");
             if (llvm != null) {
@@ -1569,6 +1571,7 @@ public Set<Module> getForbiddenModules() {
                 forbiddenModules.add(libGraal.getModule());
             }
         }
+        initializedForbiddenModules.set(true);
         return forbiddenModules;
     }
 }