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From "Stephan Herrmann (JIRA)" <>
Subject [jira] [Reopened] (BCEL-267) Race conditions on static fields in BranchHandle and InstructionHandle
Date Sun, 27 Nov 2016 14:13:58 GMT


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:
>             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(
>         at org.apache.bcel.generic.InstructionList.findHandle(
>         at org.apache.bcel.generic.MethodGen.<init>(
> {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:
> The modified classes (based on 5.2) can be found here:
> -

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