Angel's Blog

Elixir: Making Concurrent API Calls

Angel — Sat, 13 Apr 2024 02:47:12 GMT

angelcool@fedora-laptop$
angelcool@fedora-laptop$date
Fri Apr 12 07:51:16 PM PDT 2024
angelcool@fedora-laptop$ls lib/
coolprogram.ex  coordinator.ex  worker.ex
angelcool@fedora-laptop$cat lib/coolprogram.ex 
defmodule CoolProgram do
  def temperature_of(cities) do
    coordinator_pid = spawn(CoolProgram.Coordinator, :loop, [[], Enum.count(cities)])
    cities |> Enum.each(fn city ->
        worker_pid = spawn(CoolProgram.Worker, :loop, [])
        send(worker_pid, {coordinator_pid, city})
    end)
  end
end
angelcool@fedora-laptop$cat lib/coordinator.ex 
defmodule CoolProgram.Coordinator do

  def loop(results \\ [], results_expected) do
    receive do
      {:ok, result} ->
        new_results = [result|results]
        if results_expected == Enum.count(new_results) do
          send(self(), :exit)
        end
        loop(new_results, results_expected)
      :exit ->
          IO.puts(results |> Enum.sort |> Enum.join(", "))
        _->
          loop(results, results_expected)
    end
  end

end
angelcool@fedora-laptop$cat lib/worker.ex 
defmodule CoolProgram.Worker do

  def temperature_of(location) do
    result = url_for(location)
      |> HTTPoison.get
      |> parse_response
    case result do
      {:ok, temp} ->
        "#{location}: #{temp}° C"
      :error ->
        "#{location} not found"
    end
  end

  defp url_for(location) do
    location = URI.encode(location)
    "http://api.openweathermap.org/data/2.5/weather?q=#{location}&appid=#{apikey()}"
  end

  defp parse_response({:ok, %HTTPoison.Response{body: body, status_code: 200}}) do
    body
      |> JSON.decode!
      |> compute_temperature()
  end

  defp parse_response(_) do
    :error
  end

  defp compute_temperature(json) do
    try do
      temp = (json["main"]["temp"]-273.15)
        |> Float.round(1)
      {:ok, temp}
    rescue
      _-> :error
    end
  end

  defp apikey do
    "XXXXXXXXXXXXXXXXXXXXXXXXXXXX"
  end

  def loop do
    receive do
      {sender_pid, location}->
        send(sender_pid, {:ok, temperature_of(location)})
      _->
        IO.puts "don't know how to process this message"
    end
    loop()
  end
end
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$iex -S mix
Compiling 1 file (.ex)
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> cities=["San Diego", "Merida", "Singapore", "Los Angeles", "Mexico City", "Miami", "Temecula", "Buenos Aires", "Ojai" ]
["San Diego", "Merida", "Singapore", "Los Angeles", "Mexico City", "Miami",
 "Temecula", "Buenos Aires", "Ojai"]
iex(2)> CoolProgram.temperature_of(cities)
:ok
Buenos Aires: 17.0° C, Los Angeles: 14.7° C, Merida: 25.0° C, Mexico City: 22.8° C, Miami: 22.0° C, Ojai: 14.2° C, San Diego: 15.2° C, Singapore: 30.8° C, Temecula: 13.1° C
iex(3)>

Elixir: Miscellaneous Notes

Angel — Fri, 12 Apr 2024 19:00:02 GMT

# Filtering files in a directory by filename
angelcool@fedora-laptop$date
Fri Apr 12 12:02:42 PM PDT 2024
angelcool@fedora-laptop$iex
...
iex(90)> "/home/angelcool/Downloads" \
...(90)> |> Path.join("**/*.rpm") \
...(90)> |> Path.wildcard \
...(90)> |> Enum.filter(fn fname -> String.contains?(Path.basename(fname),"dbeaver") end)
["/home/angelcool/Downloads/dbeaver-ce-24.0.2-stable.x86_64.rpm"]

# Making an HTTP GET request
iex(18)> :inets.start()
:ok
iex(19)> :ssl.start()
:ok
iex(20)> :httpc.request(:get, {'https://www.angelcool.net', []}, [ssl: :httpc.ssl_verify_host_options(true)], [])
...

Elixir: Clustering Elixir Nodes - Updating Shared State.

Angel — Sat, 06 Apr 2024 18:47:27 GMT


angelcool@fedora-laptop$ # Let's get the date and versions used
angelcool@fedora-laptop$date
Sat Apr  6 11:51:08 AM PDT 2024
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$mix --version
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Mix 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$mix phx.new --version
Phoenix installer v1.7.11
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$ # The gist of this post...
angelcool@fedora-laptop$
angelcool@fedora-laptop$ # Terminal 1
angelcool@fedora-laptop$ iex --name a@127.0.0.1
iex(a@127.0.0.1)1>

angelcool@fedora-laptop$ #Terminal 2
angelcool@fedora-laptop$ iex --name b@127.0.0.1
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(b@127.0.0.1)1> Node.connect :"a@127.0.0.1"
true
iex(b@127.0.0.1)2> Node.list
[:"a@127.0.0.1"]
iex(b@127.0.0.1)3>

# Terminal 1
iex(a@127.0.0.1)> Agent.start(
  fn -> %{hello: "world"} end, 
  name: {:global, GlobalAgent}
)
{:ok, #PID<0.116.0>} 

# Terminal 2
iex(b@127.0.0.1)4> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "world"}

# Terminal 2 - Update state
iex(b@127.0.0.1)5> Agent.update {:global, GlobalAgent}, fn _ -> %{hello: "everyone!"}  end
:ok
iex(b@127.0.0.1)6>

# Terminal 2 - Get new state
iex(b@127.0.0.1)6> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "everyone!"}

# Terminal 1 - Get new state
iex(a@127.0.0.1)2> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "everyone!"}

Elixir: Processes Talking Amongst Themselves

Angel — Tue, 02 Apr 2024 18:41:03 GMT

angelcool@fedora-laptop$date
Tue Apr  2 11:31:57 AM PDT 2024
angelcool@fedora-laptop$mix new process-demo --app process_a
* creating README.md
* creating .formatter.exs
* creating .gitignore
* creating mix.exs
* creating lib
* creating lib/process_a.ex
* creating test
* creating test/test_helper.exs
* creating test/process_a_test.exs

Your Mix project was created successfully.
You can use "mix" to compile it, test it, and more:

    cd process-demo
    mix test

Run "mix help" for more commands.
angelcool@fedora-laptop$
angelcool@fedora-laptop$cd process-demo/
angelcool@fedora-laptop$ls -l
total 8
drwxr-xr-x. 1 angelcool angelcool  24 Apr  2 11:31 lib
-rw-r--r--. 1 angelcool angelcool 575 Apr  2 11:31 mix.exs
-rw-r--r--. 1 angelcool angelcool 476 Apr  2 11:31 README.md
drwxr-xr-x. 1 angelcool angelcool  66 Apr  2 11:31 test
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat lib/process_a.ex 
defmodule ProcessA do
  def receiverA(count) do
    receive do
      {from, message} -> send(from, {"Greetings from ProcessA!.", message})
      receiverA(count+1)
    end
  end
end
angelcool@fedora-laptop$cat lib/process_b.ex 
defmodule ProcessB do
  def initialize do
    pid_A = spawn(ProcessA, :receiverA, [1])
    recieverB(pid_A)
  end

  def recieverB(pid_A) do
    receive do
      {message} ->
        send(pid_A, {self(), message})
        recieverB(pid_A)
      {response, originalmessage} ->
        IO.puts("Response: #{response}")
        IO.puts("Original Message: #{originalmessage}")
        recieverB(pid_A)
    end
  end
end
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$
angelcool@fedora-laptop$mix phx.new --version
Phoenix installer v1.7.11
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex -S mix
Compiling 2 files (.ex)
Generated process_a app
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> pid_B = spawn(ProcessB, :initialize, [])
#PID<0.166.0>
iex(2)> send(pid_B, {"Hi! This is a message from process B!"})
Response: Greetings from ProcessA!.
{"Hi! This is a message from process B!"}
Original Message: Hi! This is a message from process B!
iex(3)>