Caveat about async in create-subscription README (#12469)
* Caveat about async in create-subscription README * Address Sophie's comments * Dan's nits
Andrew Clark committed
Mar 27, 2018 at 16:50 UTC
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packages/create-subscription/README.md
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@@ -11,6 +11,16 @@ Other cases have **better long-term solutions**:
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* I/O subscriptions (e.g. notifications) that update infrequently should use [`simple-cache-provider`](https://github.com/facebook/react/blob/master/packages/simple-cache-provider/README.md) instead.
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* Complex libraries like Relay/Apollo should manage subscriptions manually with the same techniques which this library uses under the hood (as referenced [here](https://gist.github.com/bvaughn/d569177d70b50b58bff69c3c4a5353f3)) in a way that is most optimized for their library usage.
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+## Limitations in async mode
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+The main motivation for `create-subscription` is to provide a way for library authors to ensure compatibility with React's upcoming asynchronous rendering mode. `create-subscription` guarantees correctness in async mode, accounting for the subtle bugs and edge cases that a library author might otherwise miss.
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+However, it achieves correctness by sometimes de-opting to synchronous mode, obviating the benefits of async rendering. This is an inherent limitation of storing state outside of React's managed state queue and rendering in response to a change event.
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+The effect of de-opting to sync mode is that the main thread may periodically be blocked (in the case of CPU-bound work), and placeholders may appear earlier than desired (in the case of IO-bound work).
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+For **full compatibility** with asynchronous rendering, including both **time-slicing** and **React Suspense**, the suggested longer term solution is to move to one of the patterns described in the previous section.
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## What types of subscriptions can this support?
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This abstraction can handle a variety of subscription types, including: