Add a sync feature to common, core, and tensor

[AlexErrant]

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Failed with the same error as last time, more or less.

Related Issues/PRs

Resolves #865.

Continuing the discussion from the above issue: After a truly embarrassing amount of spinning in circles, I don't think I can get Asyncify to work with wgpu. WGPU is, at its foundation, async, and critical apis don't have a synchronous version. Asyncify only works on wasm files. WGPU is async Rust, so asyncify can't "de-async" it for our consumption.

Changes

So instead I pull the same trick as last time and feature flag stuff. I add a sync feature that I can use to get sync behavior when targeting WASM.

Testing

Add

burn = {path = "../../burn", default-features = false, features = ["train-minimal", "ndarray-no-std", "sync"]}
getrandom = { version = "0.2", features = ["js"] }

to https://github.com/burn-rs/burn/blob/main/examples/mnist-inference-web/Cargo.toml, delete this await, and observe that ./build-for-web.sh ndarray builds.

[AlexErrant]

Maybe this'll fix CI?

[nathanielsimard]

Maybe we should rename the feature flag to something like wasm-sync since it exclusively modifies the behavior when targeting wasm. Another option is to introduce a feature flag called async, but it could be misleading, as most of the execution relies on asynchronous operations using channels.

Just the name sync is also misleading, since even when not enabled, the APIs are sync when not targeting wasm.

[nathanielsimard]

I think I would use burn-core to pass the sync feature flag to those crates instead of adding them to burn.

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[AlexErrant]

Oh hah I did not expect that to fix CI.

[nathanielsimard]

@AlexErrant It was a setting problem, so just a trigger would fix it!