There are a number of async task executors available in Rust's ecosystem. However, most (if not all?) of them rely on primitives that might not be available or optimal for WebAssembly deployment at the time.
Include this dependency in your Cargo.toml:
toml
[dependencies]
wasm-rs-async-executor = "0.6.1"
wasm-rs-async-executor is expected to work on stable Rust, 1.49.0 and higher up. It may also
work on earlier versions. This hasn't been tested yet.
Currently, it's been only tested on wasm32-unknown-unknown, but excluding cooperative functionality,
it may work on other wasm32 and non-wasm32 targets. Further testing is to be completed.
Please note that this library hasn't received much analysis in terms of safety
and soundness. Some of the caveats related to that might never be resolved
completely. This is an ongoing development and the maintainer is aware of
potential pitfalls. Any productive reports of unsafeties or unsoundness are
welcomed (whether they can be resolved or simply walled with unsafe for end-user
to note).
Q: Why not just use wasm-bindgen-futures?
A: (short) In many cases, wasm-bindgen-futures is just fine
A: (longer) There are some subtle differences in the way wasm-rs-async-executor exposes its functionality. The
core idea behind it is to expose a reasonable amount of explicit controls over the its operations. You need
to run the executor explicitly, you can block on certain futures (again, explicitly -- which gives you a limited
ability to do scoped futures). It does come with minor trade-offs. For example, if you want to use async APIs from
your host environment, you can't simply await on then, as the executor won't yield to the browser until told to do
so (using yield_async(future).await). Ultimately, if this amount of control is beneficial for your case, then perhaps
this executor is waranted. It is also important to note that currently wasm-rs-async-executor does not support
WebAssembly multi-threading in any way. wasm-bindgen-futures does, if the standard library is built with support for it.
It is planned to support this, but hasn't been high priority so far due to
current state of things in Rust.
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