[erlang-questions] erl_driver vs NIF

Lukas Larsson <>
Wed Dec 7 09:57:48 CET 2016


Hello,

On Tue, Dec 6, 2016 at 9:56 PM, Caragea Silviu <> wrote:

>
> From what I know the NIF is the fastest way to call c/c++ code from
> erlang. The disadvantage is that you need to return in under 1 ms in order
> to make sure the schedulers are not affected.
>
> using erl_driver and  port_control is not the same ? because based on the
> documentation this is a sync call that blocks scheduler until the native
> method returns.
>

The same ~1 ms limit exists for port callbacks as nif function calls.

For some reason there is a rumor circling around that you somehow
circumvent the limit if you convert your nif code to a linked-in driver.
This is not the case. The only thing you do by converting the code from a
nif to linked-in driver is gain access to more tools to partitions the work
(mostly driver_select[1], but also some other things like the async thread
pool), and you possibly make some of the problems that long running native
code can cause less likely.

Lukas

1: Soon this limit will be removed by the inclusion of enif_select,
https://github.com/erlang/otp/pull/1264
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