Stream: git-wasmtime

Topic: wasmtime / PR #11442 Make table growth a true `async fn`

Wasmtime GitHub notifications bot (Aug 15 2025 at 21:46):

alexcrichton opened PR #11442 from alexcrichton:really-start-the-async-journey to bytecodealliance:main:

Upon further refactoring and thinking about #11430 I've realized that we might be able to sidestep T: Send on the store entirely which would be quite the boon if it can be pulled off. The realization I had is that the main reason for this was &mut dyn VMStore on the stack, but that itself is actually a bug in Wasmtime (#11178) and shouldn't be done. The functions which have this on the stack should actually ONLY have the resource limiter, if configured. This means that while the ResourceLimiter{,Async} traits need a Send supertrait that's relatively easy to add without much impact. My hunch is that plumbing this through to the end will enable all the benefits of #11430 without requiring adding T: Send to the store.

This commit starts out on this journey by making table growth a true async fn. A new internal type is added to represent a store's limiter which is plumbed to growth functions. This represents a hierarchy of borrows that look like:

• StoreInner<T>
  • StoreResourceLimiter<'_>
  • StoreOpaque
    • Pin<&mut Instance>
      • &mut vm::Table

This notably, safely, allows operating on vm::Table with a StoreResourceLimiter at the same time. This is exactly what's needed and prevents needing to have &mut dyn VMStore, the previous argument, on the stack.

This refactoring cleans up unsafe blocks in table growth right now which manually uses raw pointers to work around the borrow checker. No more now!

I'll note as well that this is just an incremental step. What I plan on doing next is handling other locations like memory growth, memory allocation, and table allocation. Each of those will require further refactorings to ensure that things like GC are correctly accounted for so they're going to be split into separate PRs. Functionally though this PR should have no impact other than a fiber is no longer required for Table::grow_async.

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Wasmtime GitHub notifications bot (Aug 15 2025 at 21:46):

alexcrichton requested pchickey for a review on PR #11442.

Wasmtime GitHub notifications bot (Aug 15 2025 at 21:46):

alexcrichton requested wasmtime-core-reviewers for a review on PR #11442.

Wasmtime GitHub notifications bot (Aug 15 2025 at 22:03):

alexcrichton updated PR #11442.

Wasmtime GitHub notifications bot (Aug 18 2025 at 18:01):

pchickey submitted PR review.

Wasmtime GitHub notifications bot (Aug 18 2025 at 18:23):

alexcrichton merged PR #11442.

Last updated: Dec 06 2025 at 07:03 UTC