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#+title: Shared Library Skeletons |
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* Overview |
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+ CODE :: [[https://lab.rwest.io/packy/stash/dysk][packy/stash/dysk]] |
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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 |
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to rapidly develop high-quality software. As such, it's crucial that these two very |
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different languages (i.e. compilers) are able to interoperate seamlessly. |
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Some interop methods are easy to accomodate via the OS - such as IPC or data sharing, |
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but others are a bit more difficult. |
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In this 2-part series we'll build a FFI bridge between Rust and Lisp, which is something |
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that /can/ be difficult, due to some complications with Rust and because this is not the |
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most popular software stack (yet ;). This is an experiment and may not make it to our |
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code-base, but it's definitely something worth adding to the toolbox in case we need it. |
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** FFI |
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The level of interop we're after in this case is [[https://en.wikipedia.org/wiki/Foreign_function_interface][FFI]]. |
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Basically, calling Rust code from Lisp and vice-versa. There's an article about calling |
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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 |
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for those interested. |
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*** Rust ABI |
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The complication(s) with Rust I mentioned early is really just that /it is not C/. =C= |
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is old, i.e. well-supported with a stable ABI, making the process of creating bindings |
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for a C library a breeze in many languages. |
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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]] |
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of the Rustonomicon. Among other things it involves changing the calling-convention of |
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functions with a type signature and editing the Cargo.toml file to produce a |
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C-compatible ABI binary. The Rust default ABI is unstable and can't reliably be used |
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like the C ABI can. |
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[[https://github.com/rodrimati1992/abi_stable_crates][abi_stable_crates]] is a project which addresses some of the ABI concerns, presenting a |
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sort of ABI-API as a Rust library. Perhaps this is the direction the ecosystem will go |
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with in order to maintain an unstable ABI, but for now there is no 'clear' pathway for a |
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friction-less FFI development experience in Rust. |
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*** Overhead |
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Using FFI involves some overhead. Check [[https://github.com/dyu/ffi-overhead][here]] for an example benchmark across a few |
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languages. While building the NAS-T core, I'm very much aware of this, and will need a |
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few sanity benchmarks to make sure the cost doesn't outweigh the benefit. In particular, |
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I'm concerned about crossing multiple language barriers (Rust<->C<->Lisp). |
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* basic example |
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** Setup |
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For starters, I'm going to assume we all have Rust (via [[https://rustup.rs/][rustup]]) and Lisp ([[https://www.sbcl.org/][sbcl]] only) |
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installed on our GNU/Linux system (some tweaks needed for Darwin/Windows, not covered in |
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this post). |
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*** Cargo |
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Create a new library crate. For this example we're focusing on a 'skeleton' for |
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/dynamic/ libraries only, so our experiment will be called =dylib-skel= or *dysk* for |
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short. |
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src_sh[:exports code]{cargo init dysk --lib && cd dysk} |
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A =src/lib.rs= will be generated for you. Go ahead and delete that. We're going to be |
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making our own =lib.rs= file directly in the root directory (just to be cool). |
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The next step is to edit your =Cargo.toml= file. Add these lines after the =[package]= |
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section and before =[dependencies]=: |
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#+begin_src conf-toml |
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[lib] |
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crate-type = ["cdylib","rlib"] |
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path = "lib.rs" |
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[[bin]] |
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name="dysk-test" |
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path="test.rs" |
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#+end_src |
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This tells Rust to generate a shared C-compatible object with a =.so= extension which we |
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can open using [[https://man.archlinux.org/man/dlopen.3.en][dlopen]]. |
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*** cbindgen |
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**** install |
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Next, we want the =cbindgen= program which we'll use to generate header files for |
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C/C++. This step isn't necessary at all, we just want it for further experimentation. |
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src_sh[:exports code]{cargo install --force cbindgen} |
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We append the =cbindgen= crate as a /build dependency/ to our =Cargo.toml= like so: |
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#+begin_src conf-toml |
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[build-dependencies] |
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cbindgen = "0.24" |
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#+end_src |
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**** cbindgen.toml |
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#+begin_src conf-toml :tangle cbindgen.toml |
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language = "C" |
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autogen_warning = "/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */" |
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include_version = true |
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namespace = "dysk" |
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cpp_compat = true |
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after_includes = "#define DYSK_VERSION \"0.1.0\"" |
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line_length = 88 |
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tab_width = 2 |
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documentation = true |
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documentation_style = "c99" |
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usize_is_size_t = true |
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[cython] |
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header = "dysk.h" |
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#+end_src |
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**** build.rs |
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#+begin_src rust :tangle build.rs |
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fn main() -> Result<(), cbindgen::Error> { |
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if let Ok(b) = cbindgen::generate(std::env::var("CARGO_MANIFEST_DIR").unwrap()) { |
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b.write_to_file("dysk.h"); Ok(())} |
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else { panic!("failed to generate dysk.h from cbindgen.toml") } } |
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#+end_src |
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** lib.rs |
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#+begin_src rust :tangle lib.rs |
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//! lib.rs --- dysk library |
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use std::ffi::{c_char, c_int, CString}; |
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#[no_mangle] |
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pub extern "C" fn hello() -> *const c_char { |
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CString::new("hello from rust").unwrap().into_raw()} |
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#[no_mangle] |
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pub extern "C" fn plus(a:c_int,b:c_int) -> c_int {a+b} |
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#[no_mangle] |
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pub extern "C" fn plus1(n:c_int) -> c_int {n+1} |
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#+end_src |
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** test.rs |
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#+begin_src rust :tangle test.rs |
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//! test.rs --- dysk test |
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fn main() { let mut i = 0u32; while i < 500000000 {i+=1; dysk::plus1(2 as core::ffi::c_int);}} |
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#+end_src |
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** compile |
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#+begin_src sh |
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cargo build --release |
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#+end_src |
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** load from SBCL |
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#+begin_src lisp :tangle dysk.lisp |
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;;; dysk.lisp |
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;; (dysk:hello) ;; => "hello from rust" |
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(defpackage :dysk |
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(:use :cl :sb-alien) |
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(:export :hello :plus :plus1)) |
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(in-package :dysk) |
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(load-shared-object #P"target/release/libdysk.so") |
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(define-alien-routine hello c-string) |
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(define-alien-routine plus int (a int) (b int)) |
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(define-alien-routine plus1 int (n int)) |
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#+end_src |
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** benchmark |
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#+begin_src shell |
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time target/release/dysk-test |
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#+end_src |
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#+begin_src lisp :tangle test.lisp |
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(time (dotimes (_ 500000000) (dysk:plus1 2))) |
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#+end_src |
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