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Ensure that JsValue isn't considered Send #955

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merged 1 commit into from Oct 11, 2018

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alexcrichton
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The JsValue type wraps a slab/heap of js objects which is managed by
the wasm-bindgen shim, and everything here is not actually able to cross
any thread boundaries. When wasm actually has threads, for example, each
thread will have to have its own slab of objects generated by
wasm-bindgen, and indices in one slab aren't valid in any other slabs.

This is technically a breaking change because JsValue was previously
Send and Sync, but I'm hoping that in practice this isn't actually a
breaking change because nothing in wasm can be using threads which in
theory shouldn't activate the Send and/or Sync bounds.

The `JsValue` type wraps a slab/heap of js objects which is managed by
the wasm-bindgen shim, and everything here is not actually able to cross
any thread boundaries. When wasm actually has threads, for example, each
thread will have to have its own slab of objects generated by
wasm-bindgen, and indices in one slab aren't valid in any other slabs.

This is technically a breaking change because `JsValue` was previously
`Send` and `Sync`, but I'm hoping that in practice this isn't actually a
breaking change because nothing in wasm can be using threads which in
theory shouldn't activate the `Send` and/or `Sync` bounds.
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@fitzgen fitzgen left a comment

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yep

@alexcrichton alexcrichton merged commit e03e404 into rustwasm:master Oct 11, 2018
@alexcrichton alexcrichton deleted the non-send branch October 11, 2018 00:52
@upsuper
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upsuper commented Jan 22, 2019

Well, it is a breaking change since it breaks the use of lazy_static :)

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3 participants