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Us M obility R esearch G roup http://mrg.doc.ic.ac.uk/ www.scribble.org Online tool : http://scribble.doc.ic.ac.uk/ End-to-End Switching Programme by DCC End-to-End Switching Programme by DCC Interactions with Industries Interactions with

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http://mrg.doc.ic.ac.uk/

Us ∈ Mobility Research Group

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www.scribble.org

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Online tool : http://scribble.doc.ic.ac.uk/

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End-to-End Switching Programme by DCC

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End-to-End Switching Programme by DCC

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Interactions with Industries

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Interactions with Industries

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Selected Publications 2016/2017

  • [ECOOP’17] Alceste Scala, Raymond Hu, Ornela Darda, NY: A Linear Decomposition of

Multiparty Sessions for Safe Distributed Programming..

  • [COORDINATION’17] Keigo Imai, NY and Shoji Yuen: Session-ocaml: a session-based

library with polarities and lenses.

  • [FoSSaCS’17] Julien Lange , NY: On the Undecidability of Asynchronous Session

Subtyping.

  • [FASE’17] Raymond Hu , NY: Explicit Connection Actions in Multiparty Session Types.
  • [CC’17] Rumyana Neykova , NY: Let It Recover: Multiparty Protocol-Induced Recovery.
  • [POPL’17] Julien Lange , Nicholas Ng , Bernardo Toninho , NY: Fencing off Go: Liveness

and Safety for Channel-based Programming.

  • [FPL’16] Xinyu Niu , Nicholas Ng , Tomofumi Yuki , Shaojun Wang , NY, Wayne Luk :

EURECA Compilation: Automatic Optimisation of Cycle-Reconfigurable Circuits.

  • [ECOOP’16] Alceste Scala, NY: Lightweight Session Programming in Scala
  • [CC’16] Nicholas Ng, NY: Static Deadlock Detection for Concurrent Go by Global

Session Graph Synthesis.

  • [FASE’16] Raymond Hu, NY: Hybrid Session Verification through Endpoint API

Generation.

  • [TACAS’16] Julien Lange, NY: Characteristic Formulae for Session Types.
  • [ESOP’16] Dimitrios Kouzapas, Jorge A. Pérez, NY: On the Relative Expressiveness of

Higher-Order Session Processes.

  • [POPL’16] Dominic Orchard, NY: Effects as sessions, sessions as effects .
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Selected Publications 2016/2017

  • [ECOOP’17] Alceste Scala, Raymond Hu, Ornela Darda, NY :A Linear

Decomposition of Multiparty Sessions for Safe Distributed Programming.

  • [COORDINATION’17] Keigo Imai, NY and Shoji Yuen: Session-ocaml: a session-

based library with polarities and lenses.

  • [FoSSaCS’17] Julien Lange , NY : On the Undecidability of Asynchronous Session

Subtyping.

  • [FASE’17] Raymond Hu , NY : Explicit Connection Actions in Multiparty Session

Types.

  • [CC’17] Rumyana Neykova , NY: Let It Recover: Multiparty Protocol-Induced

Recovery.

  • [POPL’17] Julien Lange , Nicholas Ng , Bernardo Toninho , NY: Fencing off Go:

Liveness and Safety for Channel-based Programming.

  • [FPL’16] Xinyu Niu , Nicholas Ng , Tomofumi Yuki , Shaojun Wang , NY, Wayne Luk:

EURECA Compilation: Automatic Optimisation of Cycle-Reconfigurable Circuits.

  • [ECOOP’16] Alceste Scala, NY: Lightweight Session Programming in Scala
  • [CC’16] Nicholas Ng, NY: Static Deadlock Detection for Concurrent Go by Global

Session Graph Synthesis.

  • [FASE’16] Raymond Hu, NY: Hybrid Session Verification through Endpoint API

Generation.

  • [TACAS’16] Julien Lange, NY: Characteristic Formulae for Session Types.
  • [ESOP’16] Dimitrios Kouzapas, Jorge A. Pérez, NY: On the Relative Expressiveness
  • f Higher-Order Session Processes.
  • [POPL’16] Dominic Orchard, NY: Effects as Sessions, Sessions as Effects.
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Verification framework for Go

Overview Behavioural types SSA IR Go source code

(1) Type inference

(2) Model checking (3) Termina- tion checking

Transform and verify Create input model and formula Pass to termination prover

Check safety and liveness Address type and process gap

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

func main() { ch, done := make(chan int), make(chan int) go send(ch) // Spawn as goroutine. go func() { for i := 0; i < 2; i++ { print("Working...") } }() go recv(ch, done) go recv(ch, done) // Who is ch receiving from? print("Done:", <-done, <-done) // 2 receivers, 2 replies } func send(ch chan int) { ch <- 1 } // Send to channel. func recv(in, out chan int) { out <- <-in } // Fwd in to out.

Send/receive blocks goroutines if channel full/empty resp. Close a channel close(ch) Guarded choice select { case <-ch:; case <-ch2: }

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

Deadlock detection

func main() { ch, done := make(chan int), make(chan int) go send(ch) // Spawn as goroutine. go func() { for i := 0; i < 2; i++ { print("Working...") } }() go recv(ch, done) go recv(ch, done) // Who is ch receiving from? print("Done:", <-done, <-done) // 2 receivers, 2 replies } func send(ch chan int) { ch <- 1 } // Send to channel. func recv(in, out chan int) { out <- <-in } // Fwd in to out.

Run program:

$ go run main.go fatal error: all goroutines are asleep - deadlock!

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

Deadlock detection

func main() { ch, done := make(chan int), make(chan int) go send(ch) // Spawn as goroutine. go func() { for i := 0; ; i++ { // infinite loop print("Working...") } }() go recv(ch, done) go recv(ch, done) // Who is ch receiving from? print("Done:", <-done, <-done) // 2 receivers, 2 replies } func send(ch chan int) { ch <- 1 } // Send to channel. func recv(in, out chan int) { out <- <-in } // Fwd in to out.

Change to infinite

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

Deadlock detection

func main() { ch, done := make(chan int), make(chan int) go send(ch) // Spawn as goroutine. go func() { for i := 0; ; i++ { // infinite loop print("Working...") } }() go recv(ch, done) go recv(ch, done) // Who is ch receiving from? print("Done:", <-done, <-done) // 2 receivers, 2 replies } func send(ch chan int) { ch <- 1 } // Send to channel. func recv(in, out chan int) { out <- <-in } // Fwd in to out.

Change to infinite Deadlock NOT detected (some goroutines are running)

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

Deadlock detection Go has a runtime deadlock detector, panics (crash) if deadlock Deadlock if all goroutines are blocked Some packages (e.g. net for networking) disables it

import _ "net" // Load "net" package func main() { ch := make(chan int) send(ch) print(<-ch) } func send(ch chan int) { ch <- 1 }

Add benign import

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Concurrency in Go

Deadlock detection Go has a runtime deadlock detector, panics (crash) if deadlock Deadlock if all goroutines are blocked Some packages (e.g. net for networking) disables it

import _ "net" // Load "net" package func main() { ch := make(chan int) send(ch) print(<-ch) } func send(ch chan int) { ch <- 1 }

Add benign import Deadlock NOT detected

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I | if e then P else Q

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I | if e then P else Q | newchan(y:σ); P

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I | if e then P else Q | newchan(y:σ); P | P | Q | 0 | (νc)P

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I | if e then P else Q | newchan(y:σ); P | P | Q | 0 | (νc)P | Xh˜ e, ˜ ui D := X(˜ x) = P P := {Di}i∈I in P

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Go Programs as Processes

Go Program

P, Q := π; P π := u!hei | u?(y) | τ | close u; P | select{πi; Pi}i∈I | if e then P else Q | newchan(y:σ); P | P | Q | 0 | (νc)P | Xh˜ e, ˜ ui D := X(˜ x) = P P := {Di}i∈I in P

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Abstracting Go with Behavioural Types

Types

α := u | u | τ T, S := α; T | T S | N{αi; Ti}i∈I | (T | S) | 0 | (new a)T | close u; T | th˜ ui T := {t(˜ yi) = Ti}i∈I in S Types of a CCS-like process calculus Abstracts Go concurrency primitives

Send/Recv, new (channel), parallel composition (spawn) Go-specific: Close channel, Select (guarded choice)

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Verification framework for Go

Model checking with mCRL2 Generate LTS model and formulae from types Finite control (no parallel composition in recursion) Properties (formulae for model checker):

X Global deadlock X Channel safety (no send/close on closed channel) X – Liveness (partial deadlock) X – Eventual reception

Require additional guarantees

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Verification framework for Go

Termination checking with KITTeL Extracted types do not consider data in process Type liveness != program liveness

Especially when involving iteration Check for loop termination

Properties:

X Global deadlock X Channel safety (no send/close on closed channel) X Liveness (partial deadlock) X Eventual reception

func main() { ch := make(chan int) go func() { for i := 0; i < 10; i−− { // Does not terminate } ch <− 1 }() <−ch }

Type: Live Program: NOT live

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Tool demo

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Conclusion

Verification framework based on Behavioural Types Behavioural types for Go concurrency Infer types from Go source code Model check types for safety/liveness + termination for iterative Go code Behavioural types SSA IR Go source code

Type inference

Model checking Termination checking

Transform and verify

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk

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Future work

Extend framework to support more properties Unlimited possibilities!

Different verification techniques

e.g. [POPL’17], Choreography synthesis [CC’15]

Different concurrency issues

Other synchronisation mechanisms Race conditions

Nobuko Yoshida Open Problems of Session Types mrg.doc.ic.ac.uk