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nerves_runtime

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Small, general runtime utilities for Nerves devices

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nerves_runtime lib nerves_runtime power.ex
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lib/nerves_runtime/power.ex 

defmodule Nerves.Runtime.Power do

  @moduledoc false



  # This GenServer handles the poweroff and reboot operations:

  #

  # 1. It serializes calls to reboot and poweroff. First one wins if

  #    multiple processes want reboot simultaneously.

  # 2. It decouples the process that the reboot or poweroff sequence

  #    happens in. This lets supervision trees go down midway through

  #    the poweroff process without killing the process doing the

  #    poweroff.



  use GenServer

  require Logger



  @spec start_link(keyword()) :: GenServer.on_start()

  def start_link(options) do

    GenServer.start_link(__MODULE__, options, name: __MODULE__)

  end



  @doc """

  Run a power management command



  The only valid commands are `"reboot"`, `"poweroff"`, and `"halt"`. This is

  NOT intended to be called directly. Call `Nerves.Runtime.reboot/0`, etc. instead.



  This function doesn't return since the system will power off or reboot

  shortly after it's called.

  """

  @spec run_command(String.t()) :: no_return()

  def run_command(cmd) when is_binary(cmd) do

    GenServer.cast(__MODULE__, cmd)



    # Sleep forever since callers of this function don't expect it to return

    Process.sleep(:infinity)

  end



  @impl GenServer

  def init(_options) do

    {:ok, nil}

  end



  @impl GenServer

  @dialyzer {:nowarn_function, handle_cast: 2}

  def handle_cast(cmd, _state) do

    Logger.info("#{__MODULE__} : device told to #{cmd}")



    # Invoke the appropriate command to tell erlinit that a shutdown of the

    # Erlang VM is imminent. Once this returns, the Erlang has about 10

    # seconds to exit unless `--graceful-powerdown` is used in the

    # `erlinit.config` to modify the timeout.

    {_, 0} = Nerves.Runtime.cmd(cmd, [], :info)



    # Start a graceful shutdown

    :ok = :init.stop()

    {:stop, :normal}

  after

    # If anything unexpected happens, call :erlang.halt() to avoid getting

    # stuck in a state where the application thinks it's done.

    :erlang.halt()

    {:stop, :normal}

  end

end