What's ahead for Elixir: v1.2 and GenRouter

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@elixirlang / elixir-lang.org

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Elixir v1.0 • September/2014 • >180 contributors • 3 books out! • First Elixirconf!

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Extensibility • Web infrastructure • Embedded systems • Financial/Video platforms • Graphical User Interfaces

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Elixir v1.1

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Elixir v1.1 • September/2015 • >295 contributors • ~ 1000 packages on hex.pm • > 6.5million downloads

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Application.fetch_env!/2 Keyword.get_and_update/3 Keyword.get_lazy/3 Keyword.pop_lazy/3 Keyword.put_new_lazy/3 Map.get_and_update/3 Map.get_lazy/3 Map.pop_lazy/3 Map.put_new_lazy/3 Enum.dedup/1 Enum.dedup_by/2 Enum.min_max/1 Enum.min_max_by/2 Enum.random/1 Enum.reduce_while/3 Enum.reverse_slice/3 Enum.take_random/2 More functions File.lstat/1 File.lstat!/1 File.rename/2 Integer.digits/2 Integer.undigits/2 GenServer.whereis/1 Process.hibernate/3 Stream.dedup/1 Stream.dedup_by/2 Stream.transform/4 String.jaro_distance/2 String.splitter/3 StringIO.flush/1 Task.yield/2 Task.shutdown/2 Tuple.append/2 URI.to_string/1

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Enum iex> Enum.dedup([1, 1, 2, 2, 1, 1]) [1, 2, 1] iex> Enum.random 1..100 51 iex> Enum.take_random 1..100, 3 [14, 3, 72]

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iex> String.jaro_distance "helo", "help" 0.8333333333334 String $ mix helo ** (Mix) The task "helo" could not be found. Did you mean "help"?

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# v1.0+ iex> task = Task.async(fn -> ... end) %Task{} iex> Task.await(task, 5_000) # v1.1+ iex> Task.yield(task, 5_000) {:ok, result} | nil iex> Task.shutdown(task, :brutal_kill) {:ok, result} | nil Task

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ExUnit v1.1

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Capture Log # v1.0+ import ExUnit.CaptureIO capture_io fn -> IO.puts "hello" end # v1.1+ import ExUnit.CaptureLog capture_log fn -> Logger.info "hello" end

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# Per test @tag :capture_log test "something with logging" do ... end # Per suite ExUnit.configure capture_log: true Capture Log

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Capture Log 1) test something with logging test/plug/error.exs:59 ** (RuntimeError) oops stacktrace: test/plug/error.exs:59 The following output was logged: 20:27:52.443 [info] log message

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Not implemented tests # @tag :not_implemented test "eventually will do X" $ mix test --exclude not_implemented $ mix test --only not_implemented

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• stacktrace depth is now configurable and has been increased to 20 • More detailed errors • Ability to skip tests • Proper line number in doctests failures More improvements

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Mix v1.1

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mix profile.fprof # CNT ACC (ms) OWN (ms) Total 200279 1972.188 1964.579 Test.run/0 1 1972.166 0.007 Test.do_something/1 3 1972.131 0.040 Test.bottleneck/0 1 1599.490 0.007 ... $ mix profile.fprof my_script.exs

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[build_embedded: Mix.env == :prod, start_permanent: Mix.env == :prod] Closer to releases

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Start Permanent (true) • Shuts the node down if your application crashes

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Build Embedded (false) /_build ├── dev │ └── lib │ ├── cowboy │ │ └── ebin -> ../../../../deps/cowboy/ebin │ ├── cowlib │ │ ├── ebin -> ../../../../deps/cowlib/ebin │ ├── phoenix │ │ ├── ebin │ │ │ ├── Elixir.Access.Phoenix.Socket.beam

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Build embedded (true) • Packages your whole application into _build (no symlinks) • Enables protocol consolidation • No longer automatically compiles

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config/config.exs # v1.0: config/config.exs config :my_app, :key, :value # v1.1: this will warn config :unknown_app, :key, :value

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• "mix compile" tracks only compile-time dependencies for Elixir • "recompile()" inside IEx • Use the safer https protocol instead of git for :github dependencies More improvements

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Deprecations

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Elixir v1.1 # v1.1 iex> "Hello \u2661" "Hello ♡" # v1.0 iex> "Hello \x{2661}” "Hello ♡" SOFT DEPRECATED

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Elixir v1.1 # v1.0 defmodule Calculator do use Behaviour defcallback add(number, number) :: number end SOFT DEPRECATED # v1.1 defmodule Calculator do @callback add(number, number) :: number end

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Elixir v1.1 defmodule Calculator do @typedoc "A complex number" @opaque complex :: ... @doc "Adds two numbers" @callback add(number, number) :: ... end Code.get_docs(Calculator, :type_docs)

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Elixir v1.1 DEPRECATED defimpl Access, for: X do ... end

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Access opts[key] opts[key] opts[key] opts[key] Code Server

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• opts[key] still works • Access defines a subset of the Dict behaviour • The bottleneck does not exist in prod • Common hot-paths have been inlined Access

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Community

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Elixir v1.2

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Migration • Elixir v1.0, v1.1  Support Erlang 17 & 18+  • Elixir v1.2  Supports Erlang 18+

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Erlang 18+ • Variables in maps: %{key => value} • Official support for large maps

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Dicts in Elixir v1.1 • Keyword, Map, HashDict • Unified via the Dict API • Too many options. Often confusing.

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Dicts in Elixir v1.2 • Keyword lists - used as options, allow duplicate keys, user ordered • Maps - pattern matching, fast & scalable, term ordered

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Dict & Set • HashDict will be soft deprecated  Use Map • HashSet will be soft deprecated  Use MapSet • Dict and Set will be soft deprecated

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Multi-aliases alias MyApp.Foo alias MyApp.Bar alias MyApp.Baz alias MyApp.{Foo, Bar, Baz}

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December/2015

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Meanwhile, upgrade to Erlang 18+

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Elixir v1.3

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Collections sink (collectable) widgets |> Enum.filter(fn b -> b.color == :red end) |> Enum.map(fn b -> {b.title, b.height} end) |> Enum.into(%{}) source (enumerable)

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Collections CSV.parse(path) |> Enum.filter(fn b -> b.color == :red end) |> Enum.map(fn b -> {b.title, b.height} end) |> Enum.into(IO.stream(:stdio, :inspect))

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Collections + Laziness CSV.parse(path) |> Stream.filter(fn b -> b.color == :red end) |> Stream.map(fn b -> {b.title, b.height} end) |> Stream.into(IO.stream(:stdio, :inspect)) |> Stream.run()

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Pipeline parallelism CSV.parse(path) |> Stream.async() |> Stream.filter(fn b -> b.color == :red end) |> Stream.map(fn b -> {b.title, b.height} end) |> Stream.into(IO.stream(:stdio, :inspect)) |> Stream.run()

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Pipeline parallelism CSV.parse(path) |> ... |> Stream.async() |> ... |> Stream.async() |> ... |> Stream.async() |> ... |> Stream.run()

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Pipeline parallelism async CSV async async run

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Pipeline parallelism • Each async stage is a process • What happens if one of them crash? • How to provide back-pressure?

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Pipeline parallelism • How to make streams supervised processes? • Pipeline parallelism isn’t even a good strategy

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How to make supervised processes stream data?

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GenRouter

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GenRouter • Connects sources to sinks • Demand-driven

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GenRouter Router

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GenRouter Sink

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GenRouter Source

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GenRouter in | out

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GenRouter GenRouter.start_link( InPart, in_args, OutPart, out_args )

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GenRouter.start_link( GenRouter.SingleIn, [], GenRouter.BroadcastOut, [] ) GenRouter

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SingleIn - BroadcastOut router

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SingleIn - BroadcastOut router 1 1 1 1 1

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SingleIn - BroadcastOut router 1,2 1,2 1,2 1,2 1,2

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SingleIn - BroadcastOut router 1,2,3 1,2,3 1,2,3 1,2,3 1,2,3

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DynamicIn - BroadcastOut router 1,2,3 1,2,3 1,2,3 1,2,3 2 1 3

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DynamicIn - MessageQueueOut router 1 2 3 4 2 1 3

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Some Use Cases • A GenEvent replacement that is process-based • A way to load-balance jobs across a pool of processes

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Demand-driven

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Demand-driven B C A Source | Sink Source | Sink

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Demand-driven B C A Ask 10 Ask 10 Sends max 10 Sends max 10

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Demand-driven • It is a message contract • It pushes back-pressure to the boundary • GenRouter is one impl of this contract • Inspired by Akka Streams

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Supervised TCP Acceptor # Source {:ok, acceptor} = GenRouter.TCPAcceptor.start_link(...) # Sink {:ok, supervisor} = GenRouter.Supervisor.start_link(...) # Source <-> Sink GenRouter.subscribe(supervisor, to: acceptor)

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The path forward • Define the demand-driven message contract • Implement GenRouter and related abstractions • Integrate with streams