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ClockSystem: Embedding Time in Smalltalk
- 1. ClockSystem: Embedding Time in Smalltalk Ciprian Teodorov ENSTA Bretagne, Brest, France
- 2. Overview • Context & MoCvaCons • Logical Time Formalism • ClockSystem: Logical Time in Smalltalk • Example • Conclusion & PerspecCves
- 3. Context & MoCvaCon • Parallel plaGorms available (mulC-‐core, GPU, www) • More and more Parallel & Distributed apps • General-‐purpose languages have constructs for expressing concurrency and exploi+ng parallelism • DifficulCes for reasoning about concurrency: – Low-‐level, implementaCon specific – Lack of formal semanCcs
- 4. Logical Time and Synchronous languages • Logical Time (Leslie Lamport ‘78) – Abstracts “physical” Cme as a par1al order of events – Mul1-‐form, the event need not be Cme related • Enables to describe, manipulate and analyze interacCons, communicaCons, synchronizaCons between processes. • Used in hardware, embedded and distributed systems – Signal, Lustre, Esterel, CCSL
- 5. Clock Constraint SpecificaCon Language (CCSL) • Part of the OMG Marte UML2 profile • Formally expresses Cmed behaviors – RelaCons: precedence, coincidence, exclusion … – Expressions: intersec+on, union, filtering … • Usages: – specifying concurrency semanCcs – expressing Cming requirements
- 6. CCSL primiCves: Examples A = B filtering := always ▼ 001(0110)ω
- 7. ClockSystem Figure 3: Automaton encoding the SDF execution policy • Logical Time embedded in Smalltalk • Automata interpretaCon of CCSL primiCves Figure 4: CLOCKSystem model (abstract syntax)
- 8. for primiCves: StrictPrecedence (<) Figure 5: The infinite automaton of the a b relation ClockSystem Metamodel. At its core, the CLOCKSystem toolkit relies on the Smalltalk implementation of the meta-model presented in Fig. 4. In this meta-model, the two cen-tral concepts are the Clocks and the ClockRelations. The Clocks are instantiated and linked to problem-space ob-jects representing the different events of interests. Each ClockRelations contains an automaton specification en-coding its operational semantics. Conceptually, this automa-ton variable is in transitions value: a set {a}} in should the period clock2 a transition while correct automata-based (such are con-strained CCSL, prece-dence. CLOCKSystem, infi-nite relation-definition In this explicitly the out-going example, the shown by the num-ber state- not passed as arguments when these blocks are evaluated. They can, however, be used in a read-only manner since they will be free variables in the action block and capture their value from the enclosing scope, the automaton block where they are block arguments which are not assignable Smalltalk. Listing 8: The CLOCKSystem definition of the infinite a relation 1 Kernel L ibrar y # s t r i c t P r e c e d e n c e ˆ [ :s :a :b | ” unbounded s t r i c t precedence ” s = 0 i f T r u e : [ { 6 s - ( s + 1) when: {a} } ] i f F a l s e : [ { s - s when: {a . b }. s - ( s + 1) when: {a }. s - ( s - 1) when: {b} } ] ]
- 9. the clock b, which corresponds to our forth synonym Constraints instanCaCon Listing 12: Declaring syntactic synonyms for a b 1 Clock#precedes: ano the rCl ock s e l f system r e l a t i o n : #s t r i c tPr e c edenc e 4 c l o c k s : { s e l f . anotherClock } Clock # ano therClock 7 s e l f precedes: anot h e rCl ock Clock # ano therClock ano therClock precedes: s e l f 10 Clock #follows: ano the rCl ock s e l f ano therClock With these mechanisms in place we consider that has rather succeeded. However, one detail
- 10. Synchronous Data Flow (SDF) Example
- 11. syntactic overhead, again compared to the TimeSquare spec-ification which amounts for almost 100 not included SDF for obvious Constraints: reasons. CCSL lines of code and Listing 4: CCSL specification of the SDF semantics def edge ( clock source , clock t a r g e t , i n t out , i n t i n i t i a l T o k e n s , i n t i n ) clock read clock wr i t e source = (write ▼.(1.0out−1)!) ∧ write read $ initialTokens ∧ (read ▼.(0in−1.1)!) target Listing 5: CLOCKSystem specification of the SDF semantics edgeFrom: sour c e t o : t a r g e t
- 12. source = (write ▼.(1.0out−1)!) ∧ write read $ initialTokens ∧ (read ▼.(0in−1.1)!) target SDF Constraints: ClockSystem Listing 5: CLOCKSystem specification of the SDF semantics edgeFrom: sour c e t o : t a r g e t o u t R a t e : out i n i t i a l : i n i t i a lTo k e n s inRa t e : in |r w| r := self localClock: #read. w := self localClock: #write . sou rce===(w p e r i o d : ({1}, (0 for: (out- 1 ) ) ) ) . w ( r wai tFor : ini t i a lTokens ) . ( r per iod: (0 for : ( in- 1 ) ) , {1}) t a r g e t
- 13. SimulaCon (a) Periodic Trace Automaton A B C (b) Periodic Waveform A B C (c) Trace interpretation (21 steps)
- 15. Passive AcousCc Monitoring ApplicaCon Nodes: 1020 Edges: 4145
- 16. Conclusion • Embedding of Logical Time in Pharo Smalltalk • Extensible automaton-‐based formal kernel • Flexible DSL through message-‐synonyms • Usage Scenarios – Trace interpretaCon – model-‐checking – DSE – tesCng monitoring
- 17. Future Work tesCng monitoring concurrent Smalltalk apps by intercepCng reflecCvely generated events (like var access, method • Support ac+va+ons, etc) for dense-‐Cme representaCon • Mechanisms for dynamically evolving systems • Study the connecCon between ClockSystem constraints and state-‐space decomposiCon in model-‐checking context