Add support for compiling with atomics for Node.js
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daxpedda
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newpavlov
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As discussed in #541. This PR adds the following improvements: - Caching of the global `Crypto` object. - Detecting if our Wasm memory is based on a `SharedArrayBuffer`. If not, we can copy bytes directly into our memory instead of having to go through JS. This saves allocating the buffer in JS and copying the bytes into Wasm memory. This is also the most common path. `SharedArrayBuffer` requires `target_feature = "atomics"`, which is unstable and requires Rust nightly. See #559 (comment) for full context. - The atomic path only creates a sub-array when necessary, potentially saving another FFI call. - The atomic path will now allocate an `Uint8Array` with the minimum amount of bytes necessary instead of a fixed size. - The maximum chunk size for the non-atomic path and the maximum `Uint8Array` size for the atomic paths have been increased to 65536 bytes: the maximum allowed buffer size for `Crypto.getRandomValues()`. All in all this should give a performance improvement of ~5% to ~500% depending on the amount of requested bytes and which path is taken. See #559 (comment) for some benchmark results. This spawned a bunch of improvements and fixes in `wasm-bindgen` that are being used here: - rustwasm/wasm-bindgen#4315 - rustwasm/wasm-bindgen#4316 - rustwasm/wasm-bindgen#4318 - rustwasm/wasm-bindgen#4319 - rustwasm/wasm-bindgen#4340
daxpedda
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atomics for Node.js
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Our Node.js shim doesn't provide a way to pass in a
WebAssembly.MemoryorSharedArrayBuffer, so we just set the memory to not be imported but simply instantiated in Wasm.I don't know the historical context behind LLVM emitting the memory as an import by default when using atomics.
EDIT: LLVM does not, Rust does.