Valhalla EG minutes October 25, 2017

Dan Smith daniel.smith at
Wed Nov 1 23:17:38 UTC 2017

> On Nov 1, 2017, at 9:01 AM, Karen Kinnear <Karen.Kinnear at> wrote:
> 3. Dan S - respond to concerns below

> 1. Issue - why do we have to rename Constant_InvokeDynamic to Constant_DynamicCallSite?
> Remi brought up  a serious concern here
> Summary: there are three levels of impact here:
> 1. JDK tools and JVM implementations
>   e.g. IBM ROM classes today convert back to using constant pool names
> 2. All byte code tools - e.g. ASM, e.g. IDEs, debuggers, profilers
>   a) would need to change to accept either one *** see level 3 for how long this must be supported
>   b) when you print - must choose which one - so you there is not simple “support both”
>        - so user would need to use flags to specify which one they want
>        - goal is to reduce flags, this goes in the wrong direction
> 3. users of byte code tools
>   - e.g. tests - (e.g. IBM and Oracle both raised concerns here)
>   - those who use ASM and other bytecode generation/modification APIs for byte code generation
> *** If the byte code tools do not maintain both names forever, then the level 3: users of byte code tools
> will have to change all their code
> Concern is - this is a significant change for the ecosystem and it does not appear to be justified given a cost/benefit analysis
> — perhaps - this name’s ship has sailed?

I can respond, in the sense that I can provide some thoughts on why this is being proposed and how important it is. If you're looking for someone to weigh the considerations and make a decision, that's not me. :-)

So, some things to consider:

- We can survive without every changing names used as aliases for integer values in JVMS, but over time, especially as we take on some ambitious projects like overhauling the bytecodes, this will accrue into unnecessary complexity/obfuscation.

- It is not strictly necessary for anybody else to use the names in JVMS. But over time the mismatch will accrue into unnecessary complexity/obfuscation on their part. So the decision to change JVMS should be viewed as a commitment to use the new names in tools, etc., after a reasonable amount of time.

- It is good to exercise these "rename a JVM constant" muscles so that they don't atrophy and we find ourselves trapped, unable to ever rename anything.

- This change is not particularly important or urgent, although it makes more sense to change it now with the introduction of CONSTANT_Dynamic than in some arbitrary future release.


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