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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);
}
}