Got error - 1st argument: invalid spec for pid or port, while calling :erlang.trace.

If I turn flame on in LiveDashboard and send a request to my Phoenix app, it printed errors.

>>>pid:#PID<0.1082.0>
>>>tracer:#PID<0.1082.0> alive?:true
>>>self:#PID<0.1087.0> alive?:true process_info:[
  current_function: {Process, :info, 1},
  initial_call: {:proc_lib, :init_p, 5},
  status: :running,
  message_queue_len: 0,
  links: [#PID<0.1085.0>],
  dictionary: [
    "$ancestors": [#PID<0.1085.0>, #PID<0.642.0>, #PID<0.641.0>,
     MyWeb.Endpoint, Owp.Supervisor, #PID<0.475.0>],
    "$meck_call": {:cowboy_handler, :execute},
    "$initial_call": {:cowboy_stream_h, :request_process, 3}
  ],
  trap_exit: false,
  error_handler: :error_handler,
  priority: :normal,
  group_leader: #PID<0.474.0>,
  total_heap_size: 2208,
  heap_size: 1598,
  stack_size: 30,
  reductions: 408,
  garbage_collection: [
    max_heap_size: %{error_logger: true, kill: true, size: 0},
    min_bin_vheap_size: 46422,
    min_heap_size: 233,
    fullsweep_after: 65535,
    minor_gcs: 4
  ],
  suspending: []
]
[error] ** can only have one tracer per process

[error] Ranch protocol #PID<0.1087.0> of listener OwpWeb.Endpoint.HTTP (connection #PID<0.1085.0>, stream id 1) terminated
an exception was raised:
    ** (ArgumentError) errors were found at the given arguments:

  * 1st argument: invalid spec for pid or port

        :erlang.trace(#PID<0.1087.0>, true, [{:tracer, #PID<0.1087.0>}, :call, :return_to, :running, :arity, :timestamp])
        (flame_on 0.7.0) lib/flame_on/capture/mock_function.ex:12: FlameOn.Capture.MockFunction.start_if_not_started/1
        (flame_on 0.7.0) lib/flame_on/capture/mock_function.ex:27: anonymous fn/3 in FlameOn.Capture.MockFunction.generate/3

Added some log to /lib/flame_on/capture/trace.ex.

defmodule FlameOn.Capture.Trace do
  alias FlameOn.Capture.Server

  @flags [:call, :return_to, :running, :arity, :timestamp]
  def start_trace(tracer) do
    IO.puts ">>>tracer:#{inspect(tracer, limit: :infinity, pretty: true)} alive?:#{Process.alive?(tracer)}"
    match_spec = [{:_, [], [{:message, {{:cp, {:caller}}}}]}]
    :erlang.trace_pattern(:on_load, match_spec, [:local])
    :erlang.trace_pattern({:_, :_, :_}, match_spec, [:local])
    IO.puts ">>>self:#{inspect(self(), limit: :infinity, pretty: true)} alive?:#{Process.alive?(self())} process_info:#{inspect(Process.info(self()), limit: :infinity, pretty: true)}"
    :erlang.trace(self(), true, [{:tracer, self()} | @flags])
  end

  def stop_trace do
    :erlang.trace(self(), false, [:all])
    Server.stop_trace()
  end
end

It says that the pid is valid and why does it keep complaining that the first argument is not valid?

DockYard / flame_on

Got error - 1st argument: invalid spec for pid or port, while calling :erlang.trace. #46