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

package com.newrelic.weave.utils;

import org.objectweb.asm.ModuleVisitor;
import org.objectweb.asm.tree.ModuleProvideNode;

import java.util.List;

/**
 * This class exists only to work around the fact that ModuleProvideNode instances are NOT thread safe. If multiple threads
 * call {@link #accept(ModuleVisitor)} at the same time there is a race condition that exists that has been shown to
 * cause VerifyErrors and other serious bytecode-related exceptions.
 * 

* By synchronizing on the {@link #accept(ModuleVisitor)} method we are ensuring that any usage of this ModuleProvideNode * 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. *

* 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 SynchronizedModuleProvideNode extends ModuleProvideNode { public SynchronizedModuleProvideNode(final String service, final List providers) { super(service, providers); } /** * This method is synchronized in order to prevent issues with bytecode modification that * occur when multiple threads call accept on the same SynchronizedModuleProvideNode instance. */ public synchronized void accept(final ModuleVisitor mv) { super.accept(mv); } }





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