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JVMLS Notes Day 1

Mirah NLR + yield

Thought I came up w/ talking w/ headius + kotlin dev

Have nonlocal return allowed only for blocks passed to fns that are either: macros, or take a specialized type that's generated from a yield


class A
  def foo
    puts "in ensure"

def bar { return 1 }

and otherwise don't allow returns in blocks. That way it allows ppl to write libs that do NLR, but you have to do it conciously. Not sure if I like it that way, but it's a thought.

Jruby Talk

misuse JVM / things worked around

parsing: CRuby 12k LoC yacc JRuby: Jay parser 4k LoC

Parser problems: parser generates switch statment method that's big enough to need to be split into diff methods. Worked out by enveloping case bodies in tiny classes, several hundred o them.

JRuby uses byte arrays for backing its string impl because ruby & java string semantics radically different.

mixed mode vm running on a mixed mode vm has IR / JIT in JRuby land, but also AST interpreter. Just like JVM :p.

the JITed interpreter is faster than unJITed bytecode equivalent

##interpreter has had at least 4 diff versions

  • original: visitor ast walking
  • big giant switch statement
  • experimental stackless IR
  • current direct exec of AST
  • exec state on artificial stack

##JRuby 9000

  • newIR
  • traditional IR compiler, can do trad compiler opto cuz IR not AST
  • register based
  • CFG, static analysis etc

##JVM tricks / problems manually splitting methods to get around 65k limit lack of class hierarchy analysis bites exceptions + everything being an expression tweaking JIT thingns make you sad unsafe 64bit strie camp byte arrays

##because JRuby strings != Java strings, ##ports ports ports Joni port of oniguruma

  • bytecode engine, shallow callstack
  • interruptable (java's isn't)
  • reforked for nashorn to support char[]


  • char tables, transcoding tables etc
  • faster than JDK for strings

###Fibers CRuby just performs stack swaps JRuby has to use java threads. keeps a pool for this to make creating them not super expensive

ObjectSpace in CRuby walks heap :(, JRuby has impl, but is off by default because it makes things slow.

Nashorn Perf

Bunch of Dudes

JVMLS is good, but no women speaking. It is a small community, but really? Hmmm.

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