merge(erlang-presentation): Merge at //presentations/erlang-2016

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Vincent Ambo 2019-12-21 00:38:42 +00:00
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slidenumbers: true
Erlang.
======
### Fault-tolerant, concurrent programming.
---
## A brief history of Erlang
---
![](https://www.ericsson.com/thinkingahead/the-networked-society-blog/wp-content/uploads/2014/09/bfW5FSr.jpg)
^ Telefontornet in Stockholm, around 1890. Used until 1913.
---
![](https://3.bp.blogspot.com/-UF7W9yTUO2g/VBqw-1HNTzI/AAAAAAAAPeg/KvsMbNSAcII/s1600/6835942484_1531372d8f_b.jpg)
^ Telephones were operated manually at Switchboards. Anyone old enough to remember? I'm certainly not.
---
![fit](https://russcam.github.io/fsharp-akka-talk/images/ericsson-301-AXD.png)
^ Eventually we did that in software, and we got better at it over time. Ericsson AXD 301, first commercial Erlang switch. But lets take a step back.
---
## Phone switches must be ...
Highly concurrent
Fault-tolerant
Distributed
(Fast!)
![right 150%](http://learnyousomeerlang.com/static/img/erlang-the-movie.png)
---
## ... and so is Erlang!
---
## Erlang as a whole:
- Unique process model (actors!)
- Built-in fault-tolerance & error handling
- Distributed processes
- Three parts!
---
## Part 1: Erlang, the language
- Functional
- Prolog-inspired syntax
- Everything is immutable
- *Extreme* pattern-matching
---
### Hello Joe
```erlang
hello_joe.
```
---
### Hello Joe
```erlang
-module(hello1).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.
```
---
### Hello Joe
```erlang
-module(hello1).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.
% 1> c(hello1).
% {ok,hello1}
% 2> hello1:hello_joe().
% hello_joe
```
---
### Hello Joe
```erlang
-module(hello2).
-export([hello/1]).
hello(Name) ->
io:format("Hello ~s!~n", [Name]).
% 3> c(hello2).
% {ok,hello2}
% 4> hello2:hello("Joe").
% Hello Joe!
% ok
```
---
## [fit] Hello ~~world~~ Joe is boring!
## [fit] Lets do it with processes.
---
### Hello Server
```erlang
-module(hello_server).
-export([start_server/0]).
start_server() ->
spawn(fun() -> server() end).
server() ->
receive
{greet, Name} ->
io:format("Hello ~s!~n", [Name]),
server()
end.
```
---
## [fit] Some issues with that ...
- What about unused messages?
- What if the server crashes?
---
## [fit] Part 2: Open Telecom Platform
### **It's called Erlang/OTP for a reason.**
---
# OTP: An Application Framework
- Supervision - keep processes alive!
- OTP Behaviours - common process patterns
- Extensive standard library
- Error handling, debuggers, testing, ...
- Lots more!
^ Standard library includes lots of things from simple network libraries over testing frameworks to cryptography, complete LDAP clients etc.
---
# Supervision
![inline](http://erlang.org/doc/design_principles/sup6.gif)
^ Supervision keeps processes alive, different restart behaviours, everything should be supervised to avoid "process" (and therefore memory) leaks
---
# OTP Behaviours
* `gen_server`
* `gen_statem`
* `gen_event`
* `supervisor`
^ gen = generic. explain server, explain statem, event = event handling with registered handlers, supervisor ...
---
`gen_server`
---
## [fit] Part 3: BEAM
### Bogdan/Bjørn Erlang Abstract machine
---
## A VM for Erlang
* Many were written, BEAM survived
* Concurrent garbage-collection
* Lower-level bytecode than JVM
* Very open to new languages
(Elixir, LFE, Joxa, ...)
---
## What next?
* Ole's talk, obviously!
* Learn You Some Erlang!
www.learnyousomeerlang.com
* Watch *Erlang the Movie*
* (soon!) Join the Oslo BEAM meetup group
---
# [fit] Questions?
`@tazjin`

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-module(hello).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.

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-module(hello1).
-export([hello_joe/0]).
hello_joe() ->
hello_joe.

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-module(hello2).
-export([hello/1]).
hello(Name) ->
io:format("Hey ~s!~n", [Name]).
% 3> c(hello2).
% {ok,hello2}
% 4> hello2:hello("Joe").
% Hello Joe!
% ok

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-module(hello_server).
-export([start_server/0, server/0]).
start_server() ->
spawn(fun() -> server() end).
server() ->
receive
{greet, Name} ->
io:format("Hello ~s!~n", [Name]),
hello_server:server()
end.

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-module(hello_server2).
-behaviour(gen_server).
-compile(export_all).
%%% Start callback for supervisor
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
%%% gen_server callbacks
init([]) ->
{ok, sets:new()}.
handle_call({greet, Name}, _From, State) ->
io:format("Hello ~s!~n", [Name]),
NewState = sets:add_element(Name, State),
{reply, ok, NewState};
handle_call({bye, Name}, _From, State) ->
io:format("Goodbye ~s!~n", [Name]),
NewState = sets:del_element(Name, State),
{reply, ok, NewState}.
terminate(normal, State) ->
[io:format("Goodbye ~s!~n", [Name]) || Name <- State],
ok.
%%% Unused gen_server callbacks
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_info(_Info, State) ->
{noreply, State}.
handle_cast(_Request, State) ->
{noreply, State}.

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-module(hello_sup).
-behaviour(supervisor).
-export([start_link/0, init/1]).
%%% Module API
start_link() ->
supervisor:start_link({local, ?MODULE}, ?MODULE, []).
%%% Supervisor callbacks
init([]) ->
Children = [hello_spec()],
{ok, { {one_for_one, 5, 10}, Children}}.
%%% Private
hello_spec() ->
#{id => hello_server2,
start => {hello_server2, start_link, []},
restart => permanent,
shutdown => 5000,
type => worker,
module => [hello_server2]}.