OpenMP library linkage for Rust programs

This crate allows using OpenMP-dependent C code with Rust. It makes Cargo link to OpenMP, so that C static libraries linked with Rust programs can use OpenMP.

It can't be used with pure Rust programs (Rayon is a better choice for Rust).

NB: this crate can't automatically enable OpenMP for C code compiled from build scripts. You also need to pass -fopenmp//openmp flag to the C compiler (see usage below).

Requirements

Rust 1.42 or later
libgomp.* present in a directory printed by cc -print-search-dirs, or vcomp.dll on Windows
OpenMP-enabling flag set for any C code linked with the Rust program.

Usage

1. Adding Rust dependency

Add openmp-sys as a runtime dependency (e.g. cargo install cargo-edit; cargo add openmp-sys) and then add to your lib.rs:

extern crate openmp_sys;

2. Configuring C compiler

The C code being linked must be compiled with an OpenMP-enabling flag. For projects that use the cc crate it can be made easier. If you add openmp-sys also as a dev-depenency, it will set DEP_OPENMP_FLAG env var for your build.rs script with an appropriate flag such as -fopenmp or /openmp, depending on the target compiler. Pass this to cc build this way:

cc_build.flag(&std::env::var("DEP_OPENMP_FLAG").unwrap());

Static linking

Optionally, you can enable static feature or set OPENMP_STATIC=1 env var to link OpenMP statically, so that executables using it are usable on machines without a compiler installed. Only GCC supports this.

[dependencies.openmp]
features = ["static"]
version = "0.1"

macOS

In macOS Clang pretends to be the gcc executable, but doesn't support OpenMP. Install brew install gcc from Homebrew and compile with CC=gcc-9 cargo build. You may need to run cargo clean first if it doesn't take effect.

Static linking is recommended on macOS.