JCAM or CAMV : Threadsafe?

  • jcamnewbie

    jcamnewbie - 2009-11-09

    Currently I am using JCAM in a manged environment (deployed in WebSphere
    Application Server) and apparently it is not threadsafe.

    JCam processor = new JCam(JCam.Options.VALIDATE, templateDocument,
    xmlDocument, parameters);
    resultDocument = processor.run(orderType);

    Is it s usage issue i.e. the way I am using or it is a design issue?

    Also is CAMV thread safe?

  • Martin Roberts

    Martin Roberts - 2009-11-10

    This is an issue that I have never considered so I really appreciate you
    raising it.

    JCAM is most definitely not ThreadSafe as it changes the Template during the
    validation process so that you HAVE to reread the template file every time it
    is used. This was one of the reasons for considering changing to CAMV. However
    as I have never considered it in CAMV either I am not able to confirm that it
    is Thread safe.

    Can you please explain you usecase for the validation. Are you trying to read
    the Template in once and use it to validate many xml files in different
    threads. In the case of CAMV it would be necessary to make the
    TemplateValidator Thread Safe so that you could use in in many threads. The
    current implementation has some faults in that the errors are held in a static
    list which would get all messed up. I think that your need for it to be Thread
    Safe is a valid change request - even a bug and I will investigate making the
    necessary changes to allow this to happen.

    One of the immediate changes I will try to implement is to remove the use of
    any static variables with in CAMV. I will also remove the use of Static
    functions so that there is no confusion as to which variable is being used. If
    any Static functions remain I will make them Thread safe.

    Thanks again for your very useful input.

  • jcamnewbie

    jcamnewbie - 2009-11-10

    Thanks for the confirmation.
    There are two scenarios here:

    1. As there are multiple threads trying to validate different XMLs concurrently, JCAM started giving multiple errors which are random in nature e.g. NullPointerException, TrimmerException etc.

    2. We are caching the template in memory so that each request need not perform disk io to load it in memory. Understanding was template should be used for "reference" and does not gets modified with each request and should be able to be used by multiple threads.

    Please do let me know if you want me to raise a feature request or bug and for
    which one we can get a fix soon, JCAM or CAMV?

  • Martin Roberts

    Martin Roberts - 2009-11-10

    Sadly, although your assumption would be expected to be correct, in JCAM I use
    the JDOM Libraries to contract and expand the underlying JDOM model of the
    template during processing. This means that the template is not immutable. One
    way round this would be to use the cloning function on the Template Document
    before calling the processor. That way the template you use will be a new copy
    of one each time it is used and in theory should have no links back to the
    original one that has been loaded off the file. This would of course have a
    timing implication but may enable you to get round the problem.

    So you could use:

    2009-11-09 22:23:32 GMT
    Currently I am using JCAM in a manged environment (deployed in WebSphere
    Application Server) and apparently it is not threadsafe.

    JCam processor = new JCam(JCam.Options.VALIDATE,
    (Document)templateDocument.clone, xmlDocument, parameters);
    resultDocument = processor.run(orderType);

    This may help in the short term, but may not fix all the Threading issues.

    If you could raise a BUG against CAMV I will undertake to do some work to make
    sure this works better in that code.

  • jcamnewbie

    jcamnewbie - 2009-11-10

    Ok we tried with the suggested cloning of template. It certainly reduces the
    instances of errors but does not solves the issue.

    For CAMV I have raised a bug for code to be thread-safe. Is it possible to
    make those changes to JCAM as well?

    Also what timelines are we looking for these changes?


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