wasm_thread

An std::thread replacement for wasm32 target.

This crate tries to closely replicate std::thread API, however, some features are not yet implemented or are even impossible to implement.

Running examples

Native

• Just cargo run --example simple

wasm32

• Build with ./build_wasm.sh or copy paste commands from the script if your environment does not support shell scripts. This custom build step is required because prebuilt standard library does not have support for atomics yet. Read more about this here.
• Serve examples directory over HTTP and open simple.html in browser. Inspect console output. You can use cargo install basic-http-server and basic-http-server examples.

Using as a library

• Add wasm_thread to your Cargo.toml.
• Replace use std::thread with use wasm_thread as thread. Note that some API might be missing.
• Adapt build_wasm.sh to your project. Currently only --no-modules target is supported.

Notes on wasm limitations

• Any blocking API (thread.join(), futures::block_on(), etc) on the main thread will freeze the browser for as long as lock is maintained. This also freezes any proxied functions, which means that worker spawning, network fetches and other similar asynchronous APIs will block also and can cause a deadlock. To avoid this, either run your main() in a worker thread or use async futures.
• Atomic locks (i32.atomic.wait to be specific) will panic on the main thread. This means that mutex.lock() will likely crash. Solution is the same as above.
• Only no-modules target is supported by wasm_bindgen. This will be lifted once browsers support modules in web workers.
• Web workers are normally spawned by providing a script URL, however, to avoid bundling scripts this library uses URL encoded blob web_worker.js to avoid HTTP fetch. wasm_bindgen generated .js shim script is still needed and a hack is used to obtain its URL. If this for some reason does not work in your setup, please report an issue or use Builder::wasm_bindgen_shim_url() to specify explicit URL.
• For additional information on wasm threading look at this blogpost or raytrace-parallel example.

Example output

Native: hi number 1 from the spawned thread ThreadId(2)! hi number 1 from the main thread ThreadId(1)! hi number 1 from the spawned thread ThreadId(3)! hi number 2 from the main thread ThreadId(1)! hi number 2 from the spawned thread ThreadId(2)! hi number 2 from the spawned thread ThreadId(3)!

Wasm: hi number 1 from the main thread ThreadId(1)! hi number 2 from the main thread ThreadId(1)! hi number 1 from the spawned thread ThreadId(2)! hi number 1 from the spawned thread ThreadId(3)! hi number 2 from the spawned thread ThreadId(2)! hi number 2 from the spawned thread ThreadId(3)!

As you can see wasm threads are only spawned after main() returns, because browser event loop cannot continue while main thread is blocked.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.