8268829: Provide an optimized way to walk the stack with Class object only

8210375: StackWalker::getCallerClass throws UnsupportedOperationException

Reviewed-by: coleenp, dfuchs, bchristi

src/java.base/share/classes/java/lang/ClassFrameInfo.java

@@ -0,0 +1,135 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package java.lang;
+
+import jdk.internal.access.JavaLangInvokeAccess;
+import jdk.internal.access.SharedSecrets;
+import java.lang.StackWalker.StackFrame;
+
+/**
+ * ClassFrameInfo is an implementation of StackFrame that contains only
+ * the class name and declaring class.
+ *
+ * Methods that access the method information such as method name,
+ * will throw UnsupportedOperationException.
+ *
+ * @see StackWalker.Option#DROP_METHOD_INFO
+ */
+class ClassFrameInfo implements StackFrame {
+    static final JavaLangInvokeAccess JLIA = SharedSecrets.getJavaLangInvokeAccess();
+
+    Object classOrMemberName;    // Class or ResolvedMemberName initialized by VM
+    int flags;                   // updated by VM to set hidden and caller-sensitive bits
+
+    /*
+     * Construct an empty ClassFrameInfo object that will be filled by the VM
+     * during stack walking.
+     *
+     * @see StackStreamFactory.AbstractStackWalker#callStackWalk
+     * @see StackStreamFactory.AbstractStackWalker#fetchStackFrames
+     */
+    ClassFrameInfo(StackWalker walker) {
+        this.flags = walker.retainClassRef ? RETAIN_CLASS_REF_BIT : 0;
+    }
+
+    // package-private called by StackStreamFactory to skip
+    // the capability check
+    Class<?> declaringClass() {
+        return (Class<?>) classOrMemberName;
+    }
+
+    boolean isCallerSensitive() {
+        return JLIA.isCallerSensitive(flags & MEMBER_INFO_FLAGS);
+    }
+
+    boolean isHidden() {
+        return JLIA.isHiddenMember(flags & MEMBER_INFO_FLAGS);
+    }
+
+    // ----- implementation of StackFrame methods
+
+    @Override
+    public String getClassName() {
+        return declaringClass().getName();
+    }
+
+    @Override
+    public Class<?> getDeclaringClass() {
+        ensureRetainClassRefEnabled();
+        return declaringClass();
+    }
+
+    @Override
+    public String getMethodName() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int getByteCodeIndex() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public String getFileName() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public int getLineNumber() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean isNativeMethod() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public StackTraceElement toStackTraceElement() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public String toString() {
+        String tags = isHidden() ? " hidden" : "";
+        if (isCallerSensitive()) {
+            tags += " caller sensitive";
+        }
+        return declaringClass().getName() + " " + tags;
+    }
+
+    private static final int MEMBER_INFO_FLAGS = 0x00FFFFFF;
+    private static final int RETAIN_CLASS_REF_BIT = 0x08000000; // retainClassRef
+
+    boolean retainClassRef() {
+        return (flags & RETAIN_CLASS_REF_BIT) == RETAIN_CLASS_REF_BIT;
+    }
+
+    void ensureRetainClassRefEnabled() {
+        if (!retainClassRef()) {
+            throw new UnsupportedOperationException("No access to RETAIN_CLASS_REFERENCE");
+        }
+    }
+}