2 - State "DRAFT" from [2023-11-05 Sun 22:23]
4 Our core languages are
[[https://www.rust-lang.org/][Rust]] and
[[https://lisp-lang.org/][Lisp]] - this is the killer combo which will allow NAS-T
5 to rapidly develop high-quality software. As such, it's crucial that these two very
6 different languages (i.e. compilers) are able to interoperate seamlessly.
8 Some interop methods are easy to accomodate via the OS - such as IPC or data sharing,
9 but others are a bit more difficult.
11 In this 2-part series we'll build a FFI bridge between Rust and Lisp, which is something
12 that
/can/ be difficult, due to some complications with Rust and because this is not the
13 most popular software stack (yet ;). This is an experiment and may not make it to our
14 code-base, but it's definitely something worth adding to the toolbox in case we need it.
17 The level of interop we're after in this case is
[[https://en.wikipedia.org/wiki/Foreign_function_interface][FFI]].
19 Basically, calling Rust code from Lisp and vice-versa. There's an article about calling
20 Rust from Common Lisp
[[https://dev.to/veer66/calling-rust-from-common-lisp-45c5][here]] which shows the basics and serves as a great starting point
23 The complication(s) with Rust I mentioned early is really just that
/it is not C/.
=C= 24 is old, i.e. well-supported with a stable ABI, making the process of creating bindings
25 for a C library a breeze in many languages.
27 For a Rust library we need to first appease the compiler, as explained in
[[https://doc.rust-lang.org/nomicon/ffi.html#calling-rust-code-from-c][this section]] 28 of the Rustonomicon. Among other things it involves changing the calling-convention of
29 functions with a type signature and editing the Cargo.toml file to produce a
30 C-compatible ABI binary. The Rust default ABI is unstable and can't reliably be used
34 Using FFI involves some overhead. Check
[[https://github.com/dyu/ffi-overhead][here]] for an example benchmark across a few
35 languages. While building the NAS-T core, I'm very much aware of this, and will need a
36 few sanity benchmarks to make sure the cost doesn't outweigh the benefit. In particular,
37 I'm concerned about crossing multiple language barriers (Rust
<->C
<->Lisp).
41 For starters, I'm going to assume we all have Rust (via
=rustup=) and Lisp (
=sbcl= only)
42 installed on our GNU/Linux system (some tweaks needed for Darwin/Windows, not covered in
45 Create a new library crate. For this example we're focusing on a 'skeleton' for
46 /dynamic/ libraries only, so our experiment will be called
=dylib-skel= or
*dysk* for
48 src_sh[:exports code]{cargo init dysk --lib && cd dysk}
50 A
=src/lib.rs= will be generated for you. Go ahead and delete that. We're going to be
51 making our own
=lib.rs= file directly in the root directory (just to be cool).
53 The next step is to edit your
=Cargo.toml= file. Add these lines after the
=[package]= 54 section and before
=[dependencies]=:
57 crate-type = ["cdylib","rlib"]
64 This tells Rust to generate a shared C-compatible object with a
=.so= extension which we
65 can open using
[[https://man.archlinux.org/man/dlopen.3.en][dlopen]].
68 Next, we want the
=cbindgen= program which we'll use to generate header files for
69 C/C++. This step isn't necessary at all, we just want it for further experimentation.
71 src_sh[:exports code]{cargo install --force cbindgen}
73 We append the
=cbindgen= crate as a
/build dependency/ to our
=Cargo.toml= like so:
79 #+begin_src conf-toml :tangle cbindgen.toml 81 autogen_warning = "/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */"
82 include_version = true
85 after_includes = "#define DYSK_VERSION \"0.1.0\""
89 documentation_style = "c99"
90 usize_is_size_t = true
95 #+begin_src rust :tangle build.rs 96 fn main() -> Result<(), cbindgen::Error> {
97 if let Ok(b) = cbindgen::generate(std::env::var("CARGO_MANIFEST_DIR").unwrap()) {
98 b.write_to_file("dysk.h"); Ok(())}
99 else { panic!("failed to generate dysk.h from cbindgen.toml") } }
102 #+begin_src rust :tangle lib.rs 103 //! lib.rs --- dysk library
104 use std::ffi::{c_char, c_int, CString};
106 pub extern "C" fn dysk_hello() -> *const c_char {
107 CString::new("hello from rust").unwrap().into_raw()}
109 pub extern "C" fn dysk_plus(a:c_int,b:c_int) -> c_int {a+b}
111 pub extern "C" fn dysk_plus1(n:c_int) -> c_int {n+1}
114 #+begin_src rust :tangle test.rs 115 //! test.rs --- dysk test
116 fn main() { let mut i = 0u32; while i < 500000000 {i+=1; dysk::dysk_plus1(2 as core::ffi::c_int);}}
120 cargo build --release
123 #+begin_src lisp :tangle dysk.lisp 124 (load-shared-object #P"target/release/libdysk.so")
125 (define-alien-routine dysk-hello c-string)
126 (define-alien-routine dysk-plus int (a int) (b int))
127 (define-alien-routine dysk-plus1 int (n int))
128 (dysk-hello) ;; => "hello from rust"
132 time target/release/dysk-test
134 #+begin_src lisp :tangle test.lisp 135 (time (dotimes (_ 500000000) (dysk-plus1 2)))