Make AsyncStream Sync even if the inner future is not #115
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The AsyncStream has a few methods that that take &self so we don't necessarily want to unconditionally impl Send for it. However, we only access the inner future by calling Future::poll. We can then make AsyncStream Send in a way that is more obviously safe by wrapping the inner stream in SyncWrapper from [0]. This gets the same effect (AsyncStream<T> is Sync) but uses only unsafe blocks that are more obviously safe. [0]: https://internals.rust-lang.org/t/what-shall-sync-mean-across-an-await/12020/2
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I think the test failures are due to changes in rust 1.85 and not this PR (looks like |
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There's an old issue (#28) that asked for this and was closed because a
&selfmethod was added toAsyncStreamin #40. The issue has a pretty good description of why I would like this.However, if we copy the
SyncWrappertype from the internals thread mentioned in that issue then we can use it to wrap the future withinAsyncStreamand get the whole thing to implementSync.The tradeoff is that it is no longer possible to print the debug representation of the inner generator as that would require a shared reference to the future. I don't believe it is currently possible to create an
AsyncStreamthat actually implementsDebugusing the public API of the crate (as async blocks do not implementDebug) but I figure this is a trade-off worth bringing up. As a middle-ground it might be possible to use some hacks to only format the inner type when it implementsSync.