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

/*
 * 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
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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");
        }
    }
}