Re: [aspectj-users] On generating Aspectj code

[100ji <itz100ji@xxxxxxxxx>]

Andy,

Thanks for a detailed reply.

-S-

On Mon, Jul 21, 2008 at 8:36 PM, Andy Clement <andrew.clement@xxxxxxxxx> wrote:
> Hello,
>
> See comments below...
>
> 2008/7/21 100ji <itz100ji@xxxxxxxxx>:
>> Hi all,
>>
>> I am working on a research project. Boradly, the project is just a
>> fancy logging application that  should log specified fields in
>> specified types at specified point cuts.  All the things that should
>> be specified are fed as an xml file to my python script which performs
>> the following tasks:
>>
>> a) reads an XML file to construct the point cuts
>> b) for each of these point cuts I only need to log some specific data
>> for a specific type from the exposed context. I modify the advice to
>> log those specific parts along with the name of the join point using
>> thisJoinPoint.
>> c) finally all these generated strings are concatenated and written to
>> an aspectj file.
>> d) the generated aspectj file is used to instrument an existing
>> application.
>>
>> I have the following questions: I looked at the ltw-configuration
>> page[1] in the manual, but it didn't seem to answer these questions:
>>
>> generating aspectj files:
>>
>> 1) Is there a better way to generate these aspectj files?
>
> For building AspectJ source files you could try using the Ast
> support to generate aspects but I'm not sure it
> currently supports construction of all the elements of a pointcut
> down to the level you probably like to use.  Or you could generate
> annotated source using the annotation style @Before/@After annotations.
> Of course either of these would still leave with source that needed
> compiling.
> There is no mechanism for direct creation of the bytecode form of
> the aspect.  If you are asking about something to help you build the aop.xml
> files, I don't think there is anything right now.
>
>> 2) I saw that I can specify the point cuts using aop.xml file. But I
>> see that the aop.xml files are generated from the ajc. So, is it a
>> common practice to write aop.xml files? Are there any tutorials on how
>> to write aop.xml files?
>
> The aop.xml files generated by the compiler are just very basic simple
> ones that list the aspects - they are only for use when no further
> customization
> is necessary (eg. further concretization of abstract aspects).
>
> The doc you linked describes everything that can go into an aop.xml file.
>
>> 3) Can I use aop.xml files to perform compile time weaving?
>
> No, see https://bugs.eclipse.org/bugs/show_bug.cgi?id=124460 which
> discusses using aop.xml to control weaving whenever it is done.
>
>> 4) Can I specify advice in aop.xml file?
>
> No, it is just for concretization of abstract pointcuts.
>
>> 5) Also, can someone explain, the concrete and abstract aspects and
>> how all of it related to aop.xml files?
>
> Abstract aspects may contain abstract pointcuts.  Advice attached to
> these abstract pointcuts cannot be applied anywhere until the
> pointcut is fully defined in a concrete sub-aspect.  Because a concrete
> sub-aspect may be trivial, we support defining it directly in XML, within
> aop.xml.  Here is an example, first the abstract:
>
> abstract aspect TraceAspect {
>   abstract pointcut scope();
>   before(): execution(public * *(..)) && scope() {
>     System.out.println("Entering "+thisJoinPoint);
>   }
> }
>
> Now the choices for concrete aspect:
>
> public aspect TracePackageFoo extends TraceAspect {
>   pointcut scope(): within(foo..*);
> }
>
> OR
>
>    <!-- define a concrete aspect inline -->
>    <concrete-aspect name="TracePackageFoo"
>
>      extends="TraceAspect">
>      <pointcut name="scope" expression="within(foo..*)"/>
>    </concrete-aspect>
>
>>
>> building projects:
>>
>> 6) The generated aspectj files, should be applied to random java
>> projects I download from internet. Is load time weaving the best way
>> to apply those aspects? I can't use compile time weaving since it
>> requires messing with the build files of those random java projects
>> which is hard. Can I implement ltw using command line options ( I use
>> makefiles, so this options is important)? What is the general way to
>> do things like this?
>
> I might use binary weaving against the .jars that make up what you have
> downloaded, but loadtime weaving should be OK.  Remember that ltw
> will only weave the code that is exercised in what you run, whilst
> binary weaving will weave everything regardless of whether it is
> exercised in a particular application run.  This can make a difference
> depending on whether you are observing the weaver output messages
> (-showWeaveInfo).
>
> With ltw you have to run something and include the AspectJ java agent,
> so for these random projects you download you will need to have something to
> run
> or you will have to write a driver program that drives the behaviour you
> want to trace.
>
>
>> Performance:
>>
>> 7) During each point cut I need to log the name of the pointcut in the
>> file for which I am using thisJoinPoint. If I  generate a single
>> pointcut and advice for each of the functions I am interested in, will
>> it make my program any faster since thisJoinPoint is slow?
>
> Two kinds of information may be captured in a thisJoinPoint object - static
> fixed information (eg. what method is this, what line am I on) or dynamic
> changing
> information (eg. what are the current parameter values).  If you only use
> the static
>  information then thisJoinPoint is not expensive since it is built once at
> class load
> for the advised locations - but if you use the dynamic information then it
> has to be
> built for every advice call, and that can be expensive.
>
>
> ---
> You don't necessarily need to create the aop.xml directly if you write your
> own
> weaving context for aspectj (implementing IWeavingContext) since then you
> just
> need to give AspectJ what it is expecting (the information that would have
> been
> retrieved from the XML).  However, the documentation on doing this is, errr,
> not
> very good.
>
> From your description of the scenario, I might be tempted to use binary
> weaving.
>
> cheers,
> Andy.
>
>>
>> TIA,
>> -S-
>>
>> [1]
>> http://www.eclipse.org/aspectj/doc/released/devguide/ltw-configuration.html
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