Re: [aspectj-users] changing pointcut at runtime

[Matthew Webster <matthew_webster@xxxxxxxxxx>]

Wes,

>But you're foraging around a proposal that sounds
interesting: to declare
>programmatically at runtime a concrete aspect using LTW that (only)
>affects the loading of subsequent classes.  In principle this
is doable 
>(at some coherency risk vis-a-vis any classes loaded first), so the
>question becomes whether you can make a compelling use case, particularly
>if it involves a well-defined start/end point for defining subaspects
>programmatically.
This may sound a bit Isaac Asimov but
such a feature would break the first rule of LTW: http://www.eclipse.org/aspectj/doc/released/devguide/ltw-rules.html.
It is very important that a program behave the same regardless of the stage
at which weaving takes place. Allowing an aspect to be defined at an arbitrary
time would most likely result in the scope of weaving being different for
each execution of a program given that, as you point out, this is determined
by the order in which classes are loaded.

>As Eric mentioned, you can advise some join points
and then include a check
>at each one whether to run the advice; you might implement the check
using 
>Pointcut or reflection or what have you.  You cannot change an
existing 
>pointcut, but you can decide what code to run.  (With some cheating
you can
>change the result of an if(..) PCD, but it's clearer to change the
advice.)
The best approach is to weave every eligible join
point shadow with advice associated with an "if()" pointcut filter.
The filter would test at runtime whether a join point was to be advised.
The test can be optimized after the first execution by adding the JoinPoint
to a set. If AspectJ allowed such "runtime" weaving this is probably
the way it would be implemented.

Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM Hursley Park, Winchester,  SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal) 
Email: Matthew Webster/UK/IBM @ IBMGB, matthew_webster@xxxxxxxxxx
http://w3.hursley.ibm.com/~websterm/

"Wes" <wes@xxxxxxxxxxxxxx>
Sent by: aspectj-users-bounces@xxxxxxxxxxx

02/10/2006 07:11

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Subject	Re: [aspectj-users] changing pointcut at runtime

A longstanding and interesting question...

As Eric mentioned, you can advise some join points and then include a check
at each one whether to run the advice; you might implement the check using
Pointcut or reflection or what have you.  You cannot change an existing
pointcut, but you can decide what code to run.  (With some cheating
you can
change the result of an if(..) PCD, but it's clearer to change the advice.)

But you're foraging around a proposal that sounds interesting: to declare
programmatically at runtime a concrete aspect using LTW that (only) 
affects the loading of subsequent classes.  In principle this is doable
(at some coherency risk vis-a-vis any classes loaded first), so the 
question becomes whether you can make a compelling use case, particularly
if it involves a well-defined start/end point for defining subaspects
programmatically.

Wes

> ------------Original Message------------
> From: stalsy <stalsy@xxxxxxxxx>
> To: aspectj-users@xxxxxxxxxxx
> Date: Sun, Oct-1-2006 11:40 AM
> Subject: [aspectj-users] changing pointcut at runtime
>
> 
> Hi all,
> 
> I'm a newbie in aspectj and I need to change a pointcut at runtime
> based on
> the user choice.
> 
> I receive an input String from the user keyboard and I want create
a
> pointcut based on that input. Initially I've thinking at aspect 
> reflection,
> but there isn't any "set" method for this pourpose.
> 
> String comp = InitVars.getFilter(); // get an input from user keyboard
> ....
> AjType dt = AjTypeSystem.getAjType(DynTrace.class); // the aspect
> (DynTrace.aj) in which I would insert new pointcut
> Pointcut pc = dt.getPointcut("filter"); // take the old
pointcut
> PointcutExpression pce = pc.getPointcutExpression(); // take the 
> pointcut
> old _expression_
> 
> now how can I insert new pointcut _expression_( value of variable "comp"
> ) in
> this pointcut? There is another way to make this?
> 
> ES: 
> 
> I get the input "component" from user. Than I would change
the old 
> pointcut 
> public pointcut filter(): Scope() && execution(* *(..));
> to
> public pointcut filter(): Scope() && execution(* component(..));
> 
> where component in pointcut _expression_ is the value of component 
> variable.
> 
> someone can help me, please?
> 
> thank you in advance for replies, best regards
> -- 
> View this message in context: 
> http://www.nabble.com/changing-pointcut-at-runtime-tf2365784.html#a6590719
> Sent from the AspectJ - users mailing list archive at Nabble.com.
> 
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