Thanks for the quick response. I agree with the points you are making. A few more arguments:
1) In many cases, the service method produces a DTO and it either doesn't retain a reference to the return value or it won't mutate it after the call. It's not wise to copy the DTO. 2) If the client side modifies the input data in a different thread after issuing a call to the service, the PBV may get the wrong snapshot of the parameters too. 3) For remotable invocations, a typical client sends out a list of DTOs for service invocations, and get a new DTO back. The DTO design usually implies immutable data (even not explicitly enforced in the programming language such as Java). Thanks, Raymond ________________________________________________________________ Raymond Feng 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 ________________________________________________________________ On Feb 7, 2011, at 4:03 PM, Simon Nash wrote: > 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 >> ________________________________________________________________ >
