The document discusses intermediate language design for virtual machines to provide comprehensive concurrency support. It surveys 17 existing virtual machines to evaluate their concurrency support and models. Only 6 provided explicit concurrency support in the intermediate language. Support ranged from low-level instructions to high-level constructs in standard libraries. To enable new concurrency concepts, future virtual machines need intermediate languages that support both low-level and high-level concurrency features, with an open question around the tradeoffs of features in the intermediate language versus the standard library.

1. Intermediate Language Designof High-level Language VMs Towards Comprehensive Concurrency Support Michael Haupt HassoPlattner Institute University of Potsdam Theo D’Hondt Software Languages Lab VrijeUniversiteitBrussel Stefan Marr Software Languages Lab VrijeUniversiteitBrussel VMIL Workshop, 25th October 2009, Orlando, Florida

2. Agenda Motivation Survey Design Concurrency Support Conclusion Outlook 10/27/09 2 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009

3. Motivation VMs support concurrency insufficiently! Why? Because, we want multi-language VMs Fast JITs, great GCs How to design an intermediate language? To our knowledge No surveys No overview of design space/tradeoffs 10/27/09 3 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009

4. Survey Design How to design an intermediate language? 10/27/09 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 4

5. Survey Design 10/27/09 5 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 Dis VM 4th ed. OTP R12 Dalvik VM 1.0 5.1 CLI/ECMA-355 1.3 JVM spec. 1.4 6.0 svn 2.6 Ruby 1.8/1.9 Rubinius V8 svn 4.4 Squeak 3.9 TraceMonkey All trademarks and logos are the property of their respective owners.

6. Survey Criteria Specification vs. implementation Abstraction level of intermediate language Machine model Representation, instruction encoding Instruction categories Arithmetic & logic, control flow, stack, … Optimizations 10/27/09 6 Survey Design

7. Survey 10/27/09 7 Survey Design

8. Survey 10/27/09 8 Survey Design

9. Survey 10/27/09 9 Survey Design

10. Survey 10/27/09 10 Survey Design

11. Survey 10/27/09 11 Survey Design

12. Survey 10/27/09 12 Survey Design

13. Concurrency support How to support concurrency in an intermediate language? 10/27/09 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 13

15. 10/27/09 15 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 Why Concurrency in ILs?

16. Concurrency Support in the IL? 10/27/09 16 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 Dis VM 4th ed. OTP R12 Dalvik VM 1.0 5.1 CLI/ECMA-355 1.3 JVM spec. 1.4 6.0 svn 2.6 Ruby 1.8/1.9 Rubinius V8 svn 4.4 Squeak 3.9 TraceMonkey

17. Concurrency Support in the IL? 10/27/09 17 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009 Dis VM 4th ed. OTP R12 Dalvik VM 1.0 5.1 CLI/ECMA-355 1.3 JVM spec. 1.4 6.0 svn 2.6 Ruby 1.8/1.9 Rubinius V8 svn 4.4 Squeak 3.9 TraceMonkey only 6 out of 17

18. Survey Criteria - Concurrency Concurrency support Concurrency model Included instructions Standard library (stdlib) 10/27/09 18 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009

19. Common Language Infrastructure volatile.(prefix instruction) marks a subsequent pointer reference Synchronized methods Memory model Atomic read or write of certain aligned data Standard library Memory barriers, atomic updates Parallel loops, futures,… 10/27/09 19 Concurrency Support

20. Dis VM (spec. 4th ed.) Inspired by CommunicatingSequentialProcesses spawn – new thread new* – new channel recv, send – on given channel alt, nbalt – send or receive on ready channel Memory model unspecified 10/27/09 20 Concurrency Support

21. Erlang Actors model send, wait, wait_timeout remove_message timeout Pure, functional language No memory model specified Only high-level constructs in stdlib. 10/27/09 21 Concurrency Support

22. Java Virtual Machine monitorenter/-exit For synchronized blocks Synchronized methods Memory model Standard library Low- and high-level constructs DalvikVM promises the same 10/27/09 22 Concurrency Support

23. Mozart LOCKTHREAD No unlock Implicit support Data-flow variables, distribution Standard library High-level constructs Futures, stream channels,… 10/27/09 23 Concurrency Support

24. Conclusion Wide range of supported models No notion of multiple models Often limited to implicit semantics or guaranties Often most functionality in standard library 10/27/09 24 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009

25. Outlook Multi-language VMs have to Enable language designer to invent new constructs/concepts Provide low- and high-level constructs Low-level: Memory barriers, atomic updates, … High-level: Tuplespaces, STM, Actors, … Open question: tradeoffs IL vs. stdlib. 10/27/09 25 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009

26. Discussion 10/27/09 26 IL Design For VMs, Stefan Marr, VMIL, Oct. 2009