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lib/livebook/runtime/erl_dist/io_forward_gl.ex
defmodule Livebook.Runtime.ErlDist.IOForwardGL do
# An IO device process forwarding all requests to sender's group
# leader.
#
# We register this device as the `:standard_error` in the runtime
# node, so that all evaluation warnings are treated as stdout.
#
# The process implements [The Erlang I/O Protocol](https://erlang.org/doc/apps/stdlib/io_protocol.html)
# and can be thought of as a virtual IO device.
use GenServer
@doc """
Starts the IO device.
## Options
* `:name` - the name to register the process under. Optional.
If the name is already used, it will be unregistered before
starting the process and registered back when the server
terminates
"""
@spec start_link(keyword()) :: GenServer.on_start()
def start_link(opts \\ []) do
name = opts[:name]
if previous = name && Process.whereis(name) do
Process.unregister(name)
end
GenServer.start_link(__MODULE__, {name, previous}, opts)
end
@impl true
def init({name, previous}) do
Process.flag(:trap_exit, true)
{:ok, %{name: name, previous: previous}}
end
@impl true
def handle_info({:io_request, from, reply_as, req}, state) do
case Process.info(from, :group_leader) do
{:group_leader, group_leader} ->
# Forward the request to sender's group leader and instruct
# it to get back to the sender.
send(group_leader, {:io_request, from, reply_as, req})
_ ->
send(from, {:io_reply, reply_as, {:error, :terminated}})
end
{:noreply, state}
end
@impl true
def terminate(_, %{name: name, previous: previous}) do
if name && previous do
Process.unregister(name)
Process.register(previous, name)
end
:ok
end
end