nimforum mirror - Using Shared Libraries written in Nim via FFI

b6d (orginal) [2019-01-24T19:49:03+01:00] view original

Hello Nim community,

I'm enjoying Nim a great deal, but coming from a scripting language background, I'm having trouble figuring out some compiling-and-dynamic-linking-and-memory-related things on my own. Maybe you can help me?

I have a Linux system, on which I've written a simple library in Nim:

# mylib.nim
func fib*(a: cint): cint {.exportc, cdecl, dynlib.} =
  if a <= 0: 0 elif a == 1: 1 else: fib(a - 1) + fib(a - 2)

I compile this library like so:

nim compile --define:release --app:lib --noMain --out:mylib.so mylib.nim

Because of reasons, I'd like to call functions in this library from within Perl 5.

Perl lets me use shared libraries via libffi (Perl Package FFI::Platypus), and the following seems to work:

# myprog.pl
use FFI::Platypus;
my $ffi = FFI::Platypus->new(lib=>'./mylib.so');
my $fib = $ffi->function(fib=>['int'] => 'int');
print $fib->call(10);  # prints 55

However, based on my understanding of Nim's documentation I highly doubt that this will work in nontrivial situations, and I lack the skills to debug memory leaks and segfaults.

I'm wondering:

Do I have to call NimMain() first when interfacing with a shared library written in Nim?

If yes, do I have to compile and load nimrtl and call nimrtl.NimMain() when interfacing with more than one shared library written in Nim?

Do I have to protect strings returned by Nim functions from the Garbage Collector (by copying them before the GC can get them)?

Are there any other pitfalls I should be aware of?

Kind regards,

Bernhard

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