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    NIFs are rad. I know they’re often used for performance reasons but I really like them for exposing specific libs, or OS SDK functions (e.g. Core* stuff on MacOS) to Erlang code. NIF/BEAM provides a mechanism for keeping data around on the C side and a “reference” type that lets you wrap & return a C pointer and pass it around in your Erlang code, so that can be super nice - you can do all the allocation/release nitty-gritty neatly in your C code, and leave yourself free to just think about the application structure & flow in Erlang, which for me is one of the areas where it really shines. Also NIF provides a lot of “interface”-style stuff that (AFAICT) ports just don’t - when asking about interfacing with C code, Erlang people often say “just write a port and communicate over stdin/out”, which is great, but then you basically have to define your own comms mechanisms - whereas with NIF it’s just a function call and all the necessary methods for converting types are included.

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      Oh, maybe you (or some other lobster!) can help me with a thing. To the best of my knowledge, Erlang (and hence Elixir) use bignums for integers…unfortunately, the docs don’t say anything about how to get that across over in C land. Any ideas?

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        It doesn’t appear as though the NIF interface gives you an easy way to get Erlang bignums into your NIF. The icky way to pass in a bigint might be to encode it as a binary or string and decode it in the NIF. If you’re interested, you could take a peek at big.c and big.h. There are functions big_to_bytes, which should return an array of digits, and big_to_double, which should return a double (if the bignum fits).

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          Sounds right. I’ve not had to share numbers bigger than 64-bit ints so I’ve just used enif_get_int64 (or enif_get_long, enif_get_uint64 etc) to do the conversion (and relevant enif_make_* the other way), and haven’t had any issues with that.

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            Does that work in C ports?

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              I don’t think so. I think you want to use ei functions like ei_encode_* and ei_decode_* for that.

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                Aha, sure enough:

                int ei_decode_bignum(const char *buf, int *index, mpz_t obj) Decodes an integer in the binary format to a GMP mpz_t integer. To use this function, the ei library must be configured and compiled to use the GMP library.

                Thanks for the direction.

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      Erlang is a safe, functional language with high reliability. The NIF’s can boost performance but break safety or other properties. This looks like a good, use case for one of the safe, systems languages we have now. The code still stays safe even when breaking Erlang model a bit for performance. There might even be a way to use advanced features to encode whatever structure is necessary to get them to play nice with the scheduler. That part is purely speculative, though.

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        You might be interested to know that Rustler supports annotating Rust NIFs as dirty NIFs :)

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          That’s great! Exactly the kind of thing I was thinking of.

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        NIFs are extremely useful, but they’re also a foot-gun with a hair trigger. In addition to being able to take down your Erlang node from a faulty NIF call, calling long-running NIFs (where long-running usually means >1ms) can have degenerate effects on VM performance.

        Erlang scheduler threads are written to rapidly switch out Erlang processes and communicate with one another. When a scheduler runs a long-running NIF, that scheduler is no longer able to communicate with the other scheduler threads until the NIF finishes running. You can play around with this to get a better feel of how NIFs can misbehave and have large effects on the BEAM.

        Please don’t take this as discouraging writing NIFs, though! If you are considering writing a NIF, please read this carefully. It will save you a lot of pain and misery down the road.

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          If memory serves, Erlang recently added better support for helping NIFs play nice with the scheduler. I haven’t had occasion to use that, though, since if I’m writing C I want it in a port for stability anyways. :)