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https://issues.apache.org/jira/browse/BCEL-267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16286752#comment-16286752
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Sebb commented on BCEL-267:
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I already wrote that mutable statics are a bad idea [1].
Fixing those is obviously a pre-requisite for using BCEL in multiple threads.
I was just pointing out that whilst that is necessary, it is not sufficient, so
one should not expect it to be a magic bullet.
Even if instances are confined to a single thread, there could be other shared
resources, for example singleton classes or files.
[1]
https://issues.apache.org/jira/browse/BCEL-267?focusedCommentId=14935957&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14935957
> 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
> Attachments:
> BCEL267--Race-conditions-on-static-fields-in-BranchH.patch
>
>
> 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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