svm: make "JDK-8354897: Support Soft/Weak Reference in AOT cache" work on JDK 21

Author: zapster

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/ReferenceInternals.java

@@ -30,6 +30,7 @@
 import java.lang.ref.Reference;
 import java.lang.ref.SoftReference;
 
+import jdk.graal.compiler.serviceprovider.JavaVersionUtil;
 import org.graalvm.word.Pointer;
 
 import com.oracle.svm.core.NeverInline;
@@ -161,7 +162,8 @@ public static <T> void setNextDiscovered(Reference<T> instance, Reference<?> new
     }
 
     public static boolean hasQueue(Reference<?> instance) {
-        return cast(instance).queue != Target_java_lang_ref_ReferenceQueue.NULL_QUEUE;
+        return cast(instance).queue != (JavaVersionUtil.JAVA_SPEC > 21 ? Target_java_lang_ref_ReferenceQueue.NULL_QUEUE
+                        : Target_java_lang_ref_ReferenceQueue.NULL);
     }
 
     /*
@@ -229,7 +231,8 @@ public static void processPendingReferences() {
                 } else {
                     @SuppressWarnings("unchecked")
                     Target_java_lang_ref_ReferenceQueue<? super Object> queue = SubstrateUtil.cast(ref.queue, Target_java_lang_ref_ReferenceQueue.class);
-                    if (queue != Target_java_lang_ref_ReferenceQueue.NULL_QUEUE) {
+                    if (queue != (JavaVersionUtil.JAVA_SPEC > 21 ? Target_java_lang_ref_ReferenceQueue.NULL_QUEUE
+                                    : Target_java_lang_ref_ReferenceQueue.NULL)) {
                         // Enqueues, avoiding the potentially overridden Reference.enqueue().
                         queue.enqueue(ref);
                     }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/Target_java_lang_ref_Reference.java

@@ -29,6 +29,7 @@
 import java.lang.reflect.Field;
 import java.util.function.BooleanSupplier;
 
+import jdk.graal.compiler.serviceprovider.JavaVersionUtil;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
 import org.graalvm.nativeimage.hosted.FieldValueTransformer;
@@ -119,7 +120,8 @@ public final class Target_java_lang_ref_Reference<T> {
     @Uninterruptible(reason = "The initialization of the fields must be atomic with respect to collection.")
     Target_java_lang_ref_Reference(T referent, Target_java_lang_ref_ReferenceQueue<? super T> queue) {
         this.referent = referent;
-        this.queue = (queue == null) ? Target_java_lang_ref_ReferenceQueue.NULL_QUEUE : queue;
+        this.queue = (queue == null) ? (JavaVersionUtil.JAVA_SPEC > 21 ? Target_java_lang_ref_ReferenceQueue.NULL_QUEUE
+                        : Target_java_lang_ref_ReferenceQueue.NULL) : queue;
     }
 
     @KeepOriginal

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/Target_java_lang_ref_ReferenceQueue.java

@@ -30,10 +30,21 @@
 import com.oracle.svm.core.annotate.Alias;
 import com.oracle.svm.core.annotate.RecomputeFieldValue;
 import com.oracle.svm.core.annotate.TargetClass;
+import com.oracle.svm.core.annotate.TargetElement;
+import com.oracle.svm.core.jdk.JDK21OrEarlier;
+import com.oracle.svm.core.jdk.JDKLatest;
 
 @TargetClass(ReferenceQueue.class)
 final class Target_java_lang_ref_ReferenceQueue<T> {
-    @Alias static Target_java_lang_ref_ReferenceQueue<Object> NULL_QUEUE;
+    // Checkstyle: stop
+    @Alias //
+    @TargetElement(onlyWith = JDKLatest.class) //
+    static Target_java_lang_ref_ReferenceQueue<Object> NULL_QUEUE;
+    // CheckStyle: resume
+
+    @Alias //
+    @TargetElement(onlyWith = JDK21OrEarlier.class) //
+    static Target_java_lang_ref_ReferenceQueue<Object> NULL;
 
     @Alias @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Reset) //
     volatile Reference<? extends T> head;