Tapestry 5.2 Leaves the Gate
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It's been a long time coming. Originally, I had thought we'd be producing Tapestry 5.2 six to eight months after Tapestry 5.1 ... instead, it's been more like 14 months just to get to the alpha release. Why? Well, in that time, I've personally changed jobs (back to an independent consultant), and I've been actively using the nightly snapshots of Tapestry 5.2 in two different projects for two different clients. I've had a lot of chances to see Tapestry in practice and, as always, identify the rough edges and smooth them out.
This new release enhances one of Tapestry secret strengths: meta-programming. It is now ridiculously easy to extend the behavior of components, or method or fields within components, using annotations .... without getting mixed up in all that Javassist business. I'm using that now just about everywhere you might think about using a base class: everything from securing page access, to caching, to integration with Google Analytics.
The big change here is the switch from pooled pages to singletons: In Tapestry 5.1 and earlier, Tapestry kept a pool for page instances. On each request, a localized page instance was pulled from the pool, used exclusively by the one request thread, then returned to the pool. The pool had to be able to expand dynamically, and shrink to release memory.
Starting with Tapestry 5.2, the page pool is deprecated (and only enabled with extra configuration). Instead, a single page instance is created and shared between threads. That may raise your red alert flag ... doesn't that make Tapestry non-thread-safe?
Nope. Tapestry now reworks your simple POJO classes, changing access to all local mutable fields to instead store the value in a per-thread Map. It's an extrapolation of how Tapestry already managed persistent fields (storing the persistent field values in the Session between requests) ... but it now applies to all request-scoped state.
It's an interesting trade off: a lot less memory (just a single instance of each page and all its components) for a bit more work during each request. Part of the reason for this alpha release is to get this code into more hands and get more performance analysis on the result. I'm confident that these changes will not noticeably affect small applications and reasonable request loads but will make a big difference in handling larger applications with heavy request loads.
Meanwhile, the goal is to keep the APIs stable, address a bunch of bugs, and get another release out soon, then vote that up as a beta release. Preferably before JavaOne!
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