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From Peter <j...@zeus.net.au>
Subject Re: River-436 - need some explanation of preferred class provider
Date Fri, 07 Mar 2014 18:21:36 GMT
----- Original message -----
> On Mar 7, 2014, at 4:18 AM, Peter <jini@zeus.net.au> wrote:
> > 
> > > Also... Could you elaborate more on code dynamically generated at the
> > > server     and how does it differ from code downloading?
> > 
> > Bytecode for lambda expressions is generated at runtime by the jvm,
> > lambda's use a single serialization proxy class, necessary
> > implementation bytecode is dynamically compiled upon deserialisation.
> > 
> > How lambdas change
> > > anything     (since lambdas are only Java _language_ level constructs I
> > > really don't see     how).
> > 
> > Dynamically compiled code doesn't need a codebase annotation, it's
> > created as needed and it's visibility is correct for each use case,
> > it's very specific, implementing a public interface and interacting
> > through this.
> > 
> Um…are you sure about that?  

Yes, 100%, they're definitely not syntactic sugar, it does serialize the final field arguments
to the lambda expression, so if these are smart proxy's, yes it will need to marshall those
arguments but no, it's not an internal anonymous class and doesn't need to send its enclosing

Go have a look at Brian Goetz's presentations, check out some code and read the development
mail lists, it's pretty cool.



 I confess that I haven’t tried it in code,
> but from reading JSR335, I get the impression that Java lambdas are not
> LISP lambdas, i.e. it’s not so much dynamic byte code generation as
> syntactic sugar that avoids the need to define an interface for what is
> effectively an inner class (it’s not quite an inner class, as it doesn’t
> redefine ‘this’, but is otherwise pretty close.   For example, there
> aren’t real closures; local variables can only be captured if they are
> effectively final).   There also seems to be a lot of compile-time type
> inference going on.   I suspect that passing a lambda as a marshalled
> object will still require the containing class to be loaded.
> Now, dynamic proxies are a different story, and JERI already uses the
> dynamic proxy mechanism.   There’s no need, for example to download an
> implementation class for an object that is directly exported - you only
> really need the service interface to be available locally.   Having said
> that, I think most of us are in the habit of treating “java.rmi.Remote”
> as an implementation detail that shouldn’t be reflected in the service
> interface, so for instance, we’ll have a service interface, “Hello”
> which doesn’t extend Remote, and whose methods may throw IOException,
> and then we’ll have a proxy interface (which goes into the ‘-dl’ or in
> Dennis’ terms ‘-proxy’ jar) called HelloRemote that extends Hello and
> Remote.   The client will download HelloRemote from the codebase
> annotation.
> In any case, I don’t think Java lambdas are the magic bullet you’re
> thinking they are.   I’d be happy to be proven wrong though, because what
> you’re talking about would be pretty cool.   
> Cheers,
> Greg Trasuk

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