[erlang-questions] NIFs and hooking file descriptors to Erlang-manged poll

[Serge Aleynikov]

Thanks Tony for the tip.  I was hoping there is some other way to call the
emulator's internals without resorting to having to implement both a driver
and a NIF library for this purpose.  It seems like it's somewhat an
oversight in the NIF API design that needs to be addressed - there should
be a NIF capable of associating an FD with a callback or else, as you
mentioned, the implementation of this becomes more complicated than
necessary when integrating with external C libraries.

On Thu, Jan 29, 2015 at 9:44 AM, Tony Rogvall <tony@REDACTED> wrote:

> Why not write a small driver that can watch a number of file descriptors,
> Get fd from a nif pass it to the driver_select_driver may be overkill but
> fun.
>
> Could be a useful thing.
>
> I am working on something that may someday be capable of doing this,
> ( https://github.com/tonyrog/niffed )
> It is a a C library that allow you to call (linked) nif library from
> driver code,
> The marshalling code is actually building VM heap compatible data that
> can be processed by the nif code, only by offsetting some pointers :-)
> It is even possible to use the same shared object as both nif and driver!
>
> /Tony
>
> On 29 jan 2015, at 15:20, Serge Aleynikov <serge@REDACTED> wrote:
>
> Is there a way to hook a file descriptor from within a NIF function to the
> select/epoll/poll loop managed by the emulator with a callback invoked in
> the "NIF-land" on activity detected on the file descriptor?
>
> I am looking for similar functionality available to NIF functions that is
> available when writing drivers using driver_select() call (*).  More
> specifically, I have an eventfd file descriptor that I'd like to be
> notified about without allocating a separate OS thread to poll on that FD
> and return results by sending a message to a given Erlang Pid.
>
> Thanks,
>
> Serge
>
> (*) http://www.erlang.org/doc/man/erl_driver.html#driver_select
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