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Unhandled suspension in embedding API

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#95 11 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
15/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
wasm
Domain
api, compilers

Research direction

No files, tests, or entry points are named. Start by reviewing the questions about exnref, contref, meta-continuations, and embedding operations in this issue. Done requires an agreed representation and embedding API semantics for unhandled suspensions.

Written by the indexing model from the issue text.

Description

Some offline discussion turned up the issue of how to represent unhandled suspensions in the embedder API. Let's use this issue to discuss.

AFAICT an unhandled suspension is a pair of (something like) an exnref and a contref. An exnref is itself a pair of a tag and a payload, i.e. a vector of values. Tags in stack-switching add results, but I think they are only relevant for the static typing of handlers in the bytecode.

@rossberg had brought up the concept of a "meta-continuation". My understanding that that is basically a contref that could/should be resumable via the embedding API.

I think contref is pretty similar to a funcref from the embedder's perspective; invoking it is a meta-level operation which is dynamically-typed. The only differences I can see are:

  1. contref doesn't fit under the any heaptype hierarchy, so it should fail any dynamically-typed embedder operations that take an anyref,
  2. contref supports, or should support cont.bind, if we have that embedder operation,
  3. invoking a contref could suspend (but I think invoking a funcref can also suspend), and
  4. it may be represented differently, since it could be a continuation object or a pair of a version+stack resource.
Dominant language
WebAssembly
Stars
216
Forks
19
No merged PRs in 30d

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