Raymond Feng wrote:
Hi,
I added the support for AllowsByReference for the references as well as
the implementation classes/methods based on the spec. Now I have some
questions for the SCA spec (Ideally I should bring these questions to
the SCA spec group but I don't have OASIS membership).
The following is quoted from the SCA spec:
The @AllowsPassByReference annotation allows service method
implementations and client references to be marked as “allows pass by
reference” to indicate that they use input parameters, return values
and exceptions in a manner that allows the SCA runtime to avoid the cost
of copying mutable objects when a remotable service is called locally
within the same JVM.
230 *2.3.4 Using “allows pass by reference” to Optimize Remotable Calls*
231 The SCA runtime MAY use by-reference semantics when passing input
parameters, return values or
232 exceptions on calls to remotable services within the same JVM if
both the service method implementation
233 and the service proxy used by the client are marked “allows pass by
reference”. [JCA20009]
234 The SCA runtime MUST use by-value semantics when passing input
parameters, return values and
235 exceptions on calls to remotable services within the same JVM if the
service method implementation is
236 not marked “allows pass by reference” or the service proxy used by
the client is not marked “allows pass
237 by reference”. [JCA20010]
IIUC, now we need to mark both the reference AND service method
implementation to "AllowsPassByReference" so that the runtime can
optimize the in-vm calls over remotable interfaces using PBR. This seems
to be too restrictive for the following use cases:
1. If the client component implementation knows that for a given
reference, the operations are safe to PBR because the client side
neither modifies the input parameters/return value/exceptions, nor does
it care if the these data are modified by the service side.
>
The "nor does it care" part of that is rather a bold assumption. If the
service retains a reference to a mutable return value after returning
from the method invocation, and modifies the contents of that value
before the client has had a chance to use it (for example, on a
different thread with higher priority), I very much doubt that using
PBR will produce correct results on the client side.
2. If the server component implementation knows that for a given service
method, the operation is safe to PBR because the server side neither
modifies the input parameters/return value/exceptions, nor does it care
if the these data are modified by the client side.
Similarly, if the client modifies the contents of a mutable input
parameter before the service has had a chance to use it (for example,
on a different thread with higher priority), I very much doubt that
using PBR will produce correct results on the service side.
Simon
For case 1 and 2, the PBR can be enabled independently without knowing
the counterpart. Does it make sense for SCA to allow PBR if either
reference OR service method implementation is marked
"AllowsPassByReference"?
Thanks,
Raymond
________________________________________________________________
Raymond Feng
rf...@apache.org <mailto:rf...@apache.org>
Apache Tuscany PMC member and committer: tuscany.apache.org
Co-author of Tuscany SCA In Action book: www.tuscanyinaction.com
Personal Web Site: www.enjoyjava.com
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