Valhalla EG 20200311

[David Simms]

Attendees: Brian, Simms, Fred, John, DanH, Tobi

  - Simms: atomics on EG list...
  - John: ...yeah can stay on list
  - Brian: so we have solved so many problems, that we need to think 
about how to prioritize get the project into spec and implementation...
     - Some library experiments, e.g. comparing Collections experiments 
from model 3 with lworld...we have solved
  - DanH: is this prototype or whiteboard
  - Brian: yeah whiteboard, but we we are confident
  - DanH: conditional methods is this still part of the story ?
  - Brian: may not want them in the same form...right now all the 
reasons we want CM for...aren't there
     - Owe a write up: is we think throwing user visible reif under the 
bus, and letting the VM optimize, give a much more homogeneous 
model...still not a concrete answer...
         - ...but we are up to what do we really need
  - Brian: even if we aggressively specialization, "Erasure pollution"* 
always pops up...
     - Legacy class files
     - Legacy serialized streams
     - Generic methods (compiler doesn't know what to infer)
  - John: so the short is: there is an erased version and specialized 
versions, erased is always permitted (see above)
  -  Brian: yeah, but the VM doesn't have to specialized, it is not 
surfaced in the language
  - John: is there in-determinism there
  - Brian, there is room for failing with runtime exception...list of 
erased to concrete method (just as we have today)
  - John, so there is more or less runtime checking depending on the 
information available
  - DanH: at an allocation site what data are we passing then ?
  - Brian: previous there was a desc for species, what changes here is 
that javac puts bytecode with "new List(TypeParam[int])" but the only 
expects "List" (erased) back
  - DanH: is that type passed through CP or arg...
  - Brian: CP
  - DanH: so new CP types still there
  - Brian: yeah from previous template class discussion, but
     - "Like running with java `-Xerased`"
  - DanH: so reflection for the species gives ?
  - Brian: erased
  - DanH: so a new reif API for reflection
  - Brian: so it fail in some places...so there is question there...
  - DanH: surprised if not gauranteed
  - Brian (those cases with erased above) we can't gaurantee
  - John: That raw types are always a super type
     - There may be an optimization, but be available might not (to user)
  - Brian: if we give tools to make the observation that sharp types are 
available, affects the VM implementation
  - John: maybe, depends on how we pass around this in implementation
  - John: so sort amounts to not having to write "`Foo<**any** T>`"
  - Brian: yeah, with casts / and runtime checks for null etc (lworld 
current)


  - Brian: start warning on primitive wrapping sync...
      - Needs to go in JDK15
  - John: atomic value types might have some common code
      - Let me come up with a webrev with a week
  - John: `java.lang.NonTearable`
      - All: yeah

  - John: so can we dynamically add `IdentityObject` in the VM ?
  - Simms: still a mess, only solves one class of problem
  - John: needs more thought...