[OPENJPA-2222] Concurrency issue with JPA enhancement in Apache Open JPA

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.2.0
• Component/s: Enhance
• Assignee: Unassigned
• Reporter: Brian DePradine
• Created: 28/Jun/12 20:19
• Updated: 28/Jun/12 20:19

Description

Working Jeremy Bauer, we discovered the following issue:

I think I've figured out what is causing the transformer to return null in some (intermittent) cases. I'm seeing multiple threads [Blueprint Extender: # ] calling into the same PCClassFileTransformer. I've pasted the stack for thread 1 below. I saw an identical instance for a thread 3 - operating on a different persistent class at the same time. This resulted in one of the transforms (per transform method below) returned null.

public byte[] transform(ClassLoader loader, String className,
Class redef, ProtectionDomain domain, byte[] bytes)
throws IllegalClassFormatException {
if (loader == _tmpLoader)
return null;

// JDK bug – OPENJPA-1676
if (className == null)

{ return null; }

---------------------
// prevent re-entrant calls, which can occur if the enhancing
// loader is used to also load OpenJPA libraries; this is to prevent
// recursive enhancement attempts for internal openjpa libraries
if (_transforming)
return null;
---------------------

_transforming = true;

return transform0(className, redef, bytes);
}

Since you use the same transformer on multiple threads we are hitting the condition where there is a transform in progress and you are trying to do another transform on a separate thread.

I spent some time looking at the JPA spec to determine what it says about transformer concurrency and I can't find anything that says that you shouldn't be able to call a transformer in a concurrent manner, hence this defect.