Erlang - a complete development environment for concurrent programming RTLab. Kim Tae-Hyon

Contents  What is Erlang?  Erlang features  Sequential Programming  Concurrent Programming  Distribute Programming

What is Erlang?  Erlang is a general-purpose programming language and runtime environment  Erlang has built-in support for concurrency, distribution and fault tolerance  Erlang is used in several large telecommunication systems from EricssonEricsson

Erlang features  Concurrency  Distribution  Robustness  Soft real-time  Hot code upgrade  Incremental code loading  External Interface

Data Types  Term  A piece of data of any data type is called a term  Numbers  Integer (10, -234, 16#AB10F, $A)  Floats (17.368, , 12.34E-10)  Atoms  abcdef, start_with_a_lower_case, ‘Blanks can be quoted’  Tuples  {123, bcd}, {123, def, abc}, {abc, {def, 123}, jkl}, {}  Lists  [123, xyz], [123, def, abc], [{person, ‘Kim’, ‘Tae Hyon’}, {person, …}]  Variables  Abc, A_long_variable_name, AnObjectName

Data Types (Cont)  String  Not a data type in erlang  Bit string and Binaries  Red=2, Green=61, Blue=20.  Mem = >  >  > = Mem.  R1 = 2, G1 = 61, B1 = 20  Fun  Functional object  Fun1 = fun(x) -> X+1 end.  Fun1(2).  3

Data Types (Cont)  Pid  A Process Identifier  Record  -record(person, {name, age}).  new(Name, Age) ->  #person{name=Name, age=Age}.  1> person:new(ernie, 44).  {person,ernie,44}  Boolean  True, false

Sequential Programming  Pattern Matching  A = 10 (succeeds)  {B, C, D} = {10, foo, bar} (succeeds)  {A, A, B} = {abc, abc, foo} (succeeds)  {A, A, B} = {abc, def, foo} (fails)  [A, B, C] = [1, 2, 3] (succeeds)  [A, B, C, D] = [1, 2, 3] (fails)  [A, B|C] = [1,2,3,4,5,6,7] (succeeds)  [H|T] = [1,2,3,4] (succeeds)  [H|T] = [abc] (succeeds)  [H|T] = [] (fails)  {A, _, [B|_], {B}} = {abc, 23, [22, x], {22}} (succeeds)

Sequential Programming (Cont)

 Function Calls  module:func(Arg1, Arg2, …, Argn)  func(Arg1, Arg2, …, Argn)  Module System  -module(seminar_demo).  -export([double/1]).  double(X) ->times(X,2).  times(X, N) ->X * N.

Sequential Programming (Cont)

 Built In Functions(BIF)  date()  time()  length([1,2,3,4,5])  atom_to_list(an_atom)  list_to_tuple([1,2,3,4])  integer_to_list(2234)  tuple_to_list({})

Sequential Programming (Cont)  Function Syntax  func(Pattern1, Pattern2,...) ->... ;  func(Pattern1, Pattern2,...) ->... ; func(Pattern1, Pattern2,...) ->....  Function Example  area({square, Side}) ->  Side * Side;  area({circle, Radius}) ->  3 * Radius * Radius;  area({triangle, A, B, C}) ->  S = (A + B + C)/2,  math:sqrt(S*(S-A)*(S-B)*(S-C));  area(Other) ->  {invalid_object, Other}.

Sequential Programming (Cont)  Guarded Function Clauses  factorial(N) when N > 0 ->  N * factorial(N - 1);  factorial(0) -> 1.  Examples of Guards  is_atom(X)  is_binary(X)  Is_constant(X)  Is_function(X)  X == Y (equal)  X =:= Y (exactly equal -> 1==1.0 succeds, 1=:=1.0 fails) ...

Concurrent Programming  Creating a Process  Pid2 = spawn(Mod, Func, Args)  Simple Message Passing

Concurrent Programming (Cont)  An Echo Process

Concurrent Programming (Cont)  Selective Message Reception  Selection of Any Message

Concurrent Programming (Cont)  Pid Can Be Sent in Message  Registered Process  start() ->  Pid = spawn(num_anal, server, [])  register(analyser, Pid).  analyse(Seq) ->  analyser ! {self(),{analyse,Seq}},  receive  {analysis_result,R} ->  R  end.

Concurrent Programming (Cont)  Timeouts

Concurrent Programming (Cont)  Primitives For Exit Signal Handling  link(Pid) - Set a bi-directional link between the current process and the process Pid  process_flag(trap_exit, true) - Set the current process to convert exit signals to exit messages, these messages can then be received in a normal receive statement.  exit(Reason) - Terminates the process and generates an exit signal where the process termination information is Reason.

Concurrent Programming (Cont)  Exit Signal are Sent when Processes Crash  Exit Signals Propagate through Links

Concurrent Programming (Cont)  Processes can trap exit signals  receive  {'EXIT', P1, Why} -> ... exit signals...  {P3, Msg} -> ... normal messages...  end

Concurrent Programming (Cont)  Robust system made by layering

Distribute Programming  Nodes  A node is an executing erlang runtime system which has been given a name, using the command line flag -name or –sname  Node connections  spawn(Node, Module, Function, Arguments)  net_adm:ping(Node)

Distribute Programming (Cont) doris $ erl –name gandalf –setcookie abc 1>kvs:start(). true george $ erl –name bilbo –setcookie abc kvs, store, [weather, kvs true kvs, lookup, kvs {ok, cold}