Rob Legrand, and Ron K Cytron Washington University in St Louis 1 Brookings Dr Saint Louis, MO

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1 Delvin C. Defoe Rose-Hulman Inst. of Technology 5500 Wabash Ave Terre Haute, IN Rob Legrand, and Ron K Cytron Washington University in St Louis 1 Brookings Dr Saint Louis, MO

2 Research funded by DARPA under contract F C-1697 and The Chancellor's Graduate Fellowship Program at Washington University JTRES 07 in Vienna, Austria. Sept 26 28, 07 2

3 Part I Memory management options Part II Cost analysis for Real-time scopes Part III Connection with RTSJ and pure functional programming Part IV Reclaiming Scopes defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 3

4 Manual or explicit [Kelley & Pohl] Garbage collection (GC) [Collins, McCarthy] Real-time garbage collection [Cheng et al., Bacon et al.] Real-time Specification for Java scoped-memory areas [Bollella et al.] JTRES 07 in Vienna, Austria. Sept 26 28, 07 4

5 Manual or explicit [Kelley & Pohl] Garbage collection (gc) [Collins, McCarthy] Real-time GC [Cheng et al., Bacon et al.] RTSJ scoped memory [Bollella et al.] Semi-manual option Scopes: regions of memory Scopes: limited life times Threads allocate from current scope Predictable allocation Predictable deallocation No dangling pointers JTRES 07 in Vienna, Austria. Sept 26 28, 07 5

6 Manual or explicit [Kelley & Pohl] Garbage collection (gc) [Collins, McCarthy] Real-time GC [Cheng et al., Bacon et al.] ScopedMemory scope = new ScopedMemory(1024); scope.enter(new Runnable() { public void run(){ // do some stuff someobj o = new someobj(); // do some more stuff someobj s = new someobj(); } }); // scope is collected RTSJ scoped memory [Bollella et al.] defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 6

7 Scope E Scope D Scope B Scope C T1 Scope A T2 defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 7

8 Legal Scope D Forbidden Scope B Scope C T1 Scope A T2 defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 8

9 Existing implementations for RTSJ TimeSys [TimeSys Corporation, 2002] jrate [Corsaro et al., 2002] Sun s Java Real-time System No independent cost analysis for scopes defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 9

10 Is a large implementation necessary? Execute it on particular platform Do empirical studies Do we use asymptotic methods? Objective System independent defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 10

queue Scheduling Buffering defoe@rose-hulman.

11 Uses of stack Expression evaluation Syntax parsing Solving search problems Uses of queue Scheduling Buffering JTRES 07 in Vienna, Austria. Sept 26 28, 07 11

12 LIFO ADT PUSH(S, x) POP(S) Top of stack last element All OPS 3 rd element 2 nd element 1 st element defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 12

13 Ops Java RTSJ scopes IS-EMPTY O(1) O(1) PUSH O(1) O(1) POP O(1) O(1) n Ops O(n) O(n) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 13

14 FIFO ADT QUEUE Front Rear DEQUEUE(Q) X 1 X 2 X 3 ENQUEUE(Q, x) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 14

15 QUEUE Front Rear X 1 X 2 X 3 defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 15

16 Ops Java RTSJ scopes ISQ-EMPTY O(1)??? ENQUEUE O(1)??? DEQUEUE O(1)??? n Ops O(n)??? defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 16

17 FRONT vw w Assumption ENQUEUE 1 elmt/scope REAR Queue Scope A Stack defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 17

18 FRONT w v uv w Assumption ENQUEUE 1 elmt/scope REAR Queue Scope A Stack defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 18

19 Ops Java RTSJ scopes ISQ-EMPTY O(1) O(1) ENQUEUE O(1) O(n) DEQUEUE O(1) O(1) n Ops O(n) O(n 2 ) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 19

20 Reduce complexity by doubling # of scopes Need 2*n scopes to store n objects space-time tradeoff Enqueue op that requires new scope takes O(n) time Queue Scope A Stack All other objects enqueued in O(1) time defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 20

21 Ops Java RTSJ scopes ISQ-EMPTY O(1) O(1) ENQUEUE O(1) O(n) DEQUEUE O(1) O(1) n Ops O(n) amortized O(n) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 21

22 New and interesting relationship between the two Mathematical transparency: Named expressions can only ref names strictly older than assigned name Scopes can only ref ancestor scopes JTRES 07 in Vienna, Austria. Sept 26 28, 07 22

23 RTSJ developers migrate implementations from functional languages to RTSJ RTSJ program creates a NHRT Simulate cons cell by creating and entering new scope Populate scope with precisely references for cons cell Runtime analyses follow defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 23

24 RTSJ simulation of pure Lisp program Scopes are exactly sized (cons cell) By construction program is scope-safe Lists and Heaps give good complexity [Okasaki,1996] Scopes never exited Object N Scope N Object 1 C 2 Scope 1 Object 0 C 0 C 1 Scope 0 NHRT defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 24

25 Ops Java RTSJ scopes INSERT O(1) O(1) DELETE-ITEM O(1) O(1) LOOKUP O(n) O(log n) n Ops O(mn) O(m log n) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 25

26 Ops Java RTSJ scopes INSERT O(log n) O(log n) FIND-MIN O(log n) O(log n) DELETE-MIN O(log n) O(log n) n Ops O(m log n) O(m log n) defoe@rose-hulman.edu JTRES 07 in Vienna, Austria. Sept 26 28, 07 26

27 Using the connection scopes are never exited Not reclaimed Use ideas from garage collection Copying garbage collection Reference counting can identify scopes no longer in use Contaminated garbage collection Tree of scopes instead of chain of scopes JTRES 07 in Vienna, Austria. Sept 26 28, 07 27

28 Have shown that there are hidden costs associated with scopes Presented interesting connection between functional program and RTSJ program JTRES 07 in Vienna, Austria. Sept 26 28, 07 28

29 Implement data structure packages in RTSJ that give runtime complexities similar to typical implementations Explore memory management issues associated with data structure implementation JTRES 07 in Vienna, Austria. Sept 26 28, 07 29

30 Questions? JTRES 07 in Vienna, Austria. Sept 26 28, 07 30

Cost Analysis for Real-time Java Scoped-memory Areas

Cost Analysis for Real-time Java Scoped-memory Areas Delvin C. Defoe Rob LeGrand Ron K. Cytron {dcd2, legrand, cytron}@cse.wustl.edu Department of Computer Science and Engineering Washington University