On Nov 27, 2006, at 2:58 PM, Raymond Feng wrote:
Hi,
The SCA spec says "Independent of whether the remotable service is
called remotely from outside the process where the service runs or
from another component running in the same process, the data
exchange semantics are by-value."
I plan to add this support. To trigger more discussions, here are
some points to brainstorm.
1) It will apply to a wire with remotable interfaces for the source
and target.
2) We need to take "AllowsPassByReference" into consideration in
the ServiceContract
3) An interceptor will be added to the invocation chain to enforce
the "pass-by-value" semantics by data transformation if necessary
4) How we copy the value depends on the databinding for the given
argument or return value of an operation. A databinding provider
can implement the "copy" method to control how the copy will be made.
We should find a way to not make this necessary in the programming
model except for maybe a few edge cases. This was related to the
discussion a while back about not having to specify the data binding
type as annotations. Like you mention below, in addition to cloning
and serializable (maybe without the need to marshall class
descriptors) we could support XStream for POJOs? I think the end user
experience should be really simple and this copy will hopefully in
90% of the cases transparent. Also, we should probably tell people
that they should use @AllowsByReference in all cases possible since
performance of the copy will introduce significant overhead for
remotable services.
Object copy(Object source, TransformationContext context);
5) For objects without exlicit databinding (in which case, we
assume it's plain java databinding), we'll use techniques:
* Serilization followed by a deserialization (Serialize the data
in source context and deserialize it in target context)
* Cloning? (If the object is Cloneable, can we use the clone()
to make the copy?)
6) Some optimaization can be applied, for example, for immutable
jdk classes such as "java.lang.String" we don't have to make a copy
As one thought, it would be an interesting experiment to see if a
copy-on-write strategy could be done and whether that would improve
or degrade performance. For example, any interface-based parameter
could have a proxy substituted. I'm not sure if this would degrade
performance or make any improvements.
7) For composite services/references with bindings, can we assume
that "pass-by-value" semantics will be automatically enforeced by
the protocol layer for inter-process calls?
I would say yes, we leave this to the binding.
Any thoughts?
Thanks,
Raymond
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