Real-Time Programming in Java

Transcription

1 ARTIST2 Summer School 2008 in Europe Autrns (ner Grenole), Frnce Septemer 8-12, Rel-Time Progrmming in Jv Rel-Time in the Age of Complex Systems Invited Speker: Dvid F. Bcon IBM Reserch 0

2 Clssicl Rel-Time Control SENSE COMPUTE ACTUATE Anti-lock Brking System 1

3 Complex Rel-Time Systems 2

4 Wht s Chnging? Processing Power (instructions per 10ms) 1970: 1K Now: 40M 2020: 1G Uiquitous Sensing nd Actution e.g. video strem per cell phone More nd more computing is rel-time 3

5 Implictions for Rel-Time Systems Much Lrger (in code nd scope) Highly Dynmic Non-deterministic non-determinism of underlying system desirle Different Kind of Softwre Engineering 4

6 Memory Mngement STATIC (rrys) Fortrn Esterel Verilog DYNAMIC (mlloc/free) (new/grge collect) C Jv C++ Lisp Ad C# Pscl Smlltlk Determinism Verifiility Flexiility Softwre Engineering 5

7 33% COMMITTED TO PRODUCTION 22% DDG-1000 Destroyer Trde Execution Plysttion/Xox etc 7% Telco SIP Switch RESEARCH TARGETED Automotive Electronics Jv-sed Synthesizer JAvitor (w/ Slzurg) Air Jv (w/ Berkeley CE) 6

8 Three Approches in Jv RTSJ Stndrd: Scoped/Immortl Memory Metronome: Rel-Time Grge Collection Flexotsks: Time-Portle Jv 7

9 Why is Rel-Time Difficult in Jv? No rel-time scheduling APIs Grge Collection Dynmic Clss Loding Just-in-Time (JIT) Compiltion Dynmic, verge-cse-sed optimiztion 8

10 Rel-Time Specifiction for Jv Two primry dditions to the Jv lnguge: Rel-Time Scheduling APIs Semi-mnul memory mngement (rel-time grge collection known impossile) 9

11 Bsic Jv Memory Architecture q s p r X Y T U Stck Stck W Z Hep clss Foo { Foo ; Foo ; } 10

12 RTSJ Memory Architecture C Inner Scope Control Loop Itertion A B D Scope Scope q s Stck p r Stck X W Y Z Hep T U Immortl 11

13 f(,) {.x = ; } Inner Scope Inner Scope Inner Scope Outer Scope Outer Scope Outer Scope Hep Hep Hep 12

14 RTSJ Memory Mngement Issues Complex Progrmming Model Non-compositionl Run-time Filures Checking Overhed Storge Leks in Immortl Memory Often Poorly Suited (e.g. Producer/Consumer) 13

15 Metronome: Rel-Time Grge Collection 14

16 GC: A Simple Prolem (?) p r X Y T U W Z Stck Trnsitive Grph Closure Appliction is Stopped During Collection Memory is only freed t the end 15

17 16 Bsic Approches: Mrk/Sweep Stck r p T X U Z W Y W Z Y X free free O(live) mrk phse ut O(hepsize) sweep Usully requires no copying Mrk stck is O(mxdepth)

18 17 Bsics II: Semi-spce Copying O(live) If single-threded, no mrk stck needed Wstes 50% of memory Stck r p T X U Z W Y W Z Y X

19 Demo: Synthesizer in Jv Humn performnce: Ltency < 8ms end-to-end Jitter < 10us MIDI/soundcrd ltency: 2.5ms 18

20 Kinds of Concurrent Collection Stop the World GC Prllel GC GC GC Concurrent GC Incrementl GC GC GC 19

21 Our Suject: Metronome-2 System GC GC GC GC GC Prllel, Incrementl, nd Concurrent No increment exceeds 450us Rel-time Scheduling Smooth dpttion from under- to over-lod Implementtion in production JVM 20

22 Wht Does Rel-time Men? Miniml, predictle interruption of ppliction Collection finishes efore hep is exhusted Rel spce - ounded, predictle memory Honor thred priorities 21

23 The Cycle of Life Allocte Free Mutte Not relly grge collector ut memory mngement susystem 22

24 Metronome Memory Orgniztion Pge-sed Segregted free lists Rtio ounds internl & pge-internl frgmenttion 23

25 Lrge Ojects: Arrylets (Almost) elimintes externl frgmenttion (Almost) elimintes need for compction Very lrge rrys still need contiguous pges Extr indirection for rry ccess 24

26 Hndling the Concurrency GC Threds Appliction ( muttor ) Threds? Mrk Collect Formt pp rr XX WW YY ZZ TT UU Lod pointer Store pointer Allocte 25

27 Yus Snpshot Algorithm (1990) Logiclly Tke copy-on-write hep snpshot Collect the grge in tht snpshot Physiclly Stop ll threds Copy their stcks ( roots ) Force them to sve over-written pointers Trce roots nd over-written pointers 26 * Dijktstr 75, Steele 76

28 1: Tke Logicl Snpshot p r X Y T U W Z Stck 27

29 2(): Copy Over-written Pointers p r X Y T U W Z Stck 28

30 2(): Trce p X Y T U Stck W Z * Color is per-oject mrk it 29

31 2(c): Allocte Blck p X Y T U s Stck V W Z 30

32 3(): Sweep Grge free p X Y T U s Stck V W Z 31

33 3(): Allocte White free p t s Stck V2 V X W Y Z T U 32

34 33 4: Cler Mrks Stck p T X U Z Y Z Y X s V free free V2 V2 t V W W

35 Yus Algorithm Phses Snpshot stck nd glol roots Trce Flip Sweep Flip Cler Mrks 34 * Synchronous

36 Metronome-2 Concurrency GC Mster Thred GC Worker Threds Appliction Threds (my do GC work) 35

37 Metronome-2 Phses Initition Setup turn doule rrier on Root Scn Active Finlizer scn Clss scn Thred scn** switch to single rrier, color to lck Deugger, JNI, Clss Loder scn Trce Trce* Trce Terminte*** Re-mteriliztion 1 Wek/Soft/Phntom Reference List Trnsfer Wek Reference clering** (snpshot) Re-Trce 1 Trce Mster (Trce*) (Trce Terminte***) Re-mteriliztion 2 Finlizle Processing Clering Monitor Tle clering JNI Wek Glol clering Deugger Reference clering JVMTI Tle clering Phntom Reference clering Re-Trce 2 Trce Mster (Trce*) (Trce Terminte***) Clss Unloding Flip Move Aville Lists to Full List* (contention) turn write rrier off Flush Per-thred Alloction Pges** switch lloction color to white switch to temp full list Sweeping Sweep* Switch to regulr Full List** Move Temp Full List to regulr Full List* (contention) Completion Finlizer Wkeup Clss Unloding Flush Clerle Compction** Book-keeping * Prllel ** Cllck *** Single ctor symmetric 36

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