Session Types for Object-Oriented Languages

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1 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 1/1 Session Types for Object-Oriented Languages Dimitris Mostrous joint work with Mariangiola Dezani (Torino), Nobuko Yoshida (Imperial), and Sophia Drossopoulou (Imperial) Monday, 16 October 2006

2 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 2/1 Outline Background Example Syntax and Types Typing System Properties Future Work

3 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 3/1 Introduction A session describes a communication protocol between two parties, that takes place over a single connection Kohei Honda. Types for Dyadic Interaction. CONCUR 93, LNCS 715, pages , Springer-Verlag, 1993

4 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 3/1 Introduction A session describes a communication protocol between two parties, that takes place over a single connection Kohei Honda. Types for Dyadic Interaction. CONCUR 93, LNCS 715, pages , Springer-Verlag, 1993 We integrated sessions in a small object calculus Mariangiola Dezani-Ciancaglini, Dimitris Mostrous, Nobuko Yoshida, and Sophia Drossopoulou. Session Types for Object-Oriented Languages. ECOOP 2006.

5 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 4/1 Protocol Example Scenario: Item Purchasing (Typical W3C example) Exchange of data/objects between three participants (i.e., three processes running in parallel).

6 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 5/1 Session Primitives We chose primitives to: establish connections send and receive values represent conditional flow of protocols represent repetition of part of a protocol allow the transparent delegation of a session

7 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { connect c s { c.send(5); new B.h(); bool x := c.receive;

8 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { connect c s { c is a channel c. send(5); it represents the connection new B.h(); bool x := c.receive; send and receive are the basic primitives for communication

9 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { connect c s { c. send(5); (that we will see next) new B.h(); bool x := c.receive; agree with s s abbreviates a session type the session body must

10 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { c.send(5); new B.h(); bool x := c.receive;

11 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { begin c.send(5); new B.h(); bool x := c.receive;

12 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { begin c.send(5);!int new B.h(); bool x := c.receive;

13 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { begin c.send(5);!int new B.h(); bool x := c. receive;?bool

14 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { begin c.send(5);!int new B.h(); bool x := c. receive;?bool end

15 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { s = connect c s { begin c.send(5);!int new B.h(); bool x := c. receive;?bool end Notation: s = begin.!int.?bool.end

16 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { connect c s { c. send(5); execute? new B.h(); bool x := c.receive; Notation: s = begin.!int.?bool.end when can this connect block

17 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { void m() { connect c s { c. send(5); execute? new B.h(); bool x := c.receive; Notation: s = begin.!int.?bool.end when can this connect block

18 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end suppose we are executing: new C.m(); new D.g();

19 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end communication over the same channel

20 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end session types s and s must agree

21 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end whenever one sends, the other must receive

22 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end types of exchanged data must always be as expected

23 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end s = begin.?int.!bool.end

24 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 6/1 Basics of MOOSE Class C { Class D { void m() { void g() { connect c s { connect c s { c.send(5); //... local computation new B.h(); this.f( c. receive ); bool x := c.receive; c.send(true); Notation: s = begin.!int.?bool.end s = begin.?int.!bool.end s is dual to s (the dual of s is written s )

25 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { c.sendif(x > 5) { int n := c.receive; c.send(true); { c.send(false);... Note: sendif(e) matches with receiveif

26 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.sendif(x > 5) { int n := c.receive; c.send(true); { c.send(false);...

27 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.sendif(x > 5) {! int n := c.receive; c.send(true); { c.send(false);...

28 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.sendif(x > 5) {! int n := c.receive; c.send( true);?int.!bool, { c.send(false);...

29 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.sendif(x > 5) {! int n := c.receive; c.send( true);?int.!bool, { c. send( false);!bool...

30 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.sendif(x > 5) {! int n := c.receive; c.send( true);?int.!bool, { c. send( false);!bool end... Notation: s = begin.!?int.!bool,!bool.end

31 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.receiveif {? c.send( 5); abool := c.receive;!int.?bool, { abool := c.receive;?bool end... Notation: s = begin.?!int.?bool,?bool.end

32 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 7/1 Conditional Sessions... s = connect c s { begin c.receiveif {? c.send( 5); abool := c.receive;!int.?bool, { abool := c.receive;?bool end... Notation: s = begin.?!int.?bool,?bool.end We also have sendwhile(e) and receivewhile for iteration

33 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Methods with Session Parameters connect c1 begin.!bool.!int.end { c1.send(true); c1.send(5); connect c1 begin.?bool.?int.end { c1.receive; c1.receive

34 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Methods with Session Parameters connect c1 begin.!bool.!int.end { c1.send(true); new C.m(c1 ); connect c1 begin.?bool.?int.end { c1.receive; c1.receive

35 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Methods with Session Parameters connect c1 begin.!bool.!int.end { c1.send(true); new C.m(c1 ); connect c1 begin.?bool.?int.end { c1.receive; c1.receive Class C { void m(!int.end x) { x.send(5);

36 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Session over Session connect c1 begin.!bool.!int.end { c1.send(true); c1.send(5); connect c1 begin.?bool.?int.end { c1.receive; c1.receive

37 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Session over Session connect c1 begin.!bool.!int.end { c1.send(true); connect c2 begin.!(!int.end).end { c2.sends( c1 ); connect c1 begin.?bool.?int.end { c1.receive; c1.receive

38 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 8/1 Session over Session connect c1 begin.!bool.!int.end { c1.send(true); connect c2 begin.!(!int.end).end { c2.sends( c1 ); connect c1 begin.?bool.?int.end { c1.receive; c1.receive connect c2 begin.?(!int.end).end { c2.receives(x ) { x.send(5 );

39 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 9/1 Concurrent programming support Class D { void m( x) { spawn {... connect x s {x.send(..).. connect x s {..x.receive;..

40 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 9/1 Concurrent programming support Class D { void m( (s,s) x) { spawn {... connect x s {x.send(..).. connect x s {..x.receive;..

41 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 9/1 Concurrent programming support Class D { void m( (s,s) x) { spawn {... connect x s {x.send(..).. connect x s {..x.receive;.. Most direct way to call it is using newd.m(new (s,s));

42 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 10/1 Syntax of types ::=!? direction π ::= ε π.π t π,π partial session type π (ρ) ρ ::= π.end π. ρ, ρ ended session type s ::= begin.ρ shared session type t ::= C bool s (s,s) standard type

43 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 11/1 Starting a Session...connect c s{e connect c s{e 2..., h

44 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 11/1 Starting a Session...connect c s{e connect c s{e 2..., h...e 1 [c /c]......e 2 [c /c]..., h c c is fresh (i.e., not in the heap h ) we call these live channels

45 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 11/1 Starting a Session...connect c s{e connect c s{e 2..., h...e 1 [c /c]......e 2 [c /c]..., h c c is fresh (i.e., not in the heap h ) we call these live channels recall that c is shared freshness of c guarantees that e 1 and e 2 only interact with each other

46 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 12/1 Interactions...c.send(v)......c.receive..., h

47 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 12/1 Interactions...c.send(v)......c.receive..., h...null......v..., h

48 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 12/1 Interactions...c.send(v)......c.receive..., h...null......v..., h...c.sendif(true ){e 1 {e 2 c.receiveif{e 3 {e 4...,h

49 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 12/1 Interactions...c.send(v)......c.receive..., h...null......v..., h...c.sendif(true ){e 1 {e 2 c.receiveif{e 3 {e 4...,h...e 1 e 3...,h

50 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 13/1 Types for Web Service Example session BuyProduct = begin.!string.?double.!!address.?deliverydetails.end, end Buyer s viewpoint of the Buyer-Seller interaction

51 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 13/1 Types for Web Service Example session RequestDelivery = begin.!productdetails.!(?address.!deliverydetails.end).end Seller s viewpoint of the Seller-Shipper interaction

52 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 13/1 Types for Web Service Example Implementation fits in one A4 page...

53 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t

54 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t standard environment

55 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t expression

56 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t type

57 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t session environment records which channels are used ine, and in what way

58 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t hot set identifies the current/active session channel used to prevent interleaving of sessions

59 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t SEQ Γ;Σ;S e : t Γ;Σ ;S e : t Γ;Σ Σ ;S e;e : t

60 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t Γ;x :?bool;x x.receive:bool Γ;x :!nat;x x.send(5):nat Γ;x :?bool.!nat;x x.receive;x.send(5) : nat

61 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 14/1 Typing Γ;Σ;S e :t We can also infer session types, avoiding type annotations in connect

62 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 15/1 Properties P0 Subject Reduction

63 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 15/1 Properties P0 Subject Reduction P1 no communication error can occur, i.e., there cannot be two sends or two receives on the same channel in parallel in two different threads;

64 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 15/1 Properties P0 Subject Reduction P1 no communication error can occur, i.e., there cannot be two sends or two receives on the same channel in parallel in two different threads; P2 typable threads can always progress unless one of the following situations occurs:

65 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 15/1 Properties P0 Subject Reduction P1 no communication error can occur, i.e., there cannot be two sends or two receives on the same channel in parallel in two different threads; P2 typable threads can always progress unless one of the following situations occurs: a null pointer exception is thrown; there is a connect instruction waiting for the dual connect instruction.

66 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 15/1 Properties P0 Subject Reduction P1 no communication error can occur, i.e., there cannot be two sends or two receives on the same channel in parallel in two different threads; P2 typable threads can always progress unless one of the following situations occurs: a null pointer exception is thrown; there is a connect instruction waiting for the dual connect instruction. P3 after a session has started the required communications are always executed in the expected order.

67 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 16/1 Properties (cont.) P0 Subject Reduction for Threads Γ;Σ P;h and P,h P,h imply Γ ;Σ P ;h with Γ Γ and Σ Σ.

68 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 16/1 Properties (cont.) P0 Subject Reduction for Threads Γ;Σ P;h and P,h P,h imply Γ ;Σ P ;h with Γ Γ and Σ Σ. P2 Progress If P 0, /0 P,h. Then one of the following holds: P,h P,h ; In P, all expressions are values; P throws a null pointer exception; or P stops with a connect waiting for its dual instruction, i.e., P E[connect c s{e] Q.

69 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 17/1 Subject Reduction Proof uses: Generation lemmas; information on how session environments should evolve during reduction; information on the sessions effect of the current redex within larger contexts; the expected difference in sessions effect after reduction; well-definedness conditions on composite environments.

70 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 18/1 Progress Key points: the correspondence of session primitives and session types; information on the current live channel of expressions; knowing the active channel of a thread, we show that some dual expression will appear on a parallel thread, modulo specific exceptions; the two expressions can react, hence we get progress; the non-session cases are more straightforward.

71 Introduction Basics Conditional SoS Meth Operational Semantics Connect Operational Semantics Interactions Typing Properties Future Work p. 19/1 Future Work exception handling and propagation timeout in connect prototype implementation for a longer version with proofs: dm04

Session Types for Object-Oriented Languages

Session Types for Object-Oriented Languages Mariangiola Dezani-Ciancaglini 1, Dimitris Mostrous 2, Nobuko Yoshida 2, and Sophia Drossopoulou 2 1 Dipartimento di Informatica, Università ditorino 2 Department