Mercurial > org > blog / draft/dylib-skel.org

 #+title: Shared Library Skeletons
 * Overview
 :PROPERTIES:
 :ID:       748ba6e4-60db-4ff7-9d78-12c3f67644d8
 :END:
 + CODE :: [[https://lab.rwest.io/packy/stash/dysk][packy/stash/dysk]]
 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
 to rapidly develop high-quality software. As such, it's crucial that these two very
 different languages (i.e. compilers) are able to interoperate seamlessly.
 
 Some interop methods are easy to accomodate via the OS - such as IPC or data sharing,
 but others are a bit more difficult.
 
 In this 2-part series we'll build a FFI bridge between Rust and Lisp, which is something
 that /can/ be difficult, due to some complications with Rust and because this is not the
 most popular software stack (yet ;). This is an experiment and may not make it to our
 code-base, but it's definitely something worth adding to the toolbox in case we need it.
 ** FFI
 :PROPERTIES:
 :ID:       0e490b3b-0c15-4963-9d43-7d2a689ec371
 :END:
 The level of interop we're after in this case is [[https://en.wikipedia.org/wiki/Foreign_function_interface][FFI]].
 
 Basically, calling Rust code from Lisp and vice-versa. There's an article about calling
 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
 for those interested.
 *** Rust ABI
 :PROPERTIES:
 :ID:       6c24dc95-eea6-44fb-8c7f-bb49227ca7bf
 :END:
 The complication(s) with Rust I mentioned early is really just that /it is not C/. =C=
 is old, i.e. well-supported with a stable ABI, making the process of creating bindings
 for a C library a breeze in many languages.
 
 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]]
 of the Rustonomicon. Among other things it involves changing the calling-convention of
 functions with a type signature and editing the Cargo.toml file to produce a
 C-compatible ABI binary. The Rust default ABI is unstable and can't reliably be used
 like the C ABI can.
 
 [[https://github.com/rodrimati1992/abi_stable_crates][abi_stable_crates]] is a project which addresses some of the ABI concerns, presenting a
 sort of ABI-API as a Rust library. Perhaps this is the direction the ecosystem will go
 with in order to maintain an unstable ABI, but for now there is no 'clear' pathway for a
 friction-less FFI development experience in Rust.
 
 *** Overhead
 :PROPERTIES:
 :ID:       faf8fbcb-3403-4e2f-b881-ef1404ad9780
 :END:
 Using FFI involves some overhead. Check [[https://github.com/dyu/ffi-overhead][here]] for an example benchmark across a few
 languages. While building the NAS-T core, I'm very much aware of this, and will need a
 few sanity benchmarks to make sure the cost doesn't outweigh the benefit. In particular,
 I'm concerned about crossing multiple language barriers (Rust<->C<->Lisp).
 
 * basic example
 :PROPERTIES:
 :ID:       ab04fff7-51c9-4f1c-b61b-fa4739932343
 :END:
 ** Setup
 :PROPERTIES:
 :ID:       08420b18-3856-4b62-9523-98fb3398afca
 :END:
 For starters, I'm going to assume we all have Rust (via [[https://rustup.rs/][rustup]]) and Lisp ([[https://www.sbcl.org/][sbcl]] only)
 installed on our GNU/Linux system (some tweaks needed for Darwin/Windows, not covered in
 this post).
 *** Cargo
 :PROPERTIES:
 :ID:       cfeb1299-67c5-4a64-863e-f214e195e176
 :END:
 Create a new library crate. For this example we're focusing on a 'skeleton' for
 /dynamic/ libraries only, so our experiment will be called =dylib-skel= or *dysk* for
 short.
 src_sh[:exports code]{cargo init dysk --lib && cd dysk} 
 
 A =src/lib.rs= will be generated for you. Go ahead and delete that. We're going to be
 making our own =lib.rs= file directly in the root directory (just to be cool).
 
 The next step is to edit your =Cargo.toml= file. Add these lines after the =[package]=
 section and before =[dependencies]=:
 #+begin_src conf-toml
 [lib]
 crate-type = ["cdylib","rlib"]
 path = "lib.rs"
 [[bin]]
 name="dysk-test"
 path="test.rs"
 #+end_src
 
 This tells Rust to generate a shared C-compatible object with a =.so= extension which we
 can open using [[https://man.archlinux.org/man/dlopen.3.en][dlopen]].
 *** cbindgen
 :PROPERTIES:
 :ID:       435d84d6-c959-4bf6-ad37-fb6e524b54ff
 :END:
 **** install
 :PROPERTIES:
 :ID:       15115ab8-e7b4-4050-9567-bf026cc140d1
 :END:
 Next, we want the =cbindgen= program which we'll use to generate header files for
 C/C++. This step isn't necessary at all, we just want it for further experimentation.
 
 src_sh[:exports code]{cargo install --force cbindgen}
 
 We append the =cbindgen= crate as a /build dependency/ to our =Cargo.toml= like so:
 #+begin_src conf-toml
 [build-dependencies]
 cbindgen = "0.24"
 #+end_src
 **** cbindgen.toml
 :PROPERTIES:
 :ID:       21d776b7-9f8d-445c-83c2-8e0c28751827
 :END:
 #+begin_src conf-toml :tangle cbindgen.toml
 language = "C"
 autogen_warning = "/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */"
 include_version = true
 namespace = "dysk"
 cpp_compat = true
 after_includes = "#define DYSK_VERSION \"0.1.0\""
 line_length = 88
 tab_width = 2
 documentation = true
 documentation_style = "c99"
 usize_is_size_t = true
 [cython]
 header = "dysk.h"
 #+end_src
 **** build.rs
 :PROPERTIES:
 :ID:       469dd142-bafa-4076-8ba9-baf088e60260
 :END:
 #+begin_src rust :tangle build.rs
 fn main() -> Result<(), cbindgen::Error> {
   if let Ok(b) = cbindgen::generate(std::env::var("CARGO_MANIFEST_DIR").unwrap()) {
     b.write_to_file("dysk.h"); Ok(())}
   else { panic!("failed to generate dysk.h from cbindgen.toml") } }
 #+end_src
 ** lib.rs
 :PROPERTIES:
 :ID:       e9d50e77-4d1e-4d38-90aa-9977d8c6c888
 :END:
 #+begin_src rust :tangle lib.rs
 //! lib.rs --- dysk library
 use std::ffi::{c_char, c_int, CString};
 #[no_mangle]
 pub extern "C" fn hello() -> *const c_char {
   CString::new("hello from rust").unwrap().into_raw()}
 #[no_mangle]
 pub extern "C" fn plus(a:c_int,b:c_int) -> c_int {a+b}
 #[no_mangle]
 pub extern "C" fn plus1(n:c_int) -> c_int {n+1}
 #+end_src
 ** test.rs
 :PROPERTIES:
 :ID:       84b5dffe-7171-4d72-9788-f288e3185070
 :END:
 #+begin_src rust :tangle test.rs
 //! test.rs --- dysk test
 fn main() { let mut i = 0u32; while i < 500000000 {i+=1; dysk::plus1(2 as core::ffi::c_int);}}
 #+end_src
 ** compile
 :PROPERTIES:
 :ID:       30f4fb3e-0757-4df6-947f-8d1e11edabf9
 :END:
 #+begin_src sh
 cargo build --release
 #+end_src
 ** load from SBCL
 :PROPERTIES:
 :ID:       69b517f2-648d-4e44-b956-7879b3dadf99
 :END:
 #+begin_src lisp :tangle dysk.lisp
 ;;; dysk.lisp
 ;; (dysk:hello) ;; => "hello from rust"
 (defpackage :dysk
   (:use :cl :sb-alien)
   (:export :hello :plus :plus1))
 (in-package :dysk)
 (load-shared-object #P"target/release/libdysk.so")
 (define-alien-routine hello c-string)
 (define-alien-routine plus int (a int) (b int))
 (define-alien-routine plus1 int (n int))
 #+end_src
 ** benchmark
 :PROPERTIES:
 :ID:       86e4195d-601b-4736-b852-1209a6d38bdf
 :END:
 #+begin_src shell
 time target/release/dysk-test
 #+end_src
 #+begin_src lisp :tangle test.lisp
 (time (dotimes (_ 500000000) (dysk:plus1 2)))
 #+end_src