Review Request JDK-8200559: Java agents doing instrumentation need a means to define auxiliary classes

[Alan Bateman]

On 02/07/2018 09:41, Rafael Winterhalter wrote:
> Hi,
>
> I was wondering if a solution for this problem is still planned for 
> JDK 11 giving the beginning ramp down.
>
> With removing sun.misc.Unsafe::defineClass, Java agents only have an 
> option to use jdk.internal.misc.Unsafe::defineClass for the use-cases 
> that I described.
>
> I think it would be a missed opportunity not to offer an alternative 
> as of JDK 11 as a second migration would make it even less likely that 
> agents would avoid unsafe API.
>
Mandy's propoal to allow agents doing instrumentation to define 
auxiliary classes in the same runtime package as the class being loaded 
or redefine is a good proposal make complete sense and that fits with 
the intended use of this API. Unfortunately it didn't make JDK 11.

I read the mails and arguments for an Instrumentation.defineClass but I 
don't think it's the right API to add.  The Instrumentation API was 
designed for tool agents, not libraries, and a lot of discussion seems 
to be trying to use the API for cases that it was never intended. Also 
an unrestricted defineClass creates an attractive nuisance that would 
likely create a lot of problems further down the road. I think it would 
be better to focus on some of the use-cases to see if we can identify 
cases where a standard API make sense.

-Alan