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Open Telecom Platform (OTP)

Patterns (behaviors) for structuring programs.

Elixir-lang.org -> Getting Started -> Building OTP Applications with Mix

Holding state

Supervisor Tree

Supervisors = Monitor workers / restart worker when bad things happen

Workers = Doers

Supervisor Tree

Behaviors

Contractual callbacks specific to your application.

  • Supervisor
  • GenServer
  • GenFSM
  • GenEvent
  • Application

Supervisor.Behavior

Strategies

  • one_for_one 1 failure = 1 restart
  • one_for_all 1 failure = all restart
  • rest_for_one 1 failure = all restart

GenServer.Behavior

init(initial_state)

handle_cast Asyncronous fire and forget call

handle_call Syncronous call that (usually) implies a return value.

start_link Called by the supervisor to get things running and return a pid for it to monitor

Running

Locally

iex -S mix

:gen_server.call(:counter, :stat)
#> 0

:gen_server.cast(:counter, :increment)
:gen_server.cast(:counter, :increment)

:gen_server.call(:counter, :stat)
#> 2

# worker blows up
:gen_server.cast(:counter, :boom)

:gen_server.call(:counter, :stat)
#> 0

Distributed

Note: Erlang/Elixir communicates over port 4369 by default. On locked down networks like public wifi run epmd -port 80 -daemon to tell Erlang/Elixir to communicate over port 80.

# Start our host
mix --name stack@<ip> --cookie foo

# Start client
iex --name lastname@<ip> foo --cookie bar

Node.connect :"stack@<ip>"
#> true

:gen_server.cast( {:global, :counter}, :increment )

:gen_server.call( {:global, :counter}, :stat )