[jira] [Reopened] (BCEL-267) Race conditions on static fields in BranchHandle and InstructionHandle

["Stephan Herrmann (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BCEL-267?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stephan Herrmann reopened BCEL-267:
-----------------------------------

Seeing this unfixed even in version 6.0 implies that BCEL cannot be used during class loading of applications: If thread A loads and transforms class X it can be nuked by thread B loading and transforming class Y.

Given that I provided a fix and the reasoning why this patch is safe I am clueless why this change has not been accepted.

Please re-consider and provide a 6.1 release, otherwise all the work having gone into BCEL 6.0 (thanks!) is useless for real-life use cases.

Please remember that I am *not* requesting full thread-safety, just that BCEL behaves well in a multi-threaded application where clients guarantee isolation based on data.

> 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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