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Re: Thread safety for components

by Jonathan Locke :: Rate this Message:

I'm not sure precisely what the current synchronization implementation is and there may be some edge cases that are not perfect, but the overall design is single-threaded, meaning you should not need to provide synchronization. Some requests, like image resources would potentially be handled in parallel, but anything that calls user code ought to be synchronized by Wicket so you don't have to think about it. I suppose there might be complications with asynchronous Ajax events, but I would expect these cases are already handled. Is there some specific problem you have run into?

Michael Allan wrote:

I'm trying to get a handle on thread-safety for components. I'm new
to Wicket. My best information, so far, comes from the previous
discussion "Wicket Session and threading":

http://mail-archives.apache.org/mod_mbox/wicket-users/200801.mbox/thread

Eelco Hillenius, in response to Sebastiaan van Erk, wrote:

> Yes. We try our best to make pages/ components as thread safe as
> possible...
>
> > Is there anywhere a small piece on how to deal with threading within
> > Wicket (i.e., what is/is not synchronized in a request/response
> > roundtrip?). I did some quick searching in the mailing list archives and
> > google, but could not find anything related to version 1.3.
>
> Pages are synced on pagemaps, which basically relates to browser
> windows. RequestCycles are separate instances which are not reused, so
> no sync needed there. Sessions are not synced so you need to sync
> manually. Though in practice this wouldn't give much trouble to start
> with. Applications are shared an not synced.

During form processing, however, my own pages are *not* synced on
their pagemaps (at least not on their monitor locks). I placed this
is in my code:

assert Thread.holdsLock( /*page*/this.getPageMap() );

This asserts false during the setting of TextField models (Wicket
1.3.2), and false during the call to Form.onSubmit().

How can I ensure thread safety? In other words, if I am coding a
model, what can I assume about my client threads? Are they
synchronized somewhere, or must I code defensively within the model?
Or, from the client side, if I have a thread that accesses a page's
components, how can it avoid tangling with the response/request
threads?

--
Michael Allan

Toronto, 647-436-4521
http://zelea.com/

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