Classfile API is missing CodeBuilder hook for various instructions-consuming computation tools

[Brian Goetz]

Before we start to do architectural surgery, let's back up a bit and try 
to distill some requirements and goals.  What problems led you here?  
Are these tools we expect people to run full-time, or mostly for 
debugging when something goes wrong?  Can they be applied to ordinary 
classfiles, or do they have to work during building? Could this be 
framed as a kind of transform, instead of a new concept?



On 8/19/2022 2:34 AM, Adam Sotona wrote:
>
> Hi,
>
> I’ve started working on various helper tools that can give user 
> answers during code building.
>
> Answers to questions like:
>
>   * What is actual instructions count
>   * What is actual/max depts of the stack
>   * Which locals have been used
>   * What kinds or exact types are at locals
>   * What kinds or exact types are on stack
>   * Show me a log of all instructions
>   * …
>
> Each of this question has specific use case and calculation of each 
> answer scarifies different amount of resources.
>
> Unfortunately implementation of tool answering any of the above 
> questions requires:
>
> - either heavy use of BufferedCodeBuilder (and complicate existing 
> building or transformation blocks a lot)
>
> - or hacking into CodeBuilder(s) implementation
>
> I would like to propose a similar approach as Linux “tee” tool does, 
> so user can attach another consumer of the CodeElements passed to the 
> CodeBuilder.
>
> It might be just a single method in CodeBuilder:
>
> defaultvoid*tee*(Consumer<CodeElement> secondListener, 
> Consumer<CodeBuilder> handler) {
>
> handler.accept(newTeeCodeBuilder(this, secondListener));
>
>     }
>
> Use case may then look for example like this:
>
> varstackCounter = ...//custom computation tool
> /codeBuilder/./tee/(stackCounter, cb -> {
>             ... //block of instructions to be counted
>         });
>         stackCounter./actual/();
>         stackCounter./max/();
>
> What do you think about this CodeBuilder hook for various 
> instructions-consuming computation tools?
>
> Thanks,
>
> Adam
>
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