CoBoxes: Distributed Heaps with Cooperative Tasks

Transcription

1 CoBoxes: Distributed Heaps with Cooperative Tasks Jan Schäfer Arnd Poetzsch-Heffter University of Kaiserslautern HATS WP1 Task 1.1 Meeting June 29th, Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 1 / 23

2 JCoBox Main Features Object-Oriented Class-Based Cooperative tasks Asynchronous method calls Futures Distributed object heaps (CoBoxes) Main Language Mechanism CoBox classes Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 2 / 23

3 JCoBox Main Features Object-Oriented Class-Based Cooperative tasks Asynchronous method calls Futures Distributed object heaps (CoBoxes) Main Language Mechanism CoBox classes Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 2 / 23

4 Why CoBoxes? Unit of Behavior (Runtime Component) Creol: Object JCoBox: CoBoxes (hierarchical object groups) Advantages Complex mutable state (with atomic access) Multiple interface objects Hierarchical structure Abstraction from internal details Internal concurrency Modular semantics for runtime components Active Objects are a special case Sequential OOP is a special case Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 3 / 23

5 Advantages by Example Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 4 / 23

6 Example: org.w3c.dom.document DOM Document Component interface Document { Attr createattribute(string name); Element createelement(string tagname);... } interface Node { Document getownerdocument();... } interface Element extends Node { Attr getattributenode(string name);... } interface Attr extends Node { Element getownerelement();... } Implement as a single active object? Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 5 / 23

7 Example: org.w3c.dom.document (2) :Document :Element :Attr Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 6 / 23

8 Example: org.w3c.dom.document (2) :Document :Element :Attr Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 6 / 23

9 Example: SwitchGroup SwitchGroup - Specification A component which guarentees mutal exclusion for a set of switches, such that only one switch is on and all others are off If a switch in a switch group is turned on all other switches in that group are turned off Switches can only be directly turned on by the client Problem How to guarantee that invariant and allow direct access to switch objects? Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 7 / 23

10 SwitchGroup - With Active Objects - No Direct Access on:true Grp Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

11 SwitchGroup - With Active Objects - No Direct Access on:true turnon(1) Grp Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

12 SwitchGroup - With Active Objects - No Direct Access turnon(1) Grp turnoff() on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

13 SwitchGroup - With Active Objects - No Direct Access turnon(1) Grp turnoff() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

14 SwitchGroup - With Active Objects - No Direct Access turnon(1) Grp turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

15 SwitchGroup - With Active Objects - No Direct Access turnon(1) Grp turnon() on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

16 SwitchGroup - With Active Objects - No Direct Access turnon(1) Grp on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

17 SwitchGroup - With Active Objects - Direct Access Grp on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

18 SwitchGroup - With Active Objects - Direct Access on:true Grp Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

19 SwitchGroup - With Active Objects - Direct Access on:true Grp turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

20 SwitchGroup - With Active Objects - Direct Access on:true Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

21 SwitchGroup - With Active Objects - Direct Access turnoff() on:true Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

22 SwitchGroup - With Active Objects - Direct Access turnoff() Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

23 SwitchGroup - With Active Objects - Direct Access Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

24 SwitchGroup - With Active Objects - Direct Access Grp turnon() on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

25 SwitchGroup - With Active Objects - Direct Access Grp on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

26 SwitchGroup - With CoBoxes on:true Grp Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

27 SwitchGroup - With CoBoxes on:true Grp turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

28 SwitchGroup - With CoBoxes on:true Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

29 SwitchGroup - With CoBoxes turnoff() on:true Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

30 SwitchGroup - With CoBoxes turnoff() Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

31 SwitchGroup - With CoBoxes Grp onreq(this) turnon() Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

32 SwitchGroup - With CoBoxes Grp turnon() on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

33 SwitchGroup - With CoBoxes Grp on:true Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 8 / 23

34 SwitchGroup - With a CoBox Facade Proxy on:true Grp Proxy Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 9 / 23

35 SwitchGroup - Nested CoBoxes Proxy on:true Grp Proxy Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 9 / 23

36 Summary of Advantages Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 10 / 23

37 Complex Mutable State Every non-trivial object has a logical state represented by further objects In Creol represent the whole state as ADT only functional programming inside an object use other active objects to hold state more difficult because of distributed state sequential programming cannot be completely simulated always use: x!m().get problems with reentrancy always use: x!m().await problems with concurrent accesses In JCoBox Sequential OOP within a single CoBox ADTs still useful! Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 11 / 23

38 Sequential OOP within a CoBox Well-known programming technique Easy for programmers Existing tools/knowledge Analysis Verification... Encapsulation of existing legacy code Allows for a smooth migration path Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 12 / 23

39 Multiple Interface Objects Multiple objects as entry points to an object structure Very important for OOP Allows for scalable OO interfaces Examples List: Iterator DOM File System GUI-Frameworks Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 13 / 23

40 Hierarchical Structure Treat groups of CoBoxes semantically as a single unit of behavior Allows for a modular semantics of CoBoxes Does not influence the behavior of individual CoBoxes Like Boxes for sequential OOP Different to published paper version Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 14 / 23

41 Practical Experience Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 15 / 23

42 Practical JCoBox Additional Features Promises (explicitly resolvable futures) Immutable classes Transfer classes Java 5: Generics, annotations,... Plain Java classes Static fields and methods Exceptions Configurable Task Scheduler (very limited) Configurable message ordering guarantees Distribution with RMI Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 16 / 23

43 Implemented Examples FourWins Game with a Swing-GUI Computer player utilizing multiple cores CoCoME Distributed cash desk system Implemented as a product line Classical Examples Philosophers Dating Service... Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 17 / 23

44 Experiences The CoBox model has proven to be useful in practice Deadlocks rarely occur and are easy to find High-Level data-races rarely occur and are easy to find Order guarantee very useful Immutable and Transfer objects are needed ADTs could be used instead Design decisions usually clear Which class should be plain, cobox, transfer, immutable? Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 18 / 23

45 Maude Specification Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 19 / 23

46 Maude Specification Goal: Executable paper rules not optimized for performance Can be used to model-check simple programs Found deadlock in 3-Philosopher example Currently very different to Maude specification of Creol Integration of CoBoxes would be possible, however Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 20 / 23

47 Questions concerning ABS Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 21 / 23

48 Question Concerning Concurrency Model Futures yes, but Promises? Channels? Only ADTs, or also Transfer Objects? Message ordering guarantees? Configurable Scheduling? specified by join patterns? Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 22 / 23

49 General Questions for the ABS (from our perspective) Process-independent data description How to represent object references? Modularity (Notion of a component) Clear behavioral interface description declarative specification language Notion of composition Notion of Refinement Relation to implementation Relation between different models (fully abstract?) Support for features/deltas on the modeling level Well-defined notion concurrency with a pluggable scheduling concept Jan Schäfer CoBoxes WP1 Task 1.1 Meeting 23 / 23