2001-03-19 etx/d/xps-01:002 uen 1 bjarne däcker computer science laboratory ericsson utvecklings ab...

2001-03-19 ETX/D/XPS-01:002 Uen 1

Bjarne Däcker <[email protected]>Computer Science Laboratory

Ericsson Utvecklings AB

Acknowledgements

Thomas Arts <[email protected]>

Hans Nilsson <[email protected]>

Torbjörn Keisu <[email protected]>

Ulf Wiger <[email protected]>

Concurrent Functional Programming with Erlang and OTP (Open Telecom

Platform)

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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!

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Telecom industry

Switches, routers,

base-stations Networks Mobile telephones

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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

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History of Erlang

1984:EricssonComputerScience Labformed

1984-86:ExperimentsprogrammingPOTS with several languages

1998:Open SourceErlang

1987:Early ErlangPrototype projects

1991:First fastimplementation

1993:DistributedErlang

1995:Severalnew projects

1996:Open Telecom Platform(research on verification...)

No language well suitedfor telecom systems

development

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The Ancestry of Erlang

Functional programming languages like ML or

Miranda

Concurrent systems programming languages like Ada, Modula or Chill

Concurrent functional programming language

Erlang

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Erlang Highlights

DeclarativeConcurrencySoft real-timeRobustnessDistributionHot code loadingExternal interfacesPortability

Functional programming languageHigh abstraction level

Pattern matchingConcise readable programs

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Erlang Example

Basics - Factorial function

n! =1

n*(n-1)!

n = 0

n 1

Definition

-module(ex1).-export([factorial/1]).

factorial(0) -> 1;factorial(N) when N >= 1 -> N * factorial(N-1).

Implementation

Eshell V5.0.1 (abort with ^G)1> c(ex1).{ok,ex1}2> ex1:factorial(6).720

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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([]) -> [].

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]

"all objects Y taken from the list Tail,

where Y > Head"

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Erlang Highlights


Either transparent or explicit concurrency

Light-weight processesHighly scalable

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Erlang Example

Creating a new process using spawn

-module(ex3).-export([activity/3]).

activity(Name,Pos,Size) -> …………

Pid = spawn(ex3,activity,[Joe,75,1024]) activity(Joe,75,1024)activity(Joe,75,1024)

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Erlang Example

Processes communicate by asynchronous message passing

Pid ! {data,12,13} receive {start} -> ……… {stop} -> ……… {data,X,Y} -> ………end

receive {start} -> ……… {stop} -> ……… {data,X,Y} -> ………end

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Erlang Example

Concurrency - Finite State Machine

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).

Selective receive

Asynchronous send

Optional timeout

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Erlang Highlights


Response times in theorder of milliseconds

Per-process garbage collection

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Erlang Highlights


Simple and consistenterror recovery

Supervision hierarchies"Program for the correct case"

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Erlang Example

Cooperating processes may be linked together

usingspawn_link(…,…,…)orlink(Pid)

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Erlang Example

When a process terminates, an exit signal is sent to all linked processes

… and the termination is propagated

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Erlang Example

Exit signals can be trapped and received as messages

receive {‘EXIT’,Pid,...} -> ...end

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Erlang Example

Robust systems can be built by layering

“Supervisors”

“Workers”

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Erlang Highlights


Explicit or transparent distributionNetwork-aware runtime system

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Transparent Distribution

Erlang Run-Time SystemErlang Run-Time System Erlang Run-Time SystemErlang Run-Time System

B ! Msg

network

C ! Msg

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Simple RPC

loop() -> receive {From, {apply, M, F, A}} -> Answer = apply(M, F, A), From ! {rex, node(), Answer} loop(); _Other -> loop() end.

{rex, Node} ! {self(), {apply, M, F, A}},receive {rex, Node, What} -> Whatend






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Erlang Highlights


Easily change code in a running system

Enables non-stop operationSimplifies testing

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Erlang Example

Version 1 Version 2

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Erlang Highlights


"Ports" to the outside worldbehave as Erlang processes

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Erlang Example

PortPort Externalprocess

Externalprocess

Port ! {self(), {command, [1,2,3]}}

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Erlang Example

PortPort Externalprocess

Externalprocess

receive {Port, {data, Info}} ->end

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Erlang Highlights


Erlang runs on any UNIX,Windows, VxWorks, ...Supports heterogeneous

networks

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OTP ComponentsOTP Components

Standard LibrariesStandard Libraries

Erlang Run-Time SystemErlang Run-Time System

Hardware and Operating SystemHardware and Operating System

Applications written in Erlang

Applicationswritten in C,C++ or Java

Systems Overview

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Erlang/OTP

Open Telecom PlatformMiddleware for Erlang developmentDesigned for fault tolerance and portabilityBehaviors: A formalization of design patternsComponents

– Error handling, reporting and logging

– Mnesia, distributed real-time database management system

– CORBA

– IDL Compiler, Java & C Interface Support

– HTTP Server

– SNMP Agent

– ...

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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

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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

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Interesting web pagesOpen source Erlangwww.erlang.org

Commercial Erlangwww.erlang.se

French Erlang sitewww.erlang-fr.org

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Courses/year (10-15 pupils/course)

0

5

10

15

20

25

30

35

40

45

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

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Requests/month to www.erlang.org

020000400006000080000

100000120000140000160000180000200000

no

v-98

mar

-99

jul-

99

no

v-99

mar

-00

jul-

00

no

v-00

mar

-01

jul-

01

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Downloads/month from www.erlang.org

0500

1000150020002500n

ov-

98

mar

-99

jul-

99

no

v-99

mar

-00

jul-

00

no

v-00

mar

-01

jul-

01

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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

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ENGINE:Migrating today's vertical networksinto a single multi-service backbone

AXD 301 in the marketplace

Central component in Ericsson's ENGINE offering

Several major operators– British Telecom– Vodaphone– Worldcom– Telia– Diveo– ...

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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 thingas "almost Carrier-Class"!

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Optional Processors

Mandatory Mated Processor Pair

ATM

Control Processors

L3F

CE

Switch

Core

FR

ATB

ATB

ATB

ATB

Server Device

LineTermination

ATM Termination

Clock &Synchronization

Clock &Synchronization

IO

IO

IO

IOCP

CP

CP

CP

Device Processoron Each Board

Telecom-Class System Architecturesimple wire-speed logic complex soft-real-time logic

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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

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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

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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.

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Efficient Program Development

Requirements

Ideas

Prototyping

Productification

Interaction with the real environment

Powerful and appropriate abstraction mechanisms

Efficient implementation

Useful tools

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A Simple Erlang-XML Document

<?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>

XML

{‘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!”}

]}]}.

Erlang

Almost equivalent

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Erlang Summary

Declarative– Compact code

Concurrency– Light-weight processes

– Message passing

Soft real-timeRobustness

– Process supervision

– Error trapping

DistributionHot code loadingExternal interfaces

– To hardware and other languages

Portability

www.erlang.orgwww.erlang.se

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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)

...

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Erlang User Conference 2000

Hurray !!!

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Welcome to the next EUCSeptember 27, 2001

Älvsjö. Stockholm

www.erlang.se

Combined with IFL - International Workshop on the Implementation

of Functional LanguagesSeptember 24-26, 2001

Älvsjö. Stockholm

2001-03-19 etx/d/xps-01:002 uen 1 bjarne däcker computer science laboratory ericsson utvecklings ab...

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