rayon_wasm : "Operation not supported on this platform" when setting number of global threads to be used

[mtb0x1]

(rayon_wasm v1.6.2).

Running the code below in browser after compiling it to wasm, results in an error.

use rayon_wasm::ThreadPoolBuilder;


let cpus_in_use =5;
ThreadPoolBuilder::new()
.num_threads(cpus_in_use)
.build_global()
.unwrap();

Error :

value: ThreadPoolBuildError { kind: IOError(Error { kind: Unsupported, message: "operation not supported on this platform"})}

is this an expected behavior ? if yes what are the alternatives if there are any ?

Thanks.

[cuviper]

rayon-wasm is an unofficial forked publication, as noted here: #1019 (comment). Please use rayon 1.7.0.

That wasm support is just a fallback that lets rayon work single-threaded, but that's only applied when you leave num_threads unspecified. The target does not support threads, so std::thread::spawn is returning Unsupported.

With Rust nightly, you can build a version of the target with atomics, and threading may work. See the documentation here: https://github.com/GoogleChromeLabs/wasm-bindgen-rayon

There are also proposals in motion to add real supported WASI threading: rust-lang/compiler-team#574, rust-lang/compiler-team#607, rust-lang/compiler-team#661.