1. Industrial Use of a Functional Language
Thomas Arts
Industrial Use of a Functional Language
Thomas Arts
Ericsson
Computer Science Laboratory
Stockholm, Sweden

2. Switches, routers, base-stations Networks Mobile telephones
Thomas Arts
Telecom industry
Switches, routers,
base-stations
Networks
Mobile telephones

3. Computer Science Laboratory
Thomas Arts
Computer Science Laboratory
Founded 1983
Research on implementation tools, methods and techniques for telecommunication applications
Intermediate between universities and Ericsson product units

4. Telecom requirements Requirements of telecom software Concurrency
Thomas Arts
Telecom requirements
Requirements of telecom software
Concurrency
Distribution
Soft real-time
Robust
Non-stop system
External interfaces

5. Thomas Arts
A good language?
Experiments in the 80s with Ada, C, ML, CML, Prolog...
large programs (million lines)
change code in running system
fast message passing
low memory overhead
no memory fragmentation/leaks
recover from errors

6. Thomas Arts
Erlang/OTP
A functional language successfully used for programming large real-time control systems.
OTP is the set of libraries that is used with Erlang for product development

7. Erlang/OTP www.erlang.org Erlang/OTP develop/maintenance
Thomas Arts
Erlang/OTP
Erlang/OTP develop/maintenance
Erlang consultancy & courses
Erlang used many systems, e.g. ATM switch and new GSM network (GPRS)
Erlang Open Source

8. Erlang sequential program
Thomas Arts
Erlang sequential program
-module(math).
-export([fac/1]).
fac(N) when N>0 ->
N*fac(N-1);
fac(N)-> 1.

9. Erlang datatypes atoms (true,foo,’Hello’) numbers (1212864187154)
Thomas Arts
Erlang datatypes
atoms (true,foo,’Hello’)
numbers ( )
floats ( )
tuples ({a,123})
lists ([1,123,2,56])
process identifiers
...

10. dynamically typed language poor mechanism to build your own datatypes
Thomas Arts
Erlang datatypes
dynamically typed language
poor mechanism to build your own datatypes

11. Erlang control structures
Thomas Arts
Erlang control structures
Matching
case X of
{ok,List} -> hd(List);
{resend,Data} -> submit;
error -> exit(error);
_ -> retry(X)
end

12. Erlang control structures
Thomas Arts
Erlang control structures
Guards
f(....) when guard -> ... If
f(X) ->
if guard1 -> ...;
guard2 -> ...
end

13. Erlang control structures
Thomas Arts
Erlang control structures
Higher order functions
f(F,X) -> F(X);
map(F,[1,2,3,4]).
List comprehensions
[ X || {X,Y}<-Set, guard(X)]

14. Erlang control structures
Thomas Arts
Erlang control structures
Naming of objects/data
f(X) ->
Dev = update_device(X),
{Date,Time} = now(),
h({Dev,Date}).

15. Erlang control structures
Thomas Arts
Erlang control structures
Sequence
f(X) ->
action1(X),
action2(X);
update(X) ->
log(X,”myfile”), new(X).
side-effects

16. Erlang control - concurrency/distribution
Thomas Arts
Erlang control - concurrency/distribution
Creating a process
Pid = spawn(F,[Arg1,...,ArgN]);
B = spawn(F,Args); P2 P1 P2
F(Arg1,...,ArgN)

17. Erlang control - concurrency/distribution
Thomas Arts
Erlang control - concurrency/distribution
Sending messages
Pid ! Message;
B!{self(),hej};
{P1,hej} P1 P2
{P1,hej}

18. Erlang control - concurrency/distribution
Thomas Arts
Erlang control - concurrency/distribution
Receiving messages
receive
Pattern -> ...;
end;
Distrubution has same communication mechanism
Hence, concurrency or distribution is transparant for user P1 P2
{P1,hej}
receive
{From,Msg} ->
From ! {ok,Msg}
end
P1 ! {ok,hej}

19. Erlang changing code in running system
Thomas Arts
Erlang changing code in running system P0
loop(F) ->
receive
{change,G} ->
loop(G);
{exec,Pid,Arg} ->
Pid!F(Arg),
loop(F)
end;
loop(F) ->
receive
{exec,Pid,Arg} ->
Pid!F(Arg),
loop(F)
end;
Distrubution has same communication mechanism
Hence, concurrency or distribution is transparant for user P1
P0 ! {exec,self(),15},
N = receive
Answer ->
Answer
end,
N = F(15),

20. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
Processes can be linked to each other:
PidA
PidB
Links are created by using either:
link(Pid), or
spawn_link(Module, Function, Args)
Links are bi-directional.
They can be removed using unlink(Pid).

21. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
When a process terminates, an exit signal is sent to all processes the process is linked to:
PidA
PidA
PidB
A process can terminate normally, due to a run-time error, or when explicitly ordered to do so.

22. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
If a process terminates abnormally, the emitted exit signal will (by default) cause the recipient to terminate:
The termination reason in the transmitted exit signals will be the same as in the received one (the exit signal is propagated).
PidA
PidB
PidB
PidC
PidD
PidD
PidE

23. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
A process can terminate itself using exit(Reason). This will cause exit signals with termination reason Reason to be emitted.
exit(error)
PidB
PidC
error
PidA

24. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
A process can explicitly send an exit signal to another process using exit(Pid, Reason):
exit(PidB, error)
PidB
PidA
error
The calling process is not affected.
The processes do not need to be linked.

25. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
A process can trap exit signals using:
process_flag(trap_exit, true).
Incoming exit signals will be transformed into messages of the form: {'EXIT', Pid, Reason}
These exit messages are delivered to the process mailbox in the normal way.

26. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
PidC terminates with reason error, PidD is trapping exits:
PidB terminates, propagating the exit signal. PidD will receive an exit message
{'EXIT', PidC, error}.
error
error
PidA
PidA
PidB
PidB
PidC
PidD
PidE

27. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
Robust systems can be made by layering.

28. Erlang fault tolerance
Thomas Arts
Erlang fault tolerance
supervision trees and restart strategies P1 P2 P3 P1 P4 P3 P1 P2 P3 P4 P5 P6

29. Erlang component based development
Thomas Arts
Erlang component based development
recognize frequently occurring
patterns and transfer them into
standard components.
faster development
uniform code (maintenance)
less errors

30. Thomas Arts
Erlang
Developed with the application of the language constantly in mind
Practical usability more priority than purity

31. AXD 301, scalable ATM switch (up to 160 GB/sec)
Thomas Arts
Erlang is used
AXD 301, scalable ATM switch (up to 160 GB/sec)
four years work
more than 500,000 lines of Erlang
several hundreds of programmers

32. Erlang is used GPRS: next generation GSM network.
Thomas Arts
Erlang is used
GPRS: next generation GSM network.
Eigth times faster internet access in mobile phones
always connected
development in three countries, hundreds of people

33. Erlang is used The success of the language in industry is due to
Thomas Arts
Erlang is used
The success of the language in industry is due to
Language features
Support and libraries
Design patterns / architectures
easy to learn
close to way of thinking by building telecom products

34. Erlang is used www.erlang.org over 300 downloads per month
Thomas Arts
Erlang is used
over
300 downloads
per month
Become a user yourself!
passive: make a phonecall
active: download Erlang for free
easy to learn
close to way of thinking by building telecom products

35. The functional language for industry
Thomas Arts
Erlang
The functional language
for industry
easy to learn
close to way of thinking by building telecom products
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