[erlang-questions] erl_ddll:load_driver behaviour.

Amit Kapoor <>
Tue Dec 11 00:46:40 CET 2012

Hi folks,

Trying to understand load_drive behaviour. The test code I am using is at the
end of this email. The driver being loaded is a dummy driver with a printf
message in the DRIVER_INIT code. If I call spawn:test(true,3), the printf
message in DRIVER_INIT code gets displayed 3 times, whereas spawn:test(false,3)
displays the same message only once. The erl_ddll manual is a bit lacking in
this area, so wanted to get some clarification.

1. Is this the expected behaviour?
2. Child processes seem to 'inherit' drivers loaded by parent process?





-export([test/2, load_driver/0]).

test(_, 0) ->
test(Spawn, Count) ->
  case Spawn of
    true -> spawn(fun() -> load_driver() end);
    false -> load_driver()
  test(Spawn, Count - 1).

load_driver() ->
  case erl_ddll:load_driver("/home/user", test_drv) of
    ok -> ok;
    {error, already_loaded} -> ok

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