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|
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<div id="sub_header"></div>
<div id="logo"><img src="ui/img/logo.svg"/></div>
</div>
<div id="footer">
<div id="footer_shadow"></div>
<h1>One day Erlang training</h1>
<h2>Thinking in Erlang, Nine Nines</h2>
</div>
</div>
<div class="presentation">
<div class="slide">
<h1>Thinking in Erlang</h1>
<h2>One day Erlang training</h2>
<h3>Loïc Hoguin - @lhoguin</h3>
<h4>Erlang Cowboy and Nine Nines Founder</h4>
</div>
<div class="slide">
<h1>Erlang installation</h1>
</div>
<div class="slide">
<h1>Where to find Erlang</h1>
<ul>
<li>Website: http://erlang.org</li>
<li>Source: https://github.com/erlang/otp</li>
<li>Arch Linux package: pacman</li>
<li>Other packages: http://www.erlang.org/download.html</li>
</ul>
</div>
<div class="slide">
<h1>Installing</h1>
<ul>
<li>Arch Linux: pacman -S erlang</li>
<li>Other platforms: see installer</li>
<li>Ad-hoc install: https://github.com/spawngrid/kerl</li>
</ul>
</div>
<div class="slide">
<h1>Where to find help</h1>
<ul>
<li>Official documentation: http://www.erlang.org/erldoc</li>
<li>Command line: erl -man <module></li>
<li>Books: Programming Erlang, LYSE</li>
<li>Mailing lists: http://erlang.org/community.html</li>
<li>IRC: #erlang on Freenode</li>
</ul>
</div>
<div class="slide">
<h1>Erlang the Movie</h1>
<ul>
<li>http://www.youtube.com/watch?v=xrIjfIjssLE</li>
</ul>
</div>
<div class="slide">
<h1>The shell</h1>
<ul>
<li>erl</li>
<li>Ctrl+G</li>
<li>Ctrl+C</li>
</ul>
</div>
<div class="slide">
<h1>Hello world</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> "Hello world!".
]]></script></div>
</div>
<div class="slide">
<h1>What's Erlang?</h1>
</div>
<div class="slide">
<h1>The question</h1>
<ul>
<li>"How do we make reliable systems from components which fail?</li>
</ul>
</div>
<div class="slide">
<h1>Black boxes</h1>
<ul>
<li>We build systems of many isolated black boxes that communicate by talking to each other</li>
</ul>
</div>
<div class="slide">
<h1>Erlang black boxes</h1>
<ul>
<li>Nodes</li>
<li>Processes</li>
<li>Ports</li>
<li>ets tables</li>
</ul>
</div>
<div class="slide">
<h1>Concurrent programming language</h1>
<ul>
<li>Large number of processes</li>
<li>Complete isolation of processes</li>
<li>No sharing of data</li>
<li>Location transparency</li>
<li>Pure message passing</li>
</ul>
</div>
<div class="slide">
<h1>Concurrency?</h1>
<ul>
<li>You already understand concurrency</li>
<li>The world is parallel</li>
<li>The world is made of many black boxes</li>
<li>You need concurrency to model the real-world</li>
<li>Concurrency makes it easy to build scalable, distributed applications</li>
</ul>
</div>
<div class="slide">
<h1>Modeling the real world</h1>
<ul>
<li>"Making a real-world application is based on observation of the concurrency patterns and message channels of the application"</li>
</ul>
</div>
<div class="slide">
<h1>Black boxes fail</h1>
<ul>
<li>Hardware failure (just replace the component)</li>
<li>Software failure (depends on the error reason)</li>
<li>Concurrency and isolation ensures only one black box fails instead of the whole system</li>
<li>Erlang processes can detect and identify failure to repair the system</li>
</ul>
</div>
<div class="slide">
<h1>Fault detection</h1>
<ul>
<li>Processes can be explicitly linked</li>
<li>All linked processes are alerted when a process dies</li>
</ul>
</div>
<div class="slide">
<h1>Fault identification</h1>
<ul>
<li>Processes say why they die</li>
</ul>
</div>
<div class="slide">
<h1>Let it crash</h1>
<ul>
<li>Use links to detect and identify errors</li>
<li>Linked process then decides whether to restart the dead process</li>
<li>Restarting = starting a new process with the same initial arguments</li>
</ul>
</div>
<div class="slide">
<h1>Software evolves</h1>
<ul>
<li>Reliable systems must be able to be upgraded without being stopped</li>
</ul>
</div>
<div class="slide">
<h1>Erlang in 6 key points</h1>
<ul>
<li>Concurrency (processes)</li>
<li>Error encapsulation (isolation)</li>
<li>Fault detection (what failed)</li>
<li>Fault identification (why it failed)</li>
<li>Live code upgrade (evolving systems)</li>
<li>Stable storage (crash recovery)</li>
</ul>
</div>
<div class="slide">
<h1>What's OTP?</h1>
</div>
<div class="slide">
<h1>OTP</h1>
<ul>
<li>A framework for building fault tolerant distributed applications</li>
</ul>
</div>
<div class="slide">
<h1>OTP provides middlewares</h1>
<ul>
<li>Releases (packaging, upgrades)</li>
<li>Applications</li>
<li>Supervisors</li>
<li>Client/server processes</li>
<li>Finite state machines</li>
<li>Event handlers</li>
</ul>
</div>
<div class="slide">
<h1>OTP provides tools</h1>
<ul>
<li>Development</li>
<li>Testing</li>
<li>Debugging</li>
<li>Monitoring</li>
</ul>
</div>
<div class="slide">
<h1>Overview of an Erlang system</h1>
</div>
<div class="slide">
<h1>Release</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> application:start(sasl).
ok
...
=PROGRESS REPORT==== 9-Oct-2013::06:51:45 ===
application: sasl
started_at: nonode@nohost
2> release_handler:which_releases().
[{"OTP APN 181 01","R16B02",
["kernel-2.16.3","stdlib-1.19.3","sasl-2.3.3"],
permanent}]
]]></script></div>
</div>
<div class="slide">
<h1>Nodes</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> node().
nonode@nohost
2> nodes().
[]
]]></script></div>
</div>
<div class="slide">
<h1>Nodes (distributed mode)</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
(a@localhost)1> net_adm:ping(b@localhost).
pong
(a@localhost)2> nodes().
[b@localhost]
(b@localhost)1> nodes().
[a@localhost]
]]></script></div>
</div>
<div class="slide">
<h1>Processes</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> i().
Pid Initial Call Heap Reds Msgs
Registered Current Function Stack
<0.0.0> otp_ring0:start/2 1598 3339 0
init init:loop/1 2
<0.3.0> erlang:apply/2 2586 136197 0
erl_prim_loader erl_prim_loader:loop/3 6
<0.6.0> gen_event:init_it/6 376 220 0
error_logger gen_event:fetch_msg/5 9
<0.7.0> erlang:apply/2 1598 434 0
application_controlle gen_server:loop/6 7
...
Total 39469 310325 0
220
ok
]]></script></div>
</div>
<div class="slide">
<h1>Registered processes</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> erlang:registered().
[application_controller,user_drv,kernel_safe_sup,rex,
standard_error,kernel_sup,global_group,standard_error_sup,
global_name_server,inet_db,file_server_2,user,init,
code_server,erl_prim_loader,error_logger]
2> global:registered_names().
[]
]]></script></div>
</div>
<div class="slide">
<h1>Ets tables</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> ets:i().
id name type size mem owner
----------------------------------------------------------------------------
13 code set 262 9659 code_server
4110 code_names set 54 6687 code_server
8207 shell_records ordered_set 0 89 <0.27.0>
ac_tab ac_tab set 6 841 application_controller
file_io_servers file_io_servers set 0 299 file_server_2
global_locks global_locks set 0 299 global_name_server
global_names global_names set 0 299 global_name_server
global_names_ext global_names_ext set 0 299 global_name_server
global_pid_ids global_pid_ids bag 0 299 global_name_server
global_pid_names global_pid_names bag 0 299 global_name_server
inet_cache inet_cache bag 0 299 inet_db
inet_db inet_db set 29 622 inet_db
inet_hosts_byaddr inet_hosts_byaddr bag 0 299 inet_db
inet_hosts_byname inet_hosts_byname bag 0 299 inet_db
inet_hosts_file_byaddr inet_hosts_file_byaddr bag 0 299 inet_db
inet_hosts_file_byname inet_hosts_file_byname bag 0 299 inet_db
ok
]]></script></div>
</div>
<div class="slide">
<h1>Applications</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> application:info().
[{loaded,[{kernel,"ERTS CXC 138 10","2.16.3"},
{stdlib,"ERTS CXC 138 10","1.19.3"}]},
{loading,[]},
{started,[{stdlib,permanent},{kernel,permanent}]},
{start_p_false,[]},
{running,[{stdlib,undefined},{kernel,<0.9.0>}]},
{starting,[]}]
]]></script></div>
</div>
<div class="slide">
<h1>Modules</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> erlang:loaded().
[erl_internal,otp_internal,erl_parse,erl_scan,io,sets,dict,
ordsets,erl_lint,file_io_server,orddict,erl_eval,c,
error_logger_tty_h,kernel_config,shell,io_lib_format,
proplists,io_lib,edlin,group,user_drv,user_sup,
supervisor_bridge,standard_error,ram_file,file,beam_lib,
code_server|...]
]]></script></div>
</div>
<div class="slide">
<h1>GUI</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> observer:start().
ok
]]></script></div>
</div>
<div class="slide">
<h1>The building blocks</h1>
</div>
<div class="slide">
<h1>Code and data</h1>
<ul>
<li>Two types of building blocks</li>
<li>The code that the programs in the system execute</li>
<li>The programs themselves and their associated state</li>
</ul>
</div>
<div class="slide">
<h1>Sounds familiar?</h1>
<ul>
<li>Erlang is an operating system for your code</li>
</ul>
</div>
<div class="slide">
<h1>Code</h1>
<img src="pics/building_blocks_code.png"/>
</div>
<div class="slide">
<h1>Releases</h1>
<ul>
<li>A self-contained package for running your node</li>
<li>Contains the full Erlang VM and all files needed</li>
<li>Can be deployed and ran directly on target machines</li>
<li>Capable of being fully upgraded live (release upgrades)</li>
</ul>
</div>
<div class="slide">
<h1>Applications 1</h1>
<ul>
<li>A library application is a set of related modules and files</li>
<li>An application is the above plus a set of running processes (when started)</li>
<li>Allows grouping dependent modules together</li>
</ul>
</div>
<div class="slide">
<h1>Modules</h1>
<ul>
<li>A box where we put related functions</li>
<li>Modules can be upgraded live</li>
</ul>
</div>
<div class="slide">
<h1>Functions</h1>
<ul>
<li>A small program</li>
<li>Functions may take parameters and always return a value</li>
<li>Only exported functions can be called from outside a module</li>
</ul>
</div>
<div class="slide">
<h1>Data</h1>
<img src="pics/building_blocks_data.png"/>
</div>
<div class="slide">
<h1>Nodes</h1>
<ul>
<li>A running instance of the Erlang VM</li>
<li>Using more than one enables scaling, distribution and fault tolerance</li>
</ul>
</div>
<div class="slide">
<h1>Application 2</h1>
<ul>
<li>An instance of a running application</li>
<li>Allows grouping dependent processes together</li>
<li>Applications should have a single overall purpose</li>
</ul>
</div>
<div class="slide">
<h1>Processes</h1>
<ul>
<li>An instance of a program being executed</li>
<li>Processes should have a single purpose</li>
</ul>
</div>
<div class="slide">
<h1>Process registry</h1>
<ul>
<li>A mechanism to name processes</li>
<li>Use it to quickly find important processes and simplify your code</li>
</ul>
</div>
<div class="slide">
<h1>Ets tables</h1>
<ul>
<li>A process-like in-memory key-value store</li>
<li>Always linked to a certain process</li>
<li>Table can be inherited by another process on failure</li>
<li>Much faster concurrent access than normal processes</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 1</h1>
<ul>
<li>Write a simplified diagram of a fault tolerant system using the above building blocks</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 2</h1>
<ul>
<li>Add a Web layer to the previous example so that browsers can access your system</li>
</ul>
</div>
<div class="slide">
<h1>Types</h1>
</div>
<div class="slide">
<h1>Integer</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> 42.
42
2> 1 + 1.
2
3> 3 * 3.
9
4> 9 div 3.
]]></script></div>
</div>
<div class="slide">
<h1>Atom 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> blue.
blue
2> erlang.
erlang
3> 'quoted form'.
'quoted form'
4> erlang =:= 'erlang'.
true
]]></script></div>
</div>
<div class="slide">
<h1>Atom 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
5> M = io.
io
6> F = format.
format
7> M:F("Hello world!").
Hello world!
ok
]]></script></div>
</div>
<div class="slide">
<h1>List 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> [].
[]
2> [1, 2, 3].
[1,2,3]
3> [42, [blue, red], cats].
[42,[blue,red],cats]
4> [1|[2|[3]]].
[1,2,3]
]]></script></div>
</div>
<div class="slide">
<h1>List 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
5> Str = "Hello world!".
"Hello world!"
6> [$H, $e|Str].
"HeHello world!"
7> [0|Str].
[0,72,101,108,108,111,32,119,111,114,108,100,33]
]]></script></div>
</div>
<div class="slide">
<h1>List 3</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Str = "123".
"123"
2> list_to_integer(Str).
123
3> list_to_atom(Str).
'123'
4> integer_to_list(123).
"123"
]]></script></div>
</div>
<div class="slide">
<h1>List 4</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> list_to_existing_atom("ok").
ok
2> list_to_existing_atom("hehehe").
** exception error: bad argument
in function list_to_existing_atom/1
called as list_to_existing_atom("hehehe")
]]></script></div>
</div>
<div class="slide">
<h1>Tuple</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> {}.
{}
2> {ok, 42}.
{ok,42}
3> {error, "Can't connect", [{file, "..."}, {line, 42}]}.
{error,"Can't connect",[{file,"..."},{line,42}]}
4> element(2, {ok, 42}).
42
]]></script></div>
</div>
<div class="slide">
<h1>Map</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> #{}.
#{}
2> Food = #{color => blue, taste => bitter}.
#{color => blue,taste => bitter}
3> Food#{color => red}.
#{color => red,taste => bitter}
4> #{taste => bitter} = Food.
* 1: illegal pattern
5> #{taste := bitter} = Food.
#{color => blue,taste => bitter}
]]></script></div>
</div>
<div class="slide">
<h1>Pid</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> self().
<0.33.0>
2> spawn(fun() -> ok end).
<0.36.0>
3> spawn(fun() -> ok end).
<0.38.0>
4> spawn(fun() -> ok end).
<0.40.0>
]]></script></div>
</div>
<div class="slide">
<h1>Reference</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> make_ref().
#Ref<0.0.0.32>
2> R1 = make_ref().
#Ref<0.0.0.37>
3> R2 = make_ref().
#Ref<0.0.0.42>
4> R1 =:= R2.
false
]]></script></div>
</div>
<div class="slide">
<h1>Fun</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> F = fun() -> ok end.
#Fun<erl_eval.20.80484245>
2> F().
ok
3> G = fun(true) -> happy; (false) -> sad end.
#Fun<erl_eval.6.80484245>
4> G(true).
happy
5> G(false).
sad
]]></script></div>
</div>
<div class="slide">
<h1>Type identification</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> is_integer("123").
false
2> is_integer(123).
true
3> is_integer(ok).
false
4> is_atom(ok).
true
5> is_tuple(ok).
false
6> is_tuple({ok, 123}).
true
]]></script></div>
</div>
<div class="slide">
<h1>Other types</h1>
<ul>
<li>Float</li>
<li>Binary</li>
<li>Maps (R17+)</li>
<li>Improper lists</li>
<li>Port</li>
</ul>
</div>
<div class="slide">
<h1>Modules and functions</h1>
</div>
<div class="slide">
<h1>Structure of a module</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
-module(my_module).
-export([f/0, g/2, ...]).
f() ->
%% @todo Implement this function!!
ok.
g(A, B) when is_integer(A), is_integer(B) ->
A * B.
]]></script></div>
</div>
<div class="slide">
<h1>Exports</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
-export([f/0, g/2, ...]).
-export([h/1]).
]]></script></div>
</div>
<div class="slide">
<h1>Function definition</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f() ->
ok.
g(A, B) ->
A * B.
]]></script></div>
</div>
<div class="slide">
<h1>Guards</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
g(A, B) when is_integer(A), is_integer(B) ->
A * B.
h(C) when C > 0 ->
ok.
]]></script></div>
</div>
<div class="slide">
<h1>Where can guards be used?</h1>
<ul>
<li>Function clauses</li>
<li>Case clauses</li>
<li>Receive clauses</li>
<li>if</li>
</ul>
</div>
<div class="slide">
<h1>Pattern matching in function clauses</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
is_blue(blue) ->
true.
]]></script></div>
</div>
<div class="slide">
<h1>Function clauses</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
is_blue(blue) ->
true;
is_blue(_) ->
false.
]]></script></div>
</div>
<div class="slide">
<h1>case .. of</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
is_blue(Color) ->
case Color of
blue ->
true;
_ ->
false
end.
]]></script></div>
</div>
<div class="slide">
<h1>Local function call</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
paint(Color) ->
case is_blue(Color) of
true -> paint_window();
false -> paint_wall()
end.
is_blue(blue) ->
true;
is_blue(_) ->
false.
%% ...
]]></script></div>
</div>
<div class="slide">
<h1>Remote function call</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
get_data(Filename) ->
{ok, Data} = file:read_file(Filename),
Data.
]]></script></div>
</div>
<div class="slide">
<h1>Pattern matching with =</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f(Color) ->
blue = Color,
ok.
get_data(Filename) ->
{ok, Data} = file:read_file(Filename),
Data.
]]></script></div>
</div>
<div class="slide">
<h1>Expressions</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
get_data(Filename) ->
{ok, Data} = file:read_file(Filename),
io:format("~s~n", [Data]),
Data.
]]></script></div>
</div>
<div class="slide">
<h1>Function return value</h1>
<ul>
<li>When they return, all functions return a value</li>
<li>It is always the result of the last expression</li>
<li>Some functions never return</li>
</ul>
</div>
<div class="slide">
<h1>Recursion</h1>
</div>
<div class="slide">
<h1>Recursion explained</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f() ->
f().
]]></script></div>
<ul>
<li>"This will make the VM run out of memory!"</li>
<li>Will it? Try it.</li>
</ul>
</div>
<div class="slide">
<h1>Recursing through a list</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f([]) ->
ok;
f([H|T]) ->
io:format("~p", [H]),
f(T).
]]></script></div>
</div>
<div class="slide">
<h1>Transforming a list 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f([]) ->
[];
f([H|T]) ->
[H * 2|f(T)].
]]></script></div>
</div>
<div class="slide">
<h1>Accumulator</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f(List) ->
f(List, []).
f([], Acc) ->
Acc;
f([H|T], Acc) ->
f(T, [H|Acc]).
]]></script></div>
</div>
<div class="slide">
<h1>Transforming a list 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f(List) ->
f(List, []).
f([], Acc) ->
lists:reverse(Acc);
f([H|T], Acc) ->
f(T, [H * 2|Acc]).
]]></script></div>
</div>
<div class="slide">
<h1>Exercise 3</h1>
<ul>
<li>Write a function that applies a fun over all elements of a list and returns it</li>
</ul>
</div>
<div class="slide">
<h1>Transforming a list 3</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f(List) ->
map(fun (N) -> N * 2 end, List).
map(Fun, List) ->
map(Fun, List, []).
map(_, [], Acc) ->
lists:reverse(Acc);
map(Fun, [H|T], Acc) ->
map(Fun, T, [Fun(H)|Acc]).
]]></script></div>
</div>
<div class="slide">
<h1>Transforming a list 4</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
f(List) ->
[N * 2 || N <- List].
]]></script></div>
</div>
<div class="slide">
<h1>Exercise 4</h1>
<ul>
<li>Implement a function that sorts a list of Erlang terms</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 5</h1>
<ul>
<li>Implement a function that removes all non-prime numbers from a list</li>
</ul>
</div>
<div class="slide">
<h1>Concurrency and message passing</h1>
</div>
<div class="slide">
<h1>Exercise 6</h1>
<ul>
<li>What's a process?</li>
</ul>
</div>
<div class="slide">
<h1>Spawn</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> spawn(fun() -> ok end).
<0.35.0>
2> spawn(fun() -> timer:sleep(10000) end).
<0.37.0>
]]></script></div>
</div>
<div class="slide">
<h1>Order of execution is undefined</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
8> [spawn(fun () -> erlang:display(N) end) || N <- lists:seq(1, 100)].
1
2
3
4
6
5
7
...
]]></script></div>
</div>
<div class="slide">
<h1>Processes are cheap</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> L = lists:seq(1, 10000).
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26,27,28,29|...]
2> [spawn(fun () -> receive ok -> ok end end) || _ <- L].
[<0.36.0>,<0.37.0>,<0.38.0>,<0.39.0>,<0.40.0>,<0.41.0>,
<0.42.0>,<0.43.0>,<0.44.0>,<0.45.0>,<0.46.0>,<0.47.0>,
<0.48.0>,<0.49.0>,<0.50.0>,<0.51.0>,<0.52.0>,<0.53.0>,
<0.54.0>,<0.55.0>,<0.56.0>,<0.57.0>,<0.58.0>,<0.59.0>,
<0.60.0>,<0.61.0>,<0.62.0>,<0.63.0>,<0.64.0>|...]
]]></script></div>
</div>
<div class="slide">
<h1>Processes are isolated</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> spawn(fun () -> 1 div 0 end).
<0.35.0>
=ERROR REPORT==== 11-Oct-2013::13:19:07 ===
Error in process <0.35.0> with exit value: {badarith,[{erlang,div,[1,0],[]}]}
2>
]]></script></div>
</div>
<div class="slide">
<h1>Message passing</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> self() ! hello.
hello
2> flush().
Shell got hello
ok
]]></script></div>
</div>
<div class="slide">
<h1>receive 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> self() ! hello.
hello
2> receive V -> V end.
hello
]]></script></div>
</div>
<div class="slide">
<h1>receive 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Pid = spawn(fun () -> receive V -> io:format("yay! ~p~n", [V]) end end).
<0.35.0>
2> Pid ! hello.
yay! hello
hello
]]></script></div>
</div>
<div class="slide">
<h1>receive 3</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> self() ! hello.
hello
2> receive hello -> how_are_you; Any -> please_dont_be_impolite end.
how_are_you
3> self() ! yo.
yo
4> receive hello -> how_are_you; Any -> please_dont_be_impolite end.
please_dont_be_impolite
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> receive V -> V after 1000 -> nothing end.
nothing
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
2> self() ! something.
something
3> receive V -> V after 1000 -> nothing end.
something
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 3</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
4> receive after 1000 -> timeout end.
timeout
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 4</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
5> receive V -> V after infinity -> nothing end.
User switch command
--> i
--> c
** exception exit: killed
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 5</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
6> spawn(fun () -> receive V -> io:format("yay! ~p~n", [V]) after 1000 -> io:format("nothing :(~n") end end).
<0.41.0>
nothing :(
]]></script></div>
</div>
<div class="slide">
<h1>receive .. after 6</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
7> Pid = spawn(fun () -> receive M -> io:format("yay! ~p~n", [M]) after 10000 -> io:format("nothing :(~n") end end).
<0.35.0>
8> Pid ! yay.
yay! yay
yay
]]></script></div>
</div>
<div class="slide">
<h1>Selective receive</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> self() ! blue.
blue
2> receive red -> ok after 1000 -> timeout end.
timeout
3> flush().
Shell got blue
ok
]]></script></div>
</div>
<div class="slide">
<h1>Receive loop 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
-module(recv_loop).
-export([start/0, loop/0]).
start() ->
spawn(fun loop/0).
loop() ->
receive
Msg ->
io:format("yay! ~p~n", [Msg])
end,
loop().
]]></script></div>
</div>
<div class="slide">
<h1>Receive loop 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> c(recv_loop).
{ok,recv_loop}
2> Pid = recv_loop:start().
<0.41.0>
3> Pid ! hello.
yay! hello
hello
4> Pid ! world.
yay! world
world
]]></script></div>
</div>
<div class="slide">
<h1>Exercise 7</h1>
<ul>
<li>Add a function to stop recv_loop processes</li>
</ul>
</div>
<div class="slide">
<h1>Process state</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
loop() ->
loop(0).
loop(Counter) ->
receive
Msg ->
io:format("yay ~p! ~p~n", [Counter, Msg])
end,
loop(Counter + 1).
]]></script></div>
</div>
<div class="slide">
<h1>Exercise 8</h1>
<ul>
<li>Make a function for incrementing a value in the recv_loop process</li>
<li>Make a function for retrieving this value</li>
</ul>
</div>
<div class="slide">
<h1>In the previous episode</h1>
<ul>
<li>A function that sends a message and doesn't expect a message in response is called a cast</li>
<li>A function that sends a message and expect a message in response is called a call</li>
<li>A process keeps state by passing it in function arguments</li>
</ul>
</div>
<div class="slide">
<h1>Cast</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
cast(Pid, Msg) ->
Pid ! {cast, Msg},
ok.
]]></script></div>
</div>
<div class="slide">
<h1>Call</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
call(Pid, Msg) ->
call(Pid, Msg, 5000).
call(Pid, Msg, Timeout) ->
Pid ! {call, Msg},
receive
{call_response, Response} ->
Response
after Timeout ->
exit(timeout)
end.
]]></script></div>
</div>
<div class="slide">
<h1>Process registry</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> register(myself, self()).
true
2> myself ! hello.
hello
3> flush().
Shell got hello
ok
4> whereis(myself).
<0.33.0>
5> self().
<0.33.0>
6> spawn(fun () -> register(myself, self()) end).
<0.40.0>
=ERROR REPORT==== 11-Oct-2013::14:40:47 ===
Error in process <0.40.0> with exit value: {badarg,[{erlang,register,[myself,<0.40.0>],[]}]}
]]></script></div>
</div>
<div class="slide">
<h1>Remote error handling</h1>
</div>
<div class="slide">
<h1>Unexpected consequences</h1>
<ul>
<li>What happens if the process you call crashes?</li>
</ul>
</div>
<div class="slide">
<h1>Monitors 1</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Pid = spawn(fun () -> receive stop -> ok end end).
<0.36.0>
2> monitor(process, Pid).
#Ref<0.0.0.38>
3> Pid ! stop.
stop
4> flush().
Shell got {'DOWN',#Ref<0.0.0.38>,process,<0.36.0>,normal}
ok
]]></script></div>
</div>
<div class="slide">
<h1>Monitors 2</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Pid = spawn(fun () -> receive stop -> 1 = 2 end end).
<0.35.0>
2> Ref = monitor(process, Pid).
#Ref<0.0.0.36>
3> Pid ! stop.
stop
=ERROR REPORT==== 11-Oct-2013::16:10:59 ===
Error in process <0.35.0> with exit value: {{badmatch,2},[{erl_eval,expr,3,[]}]}
4> receive {'DOWN', Ref, process, Pid, Reason} -> Reason end.
{{badmatch,2},[{erl_eval,expr,3,[]}]}
]]></script></div>
</div>
<div class="slide">
<h1>Exercise 9</h1>
<ul>
<li>Modify the call function to detect process failure</li>
</ul>
</div>
<div class="slide">
<h1>Is that really necessary?</h1>
<ul>
<li>"My programs never have bugs!"</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 10</h1>
<ul>
<li>Identify more potential issues that may happen when performing a call</li>
</ul>
</div>
<div class="slide">
<h1>Safe RPC</h1>
<ul>
<li>Let's learn from Erlang/OTP itself</li>
<li>Take a look at gen.erl</li>
</ul>
</div>
<div class="slide">
<h1>Links 1</h1>
<img src="pics/links_crash_1.png"/>
</div>
<div class="slide">
<h1>Links 2</h1>
<img src="pics/links_crash_2.png"/>
</div>
<div class="slide">
<h1>Links 3</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Pid = self().
<0.33.0>
2> Child = spawn(fun () -> link(Pid), receive _ -> exit(booya) end end).
<0.36.0>
3> Child ! bye.
** exception exit: booya
]]></script></div>
</div>
<div class="slide">
<h1>Links 4</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> Child = spawn_link(fun () -> receive _ -> exit(booya) end end).
<0.35.0>
2> Child ! bye.
** exception exit: booya
]]></script></div>
</div>
<div class="slide">
<h1>Links 5</h1>
<img src="pics/links_trap_exit_1.png"/>
</div>
<div class="slide">
<h1>Links 6</h1>
<img src="pics/links_trap_exit_2.png"/>
</div>
<div class="slide">
<h1>Links 7</h1>
<div><script type="syntaxhighlighter" class="brush: erlang"><![CDATA[
1> erlang:process_flag(trap_exit, true).
false
2> Child = spawn_link(fun () -> receive _ -> exit(booya) end end).
<0.36.0>
3> Child ! bye.
bye
4> flush().
Shell got {'EXIT',<0.36.0>,booya}
ok
]]></script></div>
</div>
<div class="slide">
<h1>Monitors vs links</h1>
<ul>
<li>Monitors are unidirectional</li>
<li>Links are bidirectional</li>
<li>Monitors just send a message</li>
<li>Links send an exit signal</li>
</ul>
</div>
<div class="slide">
<h1>Manage the unexpected</h1>
<ul>
<li>What should you do when a process crash?</li>
<li>Why do processes crash, anyway?</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 11</h1>
<ul>
<li>Create a process that will always restart crashing processes</li>
</ul>
</div>
<div class="slide">
<h1>Exercise 12</h1>
<ul>
<li>Is this method truly fault tolerant?</li>
</ul>
</div>
<div class="slide">
<h1>Supervision tree</h1>
<ul>
<li>Let's take a quick look at OTP applications and supervision trees again</li>
</ul>
</div>
<div class="slide">
<h1>Food for thoughts</h1>
<ul>
<li>OTP comes with everything we just saw</li>
<li>The gen_server behavior implements client/server as a process (calls and casts)</li>
<li>The supervisor behavior implements supervision with tons of options and safety included</li>
<li>The application behavior implements the starting and stopping of OTP applications</li>
<li>They are battle tested and make upgrading your code easy</li>
</ul>
</div>
<div class="slide">
<h1>Final exercise</h1>
</div>
<div class="slide">
<h1>Erlang chat</h1>
<ul>
<li>Write a program that allows different Erlang shells to communicate in a common chat room</li>
<li>Bonus: Make that program fault tolerant</li>
<li>Bonus: Make that program OTP compliant</li>
</ul>
</div>
<div class="slide">
<h1>Questions</h1>
<ul>
<li><a href="http://ninenines.eu">http://ninenines.eu</a></li>
<li>Twitter: @lhoguin</li>
<li>IRC: #erlang and #ninenines on Freenode</li>
</ul>
</div>
</div>
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