Re: Obtaining DataContext in ZK

From: Andrus Adamchik (andru..bjectstyle.org)
Date: Wed May 23 2007 - 08:50:57 EDT

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    A note on DC thread-safety. With a few bug fixes that came out in
    2.0.3, DC is fully tread-safe in a read-only situation. In a read/
    write situation DC is still technically thread-safe, but in practice
    at least two types of race conditions can happen:

    * Two or more threads updating the same DataObject (i.e. DataObjects
    are not thread-safe)
    * Two or more threads issuing "commit" or "rollback"

    BTW, I like "one DC per session, one child DC per request" approach
    to solving the problem, but I am yet to try this in a heavily loaded
    read/write app.

    Thanks
    Andrus

    P.S. Should we keep CAY-791 around as a bug, i.e. is there a
    framework-level solution to that, other than better documentation?
    Thoughts?

    On May 23, 2007, at 11:23 AM, Tore Halset wrote:
    > Hello.
    >
    > The DataContext are not thread-safe so you may experience random
    > problems if your app has a single DC used by two different threads.
    >
    > There are different ways to "solve" this issue.
    > A) Make sure each session only have one request at any time. See
    > http://tinyurl.com/2r4kcy
    > B) Use a single DC for each thread. session bound data objects
    > must then be transferred using localObject() between contexts. Or
    > just store the objects ObjectId in the session.
    > C) Use child DC or peer DC. I have not tried this approach.
    >
    > I am sure someone else can come up with other variants.
    >
    > Regards,
    > - Tore.
    >
    > On May 23, 2007, at 03:30, Steve Wells wrote:
    >
    >> I guess the result could be hard to predict and test? Are you
    >> suggesting
    >> that I should wrap the block of dc == null {...} in a synchronized()?
    >>
    >> Clearly my knowledge of this area is limited and I do appreciate your
    >> guidance and questions.
    >>
    >> Steve
    >>
    >> On 23/05/07, Tore Halset <halse..vv.ntnu.no> wrote:
    >>>
    >>> On May 22, 2007, at 05:22, Steve Wells wrote:
    >>>
    >>> > My approach would be to have a simple per session DC and a global
    >>> > web app
    >>> > one...at this stage, hardly seems dangerous, what could
    >>> possibly go
    >>> > wrong?
    >>> > ;)
    >>>
    >>> What if a user (session) issues two simultanous requests?
    >>>
    >>> - Tore.
    >>>
    >
    >

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