Stephan Herrmann created BCEL-267:
-------------------------------------
Summary: Race conditions on static fields in BranchHandle and
InstructionHandle
Key: BCEL-267
URL: https://issues.apache.org/jira/browse/BCEL-267
Project: Commons BCEL
Issue Type: Bug
Components: Main
Affects Versions: 5.2
Reporter: Stephan Herrmann
I have observed race conditions causing NullPointerException like this
{code}java.lang.NullPointerException
at
org.apache.bcel.generic.InstructionList.getInstructionHandles(InstructionList.java:1021)
at
org.apache.bcel.generic.InstructionList.findHandle(InstructionList.java:141)
at org.apache.bcel.generic.MethodGen.<init>(MethodGen.java:194)
{code}
In the debugger I could verify that concurrent access to the fields
{{BranchHandle.bh_list}} or {{InstructionHandle.ih_list}} can cause corruption
of those lists.
I succeeded to make the exception less frequent by adding synchronized blocks,
but still the exception could be observed. I concluded that for safe protection
the fields would need to be made volatile, which in the end might actually
defeat their original purpose of optimization.
I have since then run with a patched version of BCEL, where those static fields
were simply removed and new Handles were created on every request. This variant
finally was free of the race condition.
Seeing activity towards a 6.0 release, I'd appreciate if this change could be
incorporated.
The original bug tracking my experiments can be found in Eclipse bugzilla:
https://bugs.eclipse.org/344350
The modified classes (based on 5.2) can be found here:
-
http://git.eclipse.org/c/objectteams/org.eclipse.objectteams.git/tree/plugins/org.eclipse.objectteams.otre/bcelpatchsrc/org/apache/bcel/generic
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