[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [sca-j] NEW ISSUE: @Callback injection could be NULL
C Vamsi wrote:
> If a component is providing both bidirectional and non-bidirectional
> services isn't it an error in implementation if a method from
> non-bidirectional service is using a callback?
>
I agree. Getting a NPE doesn't seem to be a bad way to be told
that this programming error has occurred.
> Also, a method from bidirectional service would expect access to a callback
> service and if the callback service is not available, it may not be able to
> serve the request. This situation of NULL callback may not arise when
> bidirectional service is invoked through SCA mechanism, as the interface of
> service and reference will have to match. (One of the situations I see is
> with EJBs providing bidirectional services. What should happen when the EJB
> is invoked as an EJB, not as an SCA service is out of the scope of the
> current discussion I guess.)
>
Skipping over the callback if it wasn't injected (or was injected
as NULL) is unlikely to be the correct thing to do. If the service
implementation needs to invoke this callback because of business
semantics, and the callback wasn't injected, this seems like an
unrecoverable error.
Simon
> ++Vamsi
> Apache Tuscany Committer http://tuscany.apache.org
> Apache Geronimo Committer and Member of PMC http://geronimo.apache.org
>
>
>
> David Booz
> <booz@us.ibm.com>
> To
> 11/02/2009 20:12 sca-j@lists.oasis-open.org
> cc
>
> Subject
> Re: [sca-j] NEW ISSUE: @Callback
> injection could be NULL
>
>
>
>
>
>
>
>
>
>
>
> I'm glad we're doing this in email, and not on the call. We need to do
> more of this.
>
> We need to avoid uninitialized fields and so am asserting that NULL would
> in fact be injected, ensuring that a test for NULL in the app was always
> going to give the correct answer. This makes the two cases parallel (which
> they should be). It doesn't do the app any good to leave uninitialized
> fields laying around.
>
> Good catch on the "should".
>
> I knew about the 76 overlap in the example and chose to ignore it given
> that it hasn't been accepted/applied yet. In any case, I am fine if we
> omit the example updates from the proposal.
>
> This then changes the proposal to:
>
> In section 6.2.4, at the end of the first paragraph (line 395 [1] ) add the
> following:
>
> A field or setter method annotated with @callback is injected or set to
> NULL if the implementation is invoked through a non-bidirectional service
> or when invoked as a callback. It is RECOMMENDED that the component
> implementation checks for null before using a callback reference in this
> situation (See also the getCallbackReference() method in section 8.2
> "RequestContext").
>
>
> Dave Booz
> STSM, BPM and SCA Architecture
> Co-Chair OASIS SCA-Policy TC and SCA-J TC
> "Distributed objects first, then world hunger"
> Poughkeepsie, NY (845)-435-6093 or 8-295-6093
> e-mail:booz@us.ibm.com
>
> (Embedded image moved to file: pic01519.jpg)Simon Nash ---02/10/2009
> 11:18:56 AM---David Booz wrote: > TARGET: Java CAA, section 6.2.4
> "Accessing Callbacks" [1]
>
>
> (Embedde (Embedded image moved to file: pic03501.jpg)
> d image Simon Nash <oasis@cjnash.com>
> moved to
> file:
> pic24194
> .jpg)
> From:
>
> (Embedde (Embedded image moved to file: pic24729.jpg)
> d image sca-j@lists.oasis-open.org
> moved to
> file:
> pic23250
> .jpg)
> To:
>
> (Embedde (Embedded image moved to file: pic28022.jpg)
> d image 02/10/2009 11:18 AM
> moved to
> file:
> pic31249
> .jpg)
> Date:
>
> (Embedde (Embedded image moved to file: pic30621.jpg)
> d image Re: [sca-j] NEW ISSUE: @Callback injection could be NULL
> moved to
> file:
> pic16408
> .jpg)
> Subject:
>
>
>
>
>
>
>
> David Booz wrote:
>> TARGET: Java CAA, section 6.2.4 "Accessing Callbacks" [1]
>>
>> DESCRIPTION: There are situations where the field or setter with an
>> @callback annotation (when used to obtain a reference to a callaback
>> instance) can be injected with NULL. As noted in section 8.2
>> RequestContext, the getCallback() method might return NULL in certain
>> situations, and those situations might also occur in combination with
>> the use of @callback. For example, suppose a component implements two
>> services, one has a bidirectional interface and the other does not. The
>> component impl could use @callback to get a callback instance. When
>> invoked over the bidirectional service, the @callback will non-null, but
>> will be null when the non-bidirectional service is invoked. AFAIK, the
>> specs don't prohibit the example (nor do I think they should).
>>
> This case isn't quite the same as RequestContext.getCallback().
> In that case, the API can return NULL. In this case, the callback
> would not be injected, and so the field would be uninitialized.
>
>> PROPOSAL:
>> There is no pdf for [1] so bear with me:
>> In section 6.2.4, at the end of the first paragraph (line 395) add the
>> following:
>>
>> A field or setter method annotated with @callback might be injected or
>> set to NULL if the implementation is invoked through a non-bidirectional
>> service or when invoked as a callback.
>>
> As I said above, it's not correct to say "...might be injected or
> set to NULL...". It's really "...might not be injected...".
>
>> The component implementation
>> should always check for null before using a callback reference (See also
>>
> You've got a non-RFC2119 "should" here. Even if we found another
> word, I think it's going too far to say that this should *always*
> be done. IMO it should *only* be done if the component logic
> allows this case to arise, which I believe will be a minority of
> all the cases where callbacks are used.
>
>> the getCallbackReference() method in section 8.2 "RequestContext").
>>
>> In section 6.2.4, the first example (line 400) replace the example with
>> the following:
>>
>> @Callback
>> protected ServiceReference<MyCallback> callback;
>>
>> *public void *someMethod() {
>>
>> *if* (callback) {
>> MyCallback myCallback = callback.getCallback(); …
>>
>> myCallback.receiveResult(theResult);
>> }
>> }
>>
> These changes overlap with the proposed changes for JAVA-76,
> and they carry forward one of the problems that is the subject
> of JAVA-76 (incorrectly using getCallback() where getService()
> should be used). Also, bearing in mind my comment above, I'm
> not convinced that this example needs to show the "if". I think
> it's enough to describe the possibility in added text.
>
> Simon
>>
>> [1]
>>
> http://www.oasis-open.org/committees/download.php/31121/sca-javacaa-1.1-spec-cd02-rev2.doc
>> Dave Booz
>> STSM, BPM and SCA Architecture
>> Co-Chair OASIS SCA-Policy TC and SCA-J TC
>> "Distributed objects first, then world hunger"
>> Poughkeepsie, NY (845)-435-6093 or 8-295-6093
>> e-mail:booz@us.ibm.com
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe from this mail list, you must leave the OASIS TC that
> generates this mail. Follow this link to all your TCs in OASIS at:
> https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
>
>
>
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
> ---------------------------------------------------------------------
> To unsubscribe from this mail list, you must leave the OASIS TC that
> generates this mail. Follow this link to all your TCs in OASIS at:
> https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]