Hi David; I thought that if decorator beans are defined with scope @Dependent it seems that no problem occurs regarding thread safety. Because, every time container gets its instance, there will be a new decorator instance.
But at the overall, those concerns are all fine. Thanks; --Gurkan ________________________________ From: David Blevins <[email protected]> To: [email protected] Sent: Fri, October 16, 2009 1:06:10 AM Subject: Decorators and @Decorates injection We don't currently support this and implementing it correctly will actually be tricky. I recommend we ignore everything I'm about to say and just implement it naively for the sake of simplicity and come back and make this change later. The trick: you can't inject the delegate while creating the chain on the fly during a pending invoke. The reason being is a single Decorator instance can apply to several beans and therefore could be executed concurrently. All invocations to those beans will funnel through the same Decorator instance. With Interceptors this is not an issue as the delegate is essentially passed into the around invoke method. With Decorators, it's a field, and overwriting it while it's being accessed by other threads is the definition of not thread-safe. We're essentially going to need to inject a proxy-like object as the delegate and do that once when the Decorator is created. That delegate will have to look in a thread local in some way for the next guy down the chain and send calls to it. That will actually be somewhat of an effort as this is all strongly typed -- we actually need to implement the interface which means well be making one of these for each interface type that can be decorated. This is old-hat in app server land, but will be a bit of an undertaking. Fortunately, one that can be done as an isolated change unrelated to the basic concept of having a stack. We can just do this ignoring thread saftey at first and then get that in there once things look good generally. That's my recommendation anyways. Getting small changes in frequently is usually better than saying "no one touch this code I'm working on it" and have that go on for more than a few days, which is an easy pit to fall into when simple problems continue to get more complicated. Figured I'd mention it up front as the above problem is an easy pit to fall into. -David
