extension_host: Improve Wasmtime timeslicing behavior for extensions #24986
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Addresses the [discussion](zed-industries#24515) that goes into depth on why this is important when enabling async support with Wasmtime. The tldr; is, async mode puts component execution within a `Future::poll` call, which if the component code is malicious or just expensive, can then block a given async thread. With this change it should provide an upper bound on how long a given extension can run before yielding back and allowing another task to execute. This could be extended to also provide an upper bound to how long you would want a given call to take at all, as this implementation will still let it happily take forever, it just has to let other extensions have a turn. Happy to discuss more, and also make any changes in case I missed something here. Or close if this change isn't desired for any reason. Release Notes: - Improved wasmtime timeslicing behavior for extensions
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benbrandt
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| store.set_epoch_deadline(1); | ||
| store.epoch_deadline_async_yield_and_update(1); |
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Here there are a few other options:
- Change either the epoch interval or deadline to just put an upper bound on component execution (this is what Spin does)
- Do the callback version where you can decide if you want to yield or trap
No matter which way, since I believe you all have a timeout further up, the future will eventually get dropped, but any variation should still help.
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I will also say, as I did in the discussion, I'm happy to add some more test cases around this. I just wanted to put the code in a PR in case that made it easier to discuss first. |
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Closing this for now. We can continue discussion on the discussion as it probably needs to be ironed out which direction to push this before this would be mergeable anyway. |
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Addresses the discussion that goes into depth on why this is important when enabling async support with Wasmtime.
The tldr; is, async mode puts component execution within a
Future::pollcall, which if the component code is malicious or just expensive, can then block a given async thread.With this change it should provide an upper bound on how long a given extension can run before yielding back and allowing another task to execute.
This could be extended to also provide an upper bound to how long you would want a given call to take at all, as this implementation will still let it happily take forever, it just has to let other extensions have a turn.
Happy to discuss more, and also make any changes in case I missed something here. Or close if this change isn't desired for any reason.
Release Notes: