/*
 *
 *  * Copyright 2020 New Relic Corporation. All rights reserved.
 *  * SPDX-License-Identifier: Apache-2.0
 *
 */

package com.newrelic.weave.utils;

import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.tree.InnerClassNode;

/**
 * This class exists only to work around the fact that InnerClassNode instances are NOT thread safe. If multiple threads
 * call {@link #accept(ClassVisitor)} at the same time there is a race condition that exists that has been shown to
 * cause VerifyErrors and other serious bytecode-related exceptions.
 * <p>
 * By synchronizing on the {@link #accept(ClassVisitor)} method we are ensuring that any usage of this InnerClassNode in
 * the agent can be accessed by multiple threads. One important thing to note is that this ties us pretty strongly to an
 * ASM version due to the fact that we had to override constructors in the original asm class. If these constructors
 * change or other accept() methods are added we will need to update accordingly.
 * <p>
 * NOTE: If you are upgrading from org.ow2.asm:asm / org.ow2.asm:asm-tree make sure to double-check that this class hasn't changed between versions.
 */
public class SynchronizedInnerClassNode extends InnerClassNode {

    public SynchronizedInnerClassNode(String name, String outerName, String innerName, int access) {
        super(name, outerName, innerName, access);
    }

    /**
     * This method is synchronized in order to prevent issues with bytecode modification that
     * occur when multiple threads call accept on the same InnerClassNode instance.
     */
    @Override
    public synchronized void accept(ClassVisitor cv) {
        super.accept(cv);
    }

}
