Erlang, The Road Movie [GOTO:CPH 2011 Keynote]

Erlang, The Road Movie
Lessons learned in Erlang Land

@drkrab
Kresten Krab Thorup
CTO, Trifork
1

About Me
■ Language Geek Emacs/TeX Hacker,
GCC: Objective C, NeXT, Compiled Java,
Ph.D. from Århus [language design]
■ Developer J2EE AppServer,
CORBA/RMI, XA-TM, Java Firefighter
■ Trifork CTO Technology Adoption
Conference Editor, GOTO/QCon

2

’90s Object Revolution

3

Increased
Complexity

4

Increased
Complexity

Program Structure

4

Increased
Complexity

Component Reuse
Program Structure

4

Increased
Complexity

Domain Modeling
Component Reuse
Program Structure

4

Languages

C# Ruby
C++
Smalltalk Java
Simula Objective-C

5

Thinking Tools
Patterns DDD

UML

OOA&D

C# Ruby
C++
Smalltalk Java
Simula Objective-C

6

American Scandinavian
School School
Increased
Complexity

Domain Modeling
Component Reuse
Program Structure

7

School School
Increased Conceptual
Complexity Modeling

Pa rticipatory
Design
Domain Modeling
Component Reuse
Program Structure

7

School School
Economics
Increased Conceptual
Reuse
Complexity Modeling
Engineering
Pa rticipatory
Design
Domain Modeling
Component Reuse
Program Structure

7

School School
Internet
Increased
Complexity

Domain Modeling
Component Reuse
Program Structure

8

Internet
Increased
Complexity

Domain Modeling
Component Reuse
Program Structure

9

More Complexity
Infrastructure made of Software

10

More Complexity

11

More Complexity

12

More Complexity

Fault Tolerance, Availability, QoS

12

More Complexity

Integration, Coordination

12

More Complexity

Cloud, Multi-Core

12

More Complexity We ’re struggling to
n dle these with an
haSoftware
Infrastructure made of
object mindset!

Cloud, Multi-Core

12

Time for a new
revolution?

Cloud, Multi-Core

13

What’s a
Revolution?

Thomas Kuhn
The Structure of Scientific Revolutions
14

paradigm

paradigm

normal
science

15

paradigm
observe
anomalies

paradigm

normal
science

15

paradigm
observe
anomalies

paradigm CRISIS

normal
science

15

paradigm
observe
anomalies

paradigm CRISIS

normal revolutionary
science science

15

paradigm
observe
anomalies normal
science
paradigm CRISIS

normal revolutionary
science science

15

What is the
right paradigm to
cope with these?

Cloud, Multi-Core

16

What is the
right paradigm to
cope with these?

Cloud, Multi-Core
Parallel Compilers
Erlang, Actor Models
Functional, Data-Parallel
16

Johnso n’s blog
Ralph Next J ava” What is the
“Erl ang, the right paradigm to
a very with these?
g to be cope
rlang is goin Its main
... E uage ...
imp orta nt lang erfectly
e is tha t it is p
a Cloud, Multi-Core core, web
dvantag
for the multi-
suite d
Integration, Coordinationt, i t is the
future . In fac
services -QoSd
ck soli
NLY ma ture, ro
Fault Tolerance, Availability,
ble for
O
ge that is suita
lang ua Parallel stems
able sy Compilers
hly scal
ing hig Erlang, Actor iModels
h nes.
writ ore mac
run on multic
to
Functional, Data-Parallel
16

Actors

Objects

American
School
Performance
Engineering
17

Actors

Objects

School School
Performance Conceptual
Engineering Modeling
17

Actors

anomalies

Objects

School School
Performance Conceptual
17

Actors

Quest in this talk:
anomalies

Objects
If Actor-Prog ramming
Paradigm,
is the new Scandinavian
American
School re the
What a anomalies
School
ance uld see Coow? tual
Perform sho
we n ncep
17

Making reliable
distributed control systems
in the presence of errors

19

Making reliable
■ The “secret weapon” for
Ericsson’s market leading,
real-time telephony
systems.

19

Making reliable
■ The “secret weapon” for
Ericsson’s market leading,
real-time telephony
systems.
■ 20+ years of experience
to learn from.

19

Erlang/OTP
Open Telecommunications Platform

■ Embedded
Distributed Systems
■ High Availability
■ In-Production
Upgrades

20

How to Learn Erlang

diss ect a frog,
Don’t
Build One!
Nicolas Negropont
e

21

Your Erlang Program
Platform Framework
BEAM

BEAM Emulator BIFs
Your favorite OS

22

Your Erlang Program
Platform Framework
BEAM

BEAM Emulator BIFs

Your favorite OS

22

Your Erlang Program
Platform Framework
BEAM

ERJANG BIFs
JVM

Java Virtual Machine
Your favorite OS

23

Anomalies in
the object-oriented
world view

24

Figure 2-1 Interface and implementation

interface implementation

11
10
9
8
7
6

25 Looking at such a unit from the inside, as the implem
Graphics from Object-Oriented Programming with Objective C, Apple, 2011

Figure 3-1 An object
Encapsulation

m et h o d

me
et h o d data

thod
m

m et h o d

26

and a data structure that serves
Figure 3-1 An object fields of its data structure are it
hide them from the rest of the
The insight of object-oriented programming is to combine st
m et h o da high-level unit, an object, and to give it language su
data—in Figure 3-1 An object

me
and a data structure that serves those functions. The function

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fields of its data structure are its instanceovariables. The met
hide them from the rest of the program, m et has Figure 3-1 illustrat
d

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Object-oriented programming makes these function groups expl
data
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The only way to an object’s dat
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Object-oriented programming
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really is greater than the sum of itsgroup, rather thanis a componen
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over a specific functional area. It can play a full-fledged modular
If you’ve ever tackled any kind By difficult programmingand be
of combining both state prob
really is greater than the sum o
groups of functions that work on a particular kind of data—im
27 Terminology: Object-oriented terminology varies from language

and a data structure that serves
Figure 3-1 An object fields of its data structure are it
hide them from the rest of the
The insight of object-oriented programming is to combine st
m et h o da high-level unit, an object, and to give it language su
data—in Figure 3-1 An object
ma ly
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and a data structure that serves those functions. The function

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If you’ve ever tackled any kind of difficult programming problem
groups of functions that work on a particular kind of data—implic
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Object-oriented programming makes these function groups expl
data
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group, rather than its components.If you’ve ever tackled any kind
The only way to an object’s dat
m et h o d groups of functions that work o
Object-oriented programming
By combining both state and behavior in a single unit, an object b
really is greater than the sum of itsgroup, rather thanis a componen
parts. An object its kind of se
over a specific functional area. It can play a full-fledged modular
If you’ve ever tackled any kind By difficult programmingand be
of combining both state prob
really is greater than the sum o
groups of functions that work on a particular kind of data—im
27 Terminology: Object-oriented terminology varies from language

and a data structure that serves those functions. The functions are known as the object’s methods, a
fields of its data structure are its instance variables. The methods wrap around the instance variable
hide them from the rest of the program, as Figure 3-1 illustrates.

The insight of object-oriented programming is to 3-1
Figure combineAn object behavior—data The insight of object-oriented programming is to combine
state and and operations on
CHAPTER a high-level unit, an object, and to give it language support. An object is a group of related functions
data—in 3 data—in a high-level unit, an object, and to give it languag
et h o d
and a data structure that serves those functions.m functions are known as the object’s methods, and the serves those functions. The funct
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fields of its data structure are its instance variables. The methods wrap around the instance variables and
fields of its data structure are its instance variables. The m

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The Object Model
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Object-oriented programming makes these function groups explicit and permits you to think in terms
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By combining both state and behavior in a and operations on
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single unit, an Objective-C, which has its either alone; the whole
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Figure C++, Object-oriented terminology varies from lan
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m et h o d in a given period, and data members. This document uses the would need instance variables are kno
are Faucet object
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of whether the tap object terminology of Objective-C, where the water is coming fr
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function groups explicit and
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group, rather than its components. this work, a to an object’s data, the only interface, is through its methods.
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m et h o d of whether the tap
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really is greater than the sum of object can be smarter kind of self-sufficient “subprogram” with jurisdiction
to a mechanical faucet
the program and is able to communicate with other objects. Objects communicate through messages
with a specific functional area. It can attached). But evenmodular role within a larger program design.
over lots of gauges and instruments play a full-fledged to perform methods. systemwith lots of gauges and instruments attached). But even a
a real faucet, like any component, exhibits
are requests
both state and behavior. To effectively model a system, you need programming units, like objects, that also it’s likely that your design has inclu
If you’ve ever tackled any kind of difficult programming problem, To effectively model a system, yo
both state and behavior.
combine state and behavior. groups of functions that work on a particular kind ofstate and behavior.
combine data—implicit “objects” without the language su
Terminology: Object-oriented terminology varies from language to language. For example, in C++, methods and permits you to think in terms
Object-oriented programming makes these function groups explicit
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and a data structure that serves those functions. The functions are known as the object’s methods, a
fields of its data structure are its instance variables. The methods wrap around the instance variable
hide them from the rest of the program, as Figure 3-1 illustrates.

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Figure combineAn object behavior—data The insight of object-oriented programming is to combine
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CHAPTER 3
CHAPTER a high-level unit, an object, and to give it language support. An object is a group of related functions
data—in 3 data—in a high-level unit, an object, and to give it languag
et h o d
and a data structure that serves those functions.m functions are known as the object’s methods, and the serves those functions. The funct
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fields of its data structure are its instance variables. The m

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The Object Model
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and operations on
The Object Model
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data—in a high-level unit, an object, and toreallyit language support.sumobjectparts. An object is a kind of self-sufficient “subprogram” withfunct
give is greater than the An of its is a group of related functions serves those functions. The juris
and a data structure that
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and a data structure that serves those functions. The functions areit’s likelyas the object’s methods,tackled any kind ofinstance programming pr
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fields of ever and the difficult variables. The
over a specific functional area. It can play a full-fledged modular roleare its a larger program designm
within
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fields ofof functions that work its instance variables. data—implicitwrap around the instanceof functions that of theon a particular kind of data—
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the them from the rest
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hide them from the rest of the makes these Figure 3-1 illustrates. Object-oriented of the
Terminology: Object-oriented terminology variesratherlanguage to language.The only way to an objec
group, from than its components. For example, in C++, m
group, rather than its components. The only way to an object’s data, the only interface, is through its methods.
Figure 3-1
are called member functions and instance variables are knownobject members. This document uses
An as data
By combining both state and behavior in a terminology ofobject becomes more than basis in Smalltalk. state and behavior in a single unit, an o
single unit, an Objective-C, which has its either alone; the whole
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really is greater than the sum of its parts. An object is of object-oriented programming is to et h ojurisdictionand behavior—data and operations
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with d
et h o d
over a specific functional area. It can play a full-fledged modular rolean object, and toover a specific functional area. It can play a full-fledged fun
m data—in a high-level unit, within a larger program design. support. An object is a group of related mo
give it language

me
m et h o d
For example, if you were to write a program that The functions are known as the object’s methods, a
and a data structure that serves those functions. modeled home water usage, you might invent obje
me
m et h o d

data

thod
data fields of its data structure are its instance variables. The methods wrap around Faucet object that
represent the various components of the water-delivery system. One might be a the instance variable
thod

Terminology: Object-oriented terminology varies from language and stopprogram, ofTerminology:methods
hide methods to start to language. flow as water, set the rate of
have them from the rest of the the For example, in3-1 illustrates.flow, return the amount of water con
Figure C++, Object-oriented terminology varies from lan
m et h o d
are called member functions and instance variables are known as so on. To do this work, acalled member functions and instance variables to keep
m et h o d in a given period, and data members. This document uses the would need instance variables are kno
are Faucet object
terminology of Objective-C, which has its basis in Smalltalk. is open or shut, how much water is being used, andwhich has its basis in Smalltal
of whether the tap object terminology of Objective-C, where the water is coming fr
Figure 3-1 An
Clearly, a programmatic Faucet object can be smarter than a real one (it’sof difficult programming pr
analogous to a mechanical
For example, if you were to write a program thatm et h o d problem,water usage, you mightexample, if you to anyto write a program that modeled
modeled home it’s likely that your design has includedwere kind
If you’ve ever tackled any kind of difficult programming
If you’ve ever tackled
For invent objects
with lots of gauges and instruments attached). But even a real faucet, like any system component, ex
represent functions that work on a particular kind of data—implicit “objects”be a Faucet language support. work on a particular kind of data—
groups of the various components of the water-delivery system. One might without groups of functions that
represent the various components of the water-delivery sy
the object that would
me
m et h o d

both state and behavior. To effectively model a system, you need programming units, like objects, th
have methods toprogramming makes thesewater, data rate of flow, return the amountthink in terms of theand stop the flow of function the ra
Object-oriented programming makes thesewater, set group
Object-oriented start and stop the flow ofcombine state and behavior. permits you to of methods to start
set the have water consumed
thod

function groups explicit and
in a given period, and so on. To doThe only wayFaucet object would need instance variables toperiod, and so on. To doThe only wayFaucet ob
group, rather than its components. this work, a to an objec
group, rather than its components. this work, a to an object’s data, the only interface, is through its methods.
in a given keep track
of whether the tap is open or shut, how much water is being used,network of interconnected objects that open or shut, how much water part o
A program consists of a and where the watercombining from.is calland behavior in a single unit, an o
of whether the tap
is coming is bei
both state upon each other to solve a
m et h o d
By
By combining both state and behavior in a puzzle unit, an objectin Figure 3-2 (page 16)). Each greater has a the sumrole to play in the overall des
single (as illustrated becomes more than either alone; thethan specific of
object whole
Clearly, a programmatic Faucet its parts. An object is athan a real one (it’s analogous really is a programmatic Faucet its parts. An object is atha
really is greater than the sum of object can be smarter kind of self-sufficient “subprogram” with jurisdiction
Clearly,
to a mechanical faucet object can be smarter kin
the program and is able to communicate with other objects. Objects communicate through messages
over a specific functional area. It can play a full-fledged mo
with a specific functional area. It can attached). But evenmodular role within a larger program design.
over lots of gauges and instruments play a full-fledged to perform methods. systemwith lots of gauges and instruments attached). But even a
a real faucet, like any component, exhibits
are requests
both state and behavior. To effectively model a system, you need programming units, like objects, that also it’s likely that your design has inclu
If you’ve ever tackled any kind of difficult programming problem, To effectively model a system, yo
both state and behavior.
combine state and behavior. groups of functions that work on a particular kind ofstate Object-oriented terminology varies from lan
combine data—implicit “objects” without the language su
Terminology: and behavior.
Terminology: Object-oriented terminology varies from language to language. For example, in C++, methods and permits youvariablesin terms
Object-oriented programming makes these function memberexplicit and instance to think are kno
are called groups functions
28 are called member functions and instance variables are known ascall upon each otherdocument part of the a network interface,basis in Smalltal
data members. This A programuses Objective-C, only ofhas its is through its me
group, rather than its terminology of the of
A program consists of a network of interconnected objects thatcomponents. The onlyto solvean object’s data, the which interconnected object
way to a consists

Active Object +
State Machine Figure 3-1 An object

mailbox
m et h o d

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et h o d
data

thod
m
m et h o d

29

Active Object +
State Machine Figure 3-1 An object

mailbox
m et h o d

me
et h o d
data

thod
m
m et h o d

30

box

empty

full(X)

31

box

empty

{‘put’,X}

full(X)

31

box

empty

{‘put’,X} {‘take’,From} /
send(From, X)

full(X)

31

box() ➞ empty().

empty() ➞ box
receive
{‘put’, X} ➞
full(X)
end. empty

full(X) ➞ {‘put’,X} {‘take’,From} /
send(From, X)
receive
{‘take’, From} ➞ full(X)
From ! X,
empty()
end.

32

box() ➞ empty().

empty() ➞ box
receive
{‘put’, X} ➞
full(X)
end. empty

send(From, X)
receive
From ! X,
empty()
end. {‘peek’,From} /
send(From,{‘ok’, X})

33

box() ➞ empty().

empty() ➞ box
receive
{‘put’, X} ➞
full(X)
end. empty

send(From, X)
receive
From ! X,
empty();
{‘peek’, From} ➞ {‘peek’,From} /
send(From,{‘ok’, X})
From ! {‘ok’, X},
full(X)
end.

34

box() ➞ empty().

empty() ➞
receive
{‘put’, X} ➞
full(X)
end.

full(X) ➞
receive
{‘take’, From} ➞
From ! X,
empty();
{‘peek’, From} ➞
full(X)
end.

35

box() ➞ empty(). Box = spawn(fun box/0),

empty() ➞
receive
{‘put’, X} ➞
full(X)
end.

full(X) ➞
receive
From ! X,
empty();
full(X)
end.

35


empty() ➞ Box ! {‘put’, 27},
receive
{‘put’, X} ➞
full(X)
end.

full(X) ➞
receive
From ! X,
empty();
full(X)
end.

35


empty() ➞ Box ! {‘put’, 27},
receive
{‘put’, X} ➞ Box ! {‘take’, self()},
full(X) receive
end. Value ➞ print(Value)
end
full(X) ➞
receive
From ! X,
empty();
full(X)
end.

35

Interface
Objects
Fixed API

Protocol
Actors API changes
with internal state

36

ma ly
A no Interface
Objects
Fixed API

Protocol
Actors API changes
with internal state

36

But isn’t this expensive?

38

... heard in the ‘90s

Use Objects!

38

... heard in the ‘90s

100.000’s of objects,
Use Objects! are you crazy?

38

... heard yesterday

Use Actors!

38

... heard yesterday

100.000’s of processes,
Use Actors!
silly you!

38

fields of its data structu
hide them from the rest

Effect Containment 3-1
Figure An obje

m et h o d
■ Functional languages

me
et h o d
disallow effects data

thod
■ Many object-oriented

m
m et h o d
styles encourage side
effects.
■ Actors conﬁne effects If you’ve ever tackled an
groups of functions tha
Object-oriented program
39 group, rather than its co

From C++ to Java Garbage Collection

From Java to Erlang State Containment

40

Activity Composition
The Object Model The Object Model

The insight of object-oriented programming is to combine state and behavior—data and operations on
The insight of object-oriented programming is to combine state and
data—in a high-level unit, an object, and to give it language support. An object is a group of related functions give it language support.
data—in a high-level unit, an object, and to
and a data the object’s methods, and the
and a data structure that serves those functions. The functions are known asstructure that serves those functions. The functions are k
fields of its data structure are its instance variables. The methods wrap around the instance variables and variables. The methods w
fields of its data structure are its instance
hide them from the rest of the program, as Figure 3-1 illustrates. hide them from the rest of the program, as Figure 3-1 illustrates.


m et h o d me
spawn m et h o d

me
m et h o d

m et h o d
data data
thod

thod

If you’ve ever tackled any kind of difficult programming problem,If you’ve ever tackled any kind included programming problem, it’
it’s likely that your design has of difficult
groups of functions that work on a particular kind of data—implicit “objects” without the language a particular kind of data—implicit “
groups of functions that work on support.
Object-oriented programming makes these function groups explicit and permits you to think in terms ofthese function groups explicit
Object-oriented programming makes the
group, rather than its components. The only way to an object’s data, the only interface, iscomponents. The only way to an object’s data, th
group, rather than its through its methods.

By combining both state and behavior in a single unit, an object becomes more than eitherand behavior in a single unit, an object bec
By combining both state alone; the whole
really is greater than the sum of its parts. An object is a kind of self-sufficient “subprogram”sum of its parts. An object is a kind of self-s
really is greater than the with jurisdiction
over a specific functional area. It can play a full-fledged modular role within a larger program design. play a full-fledged modular role
over a specific functional area. It can

Terminology: Object-oriented terminology varies from language to language. For example, in C++, methods varies from language to
Terminology: Object-oriented terminology
are called member functions and instance variables are known as data members. Thisfunctions and instance variables are known as da
are called member document uses the
terminology of Objective-C, which has its basis in Smalltalk. terminology of Objective-C, which has its basis in Smalltalk.

For example, if you were to write a program that modeled home water usage, you might invent objects to that modeled home wa
For example, if you were to write a program
represent the various components of the water-delivery system. One mightthe a Faucet object thatof the water-delivery system. On
represent be various components would
have methods to start and stop the flow of water, set the rate of flow, return the amount and stop consumed water, set the rate of flow
have methods to start of water the flow of
41 in a given period, and so on. To do this work, a Faucet object would need instanceand so on.to keep track
in a given period, variables To do this work, a Faucet object woul

Activity Composition
The Object Model The Object Model

The insight of object-oriented programming is to combine state and behavior—data and operations on
The insight of object-oriented programming is to combine state and
data—in a high-level unit, an object, and to give it language support. An object is a group of related functions give it language support.
data—in a high-level unit, an object, and to
and a data the object’s methods, and the
and a data structure that serves those functions. The functions are known asstructure that serves those functions. The functions are k
fields of its data structure are its instance variables. The methods wrap around the instance variables and variables. The methods w
fields of its data structure are its instance
hide them from the rest of the program, as Figure 3-1 illustrates. hide them from the rest of the program, as Figure 3-1 illustrates.


m et h o d me
link m et h o d

me
m et h o d

m et h o d
data data
thod

thod

If you’ve ever tackled any kind of difficult programming problem,If you’ve ever tackled any kind included programming problem, it’
it’s likely that your design has of difficult
groups of functions that work on a particular kind of data—implicit “objects” without the language a particular kind of data—implicit “
groups of functions that work on support.
Object-oriented programming makes these function groups explicit and permits you to think in terms ofthese function groups explicit
Object-oriented programming makes the
group, rather than its components. The only way to an object’s data, the only interface, iscomponents. The only way to an object’s data, th
group, rather than its through its methods.

By combining both state and behavior in a single unit, an object becomes more than eitherand behavior in a single unit, an object bec
By combining both state alone; the whole
really is greater than the sum of its parts. An object is a kind of self-sufficient “subprogram”sum of its parts. An object is a kind of self-s
really is greater than the with jurisdiction
over a specific functional area. It can play a full-fledged modular role within a larger program design. play a full-fledged modular role
over a specific functional area. It can

Terminology: Object-oriented terminology varies from language to language. For example, in C++, methods varies from language to
Terminology: Object-oriented terminology
are called member functions and instance variables are known as data members. Thisfunctions and instance variables are known as da
are called member document uses the
terminology of Objective-C, which has its basis in Smalltalk. terminology of Objective-C, which has its basis in Smalltalk.

For example, if you were to write a program that modeled home water usage, you might invent objects to that modeled home wa
For example, if you were to write a program
represent the various components of the water-delivery system. One mightthe a Faucet object thatof the water-delivery system. On
represent be various components would
have methods to start and stop the flow of water, set the rate of flow, return the amount and stop consumed water, set the rate of flow
have methods to start of water the flow of
42 in a given period, and so on. To do this work, a Faucet object would need instanceand so on.to keep track
in a given period, variables To do this work, a Faucet object woul

Erlang, The Road Movie [GOTO:CPH 2011 Keynote]

Erlang, The Road Movie [GOTO:CPH 2011 Keynote]

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