[jboss-jira] [JBoss JIRA] Resolved: (JASSIST-86) Make concurrent calls to getRefClasses() safe.

[Shigeru Chiba (JIRA)]

     [ https://jira.jboss.org/jira/browse/JASSIST-86?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Shigeru Chiba resolved JASSIST-86.
----------------------------------

    Fix Version/s: 3.11.0.GA
       Resolution: Done


> Make concurrent calls to getRefClasses() safe.
> ----------------------------------------------
>
>                 Key: JASSIST-86
>                 URL: https://jira.jboss.org/jira/browse/JASSIST-86
>             Project: Javassist
>          Issue Type: Bug
>    Affects Versions: 3.10.0.GA
>            Reporter: Shigeru Chiba
>            Assignee: Shigeru Chiba
>             Fix For: 3.11.0.GA
>
>         Attachments: fix-javassist-concurrency
>
>
> There is a race condition when getRefClasses is called twice concurrently on
> the same class - one of the chains in HashMap for collision resolution can become
> cyclic, i.e. an infinitely long list, causing iteration on the list to enter an
> infinite loop.
> On a CtClass ct, the call path leading to the problem is:
> ct.getRefClasses() -> ct.renameClass() (it's a fake renameClass(), which does
> not rename anything) -> ct.constPool.renameClass()
> One can thus have concurrent calls to ct.constPool.renameClass(); a constPool
> then recreates the internal HashMap, i.e. reinserts again all elements into
> cp.classes (not a temporary map), so we have concurrent accesses to this map.
> In particular, since there can be a collision (as happened for me), the
> collision chain could become cyclic.
> This was found through remote debugging on a concurrent program using Javassist
> (attaching after a series of run-client invocations ended in a crash). It was a
> real-world program, not a client written on purpose to show this.
> This patch solves the problem well, and was tested in a configuration which caused a
> lot of crashes and stopped causing any.
> Lots of better fixes to this could be thought, but they're more invasive.

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