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SCOOP – Eiffel Concurrency

SCOOP – Eiffel Concurrency. Slides adapted from Bertrand Meyer, ETH. Lecture 21: Concurrency and real-time systems. Overview. Goal Basics of the SCOOP model Architecture and implementation of SCOOP Examples Basics of the real-time systems Timing and real-time extensions

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SCOOP – Eiffel Concurrency

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  1. SCOOP – Eiffel Concurrency Slides adapted from Bertrand Meyer, ETH Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM0

  2. Lecture 21: Concurrency and real-time systems Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM1

  3. Overview • Goal • Basics of the SCOOP model • Architecture and implementation of SCOOP • Examples • Basics of the real-time systems • Timing and real-time extensions • Conclusion and future work Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM2

  4. Goal Extend a pure, strongly typed, object-oriented language (Eiffel, …) with • a simple, general and powerful concurrency and distribution model ( SCOOP) • and extend SCOOP to support real-time programming Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM3

  5. The SCOOP model • Simple Concurrent Object-Oriented Programming • High-level concurrency mechanism • Full use of inheritance and other object-oriented techniques • Applicable to many physical setups: multiprocessing, multithreading, distributed execution, etc. Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM4

  6. Object-oriented computation To perform a computation is • to use certain processors • to apply certain actions • to certain objects. Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM5

  7. What makes an application concurrent? Processor:autonomous thread of control supporting sequential execution of instructions on one or more objects Can be implemented as: • Computer CPU • Process • Thread • AppDomain (.NET) … Mapping of processors to computational resources through Concurrency Control File (CCF) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM6

  8. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM7

  9. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM8

  10. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM9

  11. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM10

  12. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM11

  13. Separate feature call (asynchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:separateCLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM12

  14. Feature call (synchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:CLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM13

  15. Separate feature call (asynchronous call) • Fundamental scheme of O-O computation: feature call x.f (a) • x:separateCLASS_X Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM14

  16. Access control policy • Target of a separate call must be formal argument of enclosing routine: store (b:separate BUFFER [G]; value: G)is -- Store value into b. do b.put (value) end • To obtain exclusive access to a separate object, use it as argument of call: my_buffer:separate BUFFER [INTEGER] createmy_buffer store (my_buffer, 10) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM15

  17. From preconditions to wait-conditions Contracts in Eiffel store (b: BUFFER [G]; value: G)is -- Store value into b. require not b.is_full value /= Void do b.put (value) ensure not b.is_empty end ... store (my_buffer, 10) • If b is separate, precondition becomes wait condition (instead of correctness condition) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM16

  18. From preconditions to wait-conditions Contracts in Eiffel store (b:separate BUFFER [G]; value: G)is -- Store value into b. require not b.is_full value /= Void do b.put (value) ensure not b.is_empty end ... store (my_buffer, 10) • If b is separate, precondition becomes wait condition (instead of correctness condition) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM17

  19. Synchronization • No special mechanism needed for client to resynchronize with supplier after separate call. • The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM18

  20. Synchronization • No special mechanism needed for client to resynchronize with supplier after separate call. • The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM19

  21. Synchronization • No special mechanism needed for client to resynchronize with supplier after separate call. • The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query … if value > 10then…end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM20

  22. Synchronization • No special mechanism needed for client to resynchronize with supplier after separate call. • The client will wait only when it needs to: x.f x.g (a) y.f … value := x.some_query … if value > 10then…end • This mechanism is called wait by necessity. Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM21

  23. CCF – Mapping of processors to physical resources • Location of processors need not be specified at compile time • On the fly specification with Concurrency Control File (CCF) creation system "goethe" (4): "c:\prog\appl1\appl1.exe" "beethoven" (2): "c:\prog\appl2\appl2.dll" "Current" (5): "c:\prog\appl3\appl3.dll" end external Database_handler: "daimler_benz" port 9000 ATM_handler: "duerer" port 8001 end default port: 8001; instance: 10 end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM22

  24. CCF – Mapping of processors to physical resources • Location of processors need not be specified at compile time • On the fly specification with Concurrency Control File (CCF) creation system "Current": "c:\prog\appl1\appl1.exe" end end end external Database_handler: "daimler_benz" port 9000 ATM_handler: "duerer" port 8001 end default port: 8001; instance: 10 end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM23

  25. SCOOP platform-independent .NET Compact Framework .NET POSIXThreads … Two-level architecture of SCOOP • SCOOP can be implemented in several environments • Microsoft .NET is our current platform Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM24

  26. Implementation • SCOOPLI for .NET and others • Library implementation of SCOOP in its original version • Uses Remoting and Threading capabilities of .NET • Uses Threading capabilities of the .NET CF on the RTOS Windows CE .NET (and/or other RTOS: VxWorks, etc.) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM25

  27. Example: Bounded buffers separate class BOUNDED_BUFFER [G] inherit BOUNDED_QUEUE[G] end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM26

  28. Example: Bounded buffers indexing description: "Encapsulation of access to bounded buffers" class BUFFER_ACCESS [G] feature put (q: BOUNDED_BUFFER [G]; x: G)is -- Insert x into q, waiting if necessary until there is room. require not q.full do q.put (x) ensure not q.empty end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM27

  29. Example: Bounded buffers remove (q: BOUNDED_BUFFER [G])is -- Remove an element from q, waiting if necessary -- until there is such an element require not q.empty do q.remove ensure not q.full end item (q: BOUNDED_BUFFER [G]): G is -- Oldest element not yet consumed require not q.empty do Result := q.remove end end -- classBUFFER_ACCESS [G] Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM28

  30. Example: Bounded buffers Usage of bounded buffers my_buffer_access: BUFFER_ACCESS [INTEGER] my_bounded_buffer: BOUNDED_BUFFER [INTEGER] createmy_buffer_access createmy_bounded_buffer my_buffer_access.put (my_bounded_buffer, 25) my_buffer_access.put (my_bounded_buffer, 50) my_result := my_buffer_acces.item (my_bounded_buffer) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM29

  31. Example: Dining philosophers separate class PHILOSOPHER inherit GENERAL_PHILOSOPHER PROCESS rename setup as getup undefine getup end feature {BUTLER} step is -- Perform a philosopher’s tasks. do think eat (left, right) end eat (l, r: separate FORK) is -- Eat, having grabbed l and r. do … end end -- class PHILOSOPHER Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM30

  32. Class PROCESS indexing description: "The most general notion of process" deferred classPROCESS feature -- Status report over: BOOLEANis -- Must execution terminate now? deferred end feature -- Basic operations setupis -- Prepare to execute process operations (default: nothing). do end stepis -- Execute basic process operations. deferred end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM31

  33. Class PROCESS (cont.) wrapupis -- Execute termination operations (default: nothing). do end feature -- Process behavior liveis -- Perform process lifecycle. do fromsetupuntiloverloop step end wrapup end end -- classPROCESS Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM32

  34. Class GENERAL_PHILOSOPHER class GENERAL_PHILOSOPHER create make feature-- Initialization make (l, r:separate FORK)is -- Define l as left and r as right forks. do left := l right := r end feature{NONE}-- Implementation left:separate FORK right:separate FORK Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM33

  35. Class GENERAL_PHILOSOPHER (cont.) getup is -- Take any necessary initialization action. do end think is -- Any appropriate action or lack thereof do end end -- class GENERAL_PHILOSOPHER class FORK end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM34

  36. Class BUTLER class BUTLER create make feature count: INTEGER -- The number of both philosophers and forks launch is -- Start a full session. local i: INTEGER do from i := 1 until i > count loop launch_one (participants @ i) i := i + 1 end end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM35

  37. Class BUTLER (cont.) feature --{NONE} launch_one (p: PHILOSOPHER)is -- Let one philosopher start his actual life. do p.live end participants: ARRAY [PHILOSOPHER] cutlery: ARRAY [FORK] feature{NONE}-- Initialization make (n: INTEGER)is -- Initialize a session with n philosophers. require n >= 0 do count := n create participants.make (1, count) create cutlery.make (1, count) make_philosophers launch ensure count = n end Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM36

  38. Class BUTLER (cont.) make_philosophers is -- Set up philosophers. local i: INTEGER p: PHILOSOPHER left, right:separate FORK do from i := 1 until i > count loop left := cutlery @ i right := cutlery @((i \\ count) + 1) create p.make (left, right) participants.put (p, i) i := i + 1 end end invariant count >= 0 participants.count = count cutlery.count = count end-- class BUTLER Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM37

  39. Definition: Real-time system Real-time system (Young, 1982): Any information processing activity or system which has to respond to externally generated input stimuli within a finite and specified period. • The correctness of a real-time system depends not only on the logical result of the computation, but also on the timeat which the results are produced ...  a correct but a late response is as bad as awrong response ... Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM38

  40. Hard and soft real-time systems • Hard real-time Systems where it is absolutely imperative that responses occur within the required deadline. E.g. flight control systems, … • Soft real-time Systems where deadlines are important but which will still function correctly if deadlines are occasionally missed.E.g. data acquisition system, … A single real-time system may have both hard and soft real-time subsystems Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM39

  41. Definition: Embedded system Embedded system: The computer is an information processing component within (embedded in) a larger engineering system. (e.g. washing machine, process control computer, ABS ― Anti Blocking System in vehicles, ...) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM40

  42. Characteristics of real-time systems • Large and complex (up to 20 million lines of code estimated for the Space Station Freedom) • Concurrent control of separate system components • Facilities to interact with special purpose hardware • Extreme reliable and safe • Guaranteed response times Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM41

  43. Components of a real-time system • Hardware (CPU, sensors, ADC, DAC, …) • Real-time OS (e.g VxWorks, QNX, Windows CE .NET, …) • Real-time application and real-time runtime system (e.g. Ada, Real-Time Java, C with Real-Time Posix and hopefully soon Real-Time SCOOP ) Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM42

  44. A simple embedded and real-time example Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM43

  45. A simple embedded and real-time example Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM44

  46. Real-Time Facilities • Notion of time • Clocks • Delays • Timeouts • Temporal scopes Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM45

  47. Notion of time • Linearity: • Transitivity: • Irreflexibility: • Density:  The passage of time is equated with a real line. Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM46

  48. Access to a Clock • Direct access to the environment's time frame(e.g. transmitters for UTC = Universal Time Coordinated, UTC service of GPS) • Using an internal hardware clock that gives an adequate approximation to the passage of time in the environment Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM47

  49. Clocks in Real-Time Java • java.lang.System.currentTimeMillis returns the number of milliseconds since 1/1/1970 GMT and is used by java.util.Date • Real-time Java adds real-time clocks with high resolution time types Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM48

  50. RT Java Time Types (1) public abstract class HighResolutionTime implements java.lang.Comparable { public abstract AbsoluteTime absolute(Clock clock, AbsoluteTime destination); ... public boolean equals(HighResolutionTime time); public final long getMilliseconds(); public final int getNanoseconds(); public void set(HighResolutionTime time); public void set(long millis); public void set(long millis, int nanos); } Slides based on Object Oriented Software Construction 2014-09-23 6:27 PM49

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