Concurrent Functional Programming with Erlang and OTP ( Open Telecom Platform )

1. Concurrent Functional Programming with Erlang and OTP (Open Telecom Platform) Bjarne Däcker <bjarne@erix.ericsson.se>Computer Science Laboratory Ericsson Utvecklings AB Acknowledgements Thomas Arts <thomas@erix.ericsson.se> Hans Nilsson <hans@erix.ericsson.se> Torbjörn Keisu <torbjorn.keisu@ericsson.com> Ulf Wiger <ulf.wiger@ericsson.com>

2. The setting • 1995 PC Week Study of software projects: • 16% successful • 53% operational (but less than successful) • 31% cancelled • Butler Group 1997 on large software projects • 5 out of 6 large projects fail • In >$300M companies, 9 out of 10 large projects fail • How to approach this? • Use high-level modeling tools & generate code? • Raise the level of programming language? • Fight all causes for project failure!

3. Telecom industry Switches, routers, base-stations Networks Mobile telephones

4. Requirements on a Programming Technology for Telecommunication Switching Systems Massive concurrency Soft realtime Distribution Interaction with hardware Very large software systems Complex functionality Continuous operation for many years Software maintenance without stopping the system Stringent quality and reliability requirements Fault tolerance errors

5. History of Erlang No language well suited for telecom systems development 1984: Ericsson Computer Science Lab formed 1998: Open Source Erlang 1991: First fast implementation 1987: Early Erlang Prototype projects 1984-86: Experiments programming POTS with several languages 1996: Open Telecom Platform (research on verification...) 1995: Several new projects 1993: Distributed Erlang

6. Concurrent systems programming languages like Ada, Modula or Chill Functional programming languages like ML or Miranda The Ancestry of Erlang Concurrent functional programming language Erlang

7. Erlang Highlights Functional programming language High abstraction level Pattern matching Concise readable programs • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

8. Definition Implementation -module(ex1). -export([factorial/1]). factorial(0) -> 1; factorial(N) when N >= 1 -> N * factorial(N-1). 1 n*(n-1)! n = 0 n 1 n! = Eshell V5.0.1 (abort with ^G) 1> c(ex1). {ok,ex1} 2> ex1:factorial(6). 720 Erlang Example Basics - Factorial function

9. Eshell V5.0.1 (abort with ^G) 1> c(ex2). {ok,ex2} 2> ex2:qsort([7,5,3,8,1]). [1,3,5,7,8] Erlang Example A few very high-level constructs - QuickSort -module(ex2). -export([qsort/1]). qsort([Head|Tail]) -> First = qsort([X || X <- Tail, X =< Head]), Last = qsort([Y || Y <- Tail, Y > Head]), First ++ [Head|Last]; qsort([]) -> []. "all objects Y taken from the list Tail, where Y > Head"

10. Erlang Highlights Either transparent or explicit concurrency Light-weight processes Highly scalable • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

11. activity(Joe,75,1024) Erlang Example Creating a new process using spawn -module(ex3). -export([activity/3]). activity(Name,Pos,Size) -> ………… Pid = spawn(ex3,activity,[Joe,75,1024])

12. Erlang Example Processes communicate by asynchronous message passing receive {start} -> ……… {stop} -> ……… {data,X,Y} -> ……… end receive {start} -> ……… {stop} -> ……… {data,X,Y} -> ……… end Pid ! {data,12,13}

13. Erlang Example Concurrency - Finite State Machine Selective receive ringing_a(A, B) -> receive {A, on_hook} -> back_to_idle(A, B); {B, answered} -> A ! {stop_tone, ring}, switch ! {connect, A, B}, conversation_a(A, B) after 30000 -> back_to_idle(A, B) end. back_to_idle(A, B) -> A ! {stop_tone, ring}, B ! terminate, idle(A). Asynchronous send Optional timeout

14. Erlang Highlights Response times in the order of milliseconds Per-process garbage collection • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

15. Erlang Highlights Simple and consistent error recovery Supervision hierarchies "Program for the correct case" • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

16. Erlang Example Cooperating processes may be linked together using spawn_link(…,…,…) or link(Pid)

17. Erlang Example When a process terminates, an exit signal is sent to all linked processes … and the termination is propagated

18. Erlang Example Exit signals can be trapped and received as messages receive {‘EXIT’,Pid,...} -> ... end

19. Erlang Example Robust systems can be built by layering “Supervisors” “Workers”

20. Erlang Highlights Explicit or transparent distribution Network-aware runtime system • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

21. Transparent Distribution B ! Msg C ! Msg Erlang Run-Time System Erlang Run-Time System network

22. Simple RPC {rex, Node} ! {self(), {apply, M, F, A}}, receive {rex, Node, What} -> What end {rex, Node} ! {self(), {apply, M, F, A}}, receive {rex, Node, What} -> What end {rex, Node} ! {self(), {apply, M, F, A}}, receive {rex, Node, What} -> What end loop() -> receive {From, {apply, M, F, A}} -> Answer = apply(M, F, A), From ! {rex, node(), Answer} loop(); _Other -> loop() end. loop() -> receive {From, {apply, M, F, A}} -> Answer = apply(M, F, A), From ! {rex, node(), Answer} loop(); _Other -> loop() end. loop() -> receive {From, {apply, M, F, A}} -> Answer = apply(M, F, A), From ! {rex, node(), Answer} loop(); _Other -> loop() end. loop() -> receive {From, {apply, M, F, A}} -> Answer = apply(M, F, A), From ! {rex, node(), Answer} loop(); _Other -> loop() end.

23. Erlang Highlights Easily change code in a running system Enables non-stop operation Simplifies testing • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

24. Erlang Example Version 1 Version 2

25. Erlang Highlights "Ports" to the outside world behave as Erlang processes • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

26. Erlang Example External process Port Port ! {self(), {command, [1,2,3]}}

27. Erlang Example External process Port receive{Port, {data, Info}} ->end

28. Erlang Highlights Erlang runs on any UNIX, Windows, VxWorks, ... Supports heterogeneous networks • Declarative • Concurrency • Soft real-time • Robustness • Distribution • Hot code loading • External interfaces • Portability

29. Systems Overview Applications written in Erlang Applications written in C, C++ or Java OTP Components Standard Libraries Erlang Run-Time System Hardware and Operating System

30. Erlang/OTP • Open Telecom Platform • Middleware for Erlang development • Designed for fault tolerance and portability • Behaviors: A formalization of design patterns • Components • Error handling, reporting and logging • Mnesia, distributed real-time database management system • CORBA • IDL Compiler, Java & C Interface Support • HTTP Server • SNMP Agent • ...

31. OTP Behaviors • "A formalization of design patterns" • A behavior is a framework + generic code to solve a common problem • Each behavior has built-in support fordebugging and software upgrade • Makes it easier to reason about the behavior of a program • Examples of OTP behaviors • application defines how an application is implemented • supervisor used to write fault-tolerant supervision trees • gen_server for writing client-server applications • gen_event for writing event handlers • gen_fsm for finite state machine programming

32. The standard textbook Joe Armstrong, Robert Virding, Claes Wikström and Mike Williams, Concurrent Programming in Erlang, Prentice Hall, 1996,2nd edition, ISBN 0-13-508301-X

33. Interesting web pages Open source Erlang www.erlang.org Commercial Erlang www.erlang.se French Erlang site www.erlang-fr.org

34. Courses/year (10-15 pupils/course)

35. Requests/month to www.erlang.org

36. Downloads/month from www.erlang.org

37. AXD 301: A Telephony-Class, scalable (10-160 GBps) ATM switchdesigned from scratch in less than 3 years • AXD 301 Success factors: • Highly pragmatic, holistic approach • Competent organisation • Efficient process • Excellent technology (e.g. Erlang/OTP) • More than just technology... • Consider all factors together from the start • Erlang was a perfect match for our approach

38. AXD 301 in the marketplace ENGINE: Migrating today's vertical networks into a single multi-service backbone • Central component in Ericsson's ENGINE offering • Several major operators • British Telecom • Vodaphone • Worldcom • Telia • Diveo • ...

39. Briefly about the term Carrier-Class • To us, "Carrier-Class", "Telephony-Class" and"Telecom Profile" are synonymous • The quality we've come to expectfrom public telephony networks • The trend towards multimedia servicesrequires Carrier-Class in more systems • More than just duplication of hardware: • Fault-tolerant software • In-service hardware expansion • In-service software upgrade • Load tolerance • Flexibility (frequent changes + long service life) • Target: 99,999% ("five nines") availability, including planned outages There's no such thing as "almost Carrier-Class"!

40. simple wire-speed logic complex soft-real-time logic ATB ATB ATB ATB Telecom-Class System Architecture Control Processors LineTermination ATM Termination CP IO ATM Mandatory Mated Processor Pair Switch Core CP IO CE FR IO CP Optional Processors Server Device L3F CP IO Clock & Synchronization Device Processor on Each Board

41. Programming languages (control system) • Erlang: ca 1 million lines of code • Nearly all the complex control logic • Operation & Maintenance • Web server and runtime HTML/JavaScript generation • C/C++: ca 500k lines of code • Third party software • Low-level protocol drivers • Device drivers • Java: ca 13k lines of code • Operator GUI applets

42. Experiences from AXD 301 SW Design • Using Erlang in Complex Systems • Fits very well with the incremental design method • High programmer satisfaction • Outstanding support for robustness and concurrency • Very few side-effects  easier to add/change single components • Small directed teams can achieve impressive results • Productivity estimates • Similar line/hour programmer productivity • 4-10 fewer lines of source code (compared to C/C++, Java, PLEX) • 4-10x higher programmer productivity • Similar number of faults per 1000 lines of source code • 4-10x higher quality

43. Functional Requirements • Use cases (in telecom “traffic cases”) • User interfaces • ... • Non-functional Requirements • Code updating without interrupting the service • Distribution over several processors • Automatic handover upon error • Limited restart time • ... • The non-functional requirements are often much trickier to handle and require technology bottom-up rather than analysis top-down.

44. Efficient Program Development Requirements • Interaction with the real environment • Powerful and appropriate abstraction mechanisms • Efficient implementation • Useful tools Ideas Prototyping Productification

45. Erlang {‘home.page’, [{title, “My Home Page”}], [{title, “Welcome to My Home Page”}, {text, [{para, “Sorry, this home page is still under ” “construction. Please come back soon!”} ]} ]}. A Simple Erlang-XML Document XML <?xml version=“1.0”?> <home.page title=“My Home Page”> <title> Welcome to My Home Page </title> <text> <para> Sorry, this home page is still under construction. Please come back soon! </para> </text> </home.page> Almost equivalent

46. Erlang Summary • Declarative • Compact code • Concurrency • Light-weight processes • Message passing • Soft real-time • Robustness • Process supervision • Error trapping • Distribution • Hot code loading • External interfaces • To hardware and other languages • Portability www.erlang.org www.erlang.se

47. The Research Continues ... • HiPE - High Performance Erlang (Uppsala, Astec) • ETOS - Erlang to Scheme (Montréal) • Erlang Verification (SICS, Astec) • Type System (Glasgow) • “Safe” Erlang (Canberra) • Specification Techniques (Aachen) • Erlang Processor (Ericsson CADLab) • ...

48. Erlang User Conference 2000 Hurray !!!

49. Welcome to the next EUC September 27, 2001 Älvsjö. Stockholm www.erlang.se Combined with IFL - International Workshop on the Implementation of Functional Languages September 24-26, 2001 Älvsjö. Stockholm