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Add built-ins for creating/switching cooperative threads #557

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791006f
Add cooperative threads
lukewagner Aug 22, 2025
5fcd4c1
Add extra sentence about 'task.return' trapping in Concurrency.md
lukewagner Sep 2, 2025
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6 changes: 3 additions & 3 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ reference interpreter and test suite.

The Component Model is currently being incrementally developed and stabilized
as part of [WASI Preview 2]. The subsequent [WASI Preview 3] milestone will be
primarily concerned with the addition of [async support][Concurrency Model].
primarily concerned with the addition of [async and thread support][Concurrency
Model].

## Contributing

Expand All @@ -32,11 +33,10 @@ To contribute to any of these repositories, see the Community Group's
[IDL]: design/mvp/WIT.md
[Text Format]: design/mvp/Explainer.md
[Binary Format]: design/mvp/Binary.md
[Concurrency Model]: design/mvp/Async.md
[Concurrency Model]: design/mvp/Concurrency.md
[Canonical ABI]: design/mvp/CanonicalABI.md
[formal spec]: spec/
[W3C WebAssembly Community Group]: https://www.w3.org/community/webassembly/
[Contributing Guidelines]: https://webassembly.org/community/contributing/
[WASI Preview 2]: https://github.com/WebAssembly/WASI/tree/main/wasip2#readme
[WASI Preview 3]: https://github.com/WebAssembly/WASI/tree/main/wasip2#looking-forward-to-preview-3
[Async Support]: https://docs.google.com/presentation/d/1MNVOZ8hdofO3tI0szg_i-Yoy0N2QPU2C--LzVuoGSlE/edit?usp=share_link
24 changes: 17 additions & 7 deletions design/mvp/Binary.md
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Expand Up @@ -214,7 +214,7 @@ label' ::= len:<u32> l:<label> => l (if len = |l|)
valtype ::= i:<typeidx> => i
| pvt:<primvaltype> => pvt
resourcetype ::= 0x3f 0x7f f?:<funcidx>? => (resource (rep i32) (dtor f)?)
| 0x3e 0x7f f:<funcidx> cb?:<funcidx>? => (resource (rep i32) (dtor async f (callback cb)?)) 🚝
| 0x3e 0x7f f:<funcidx> cb?:<funcidx>? => (resource (rep i32) (dtor async f (callback cb)?)) 🧵
functype ::= 0x40 ps:<paramlist> rs:<resultlist> => (func ps rs)
paramlist ::= lt*:vec(<labelvaltype>) => (param lt)*
resultlist ::= 0x00 t:<valtype> => (result t)
Expand Down Expand Up @@ -288,14 +288,14 @@ canon ::= 0x00 0x00 f:<core:funcidx> opts:<opts> ft:<typeidx> => (canon lift
| 0x01 0x00 f:<funcidx> opts:<opts> => (canon lower f opts (core func))
| 0x02 rt:<typeidx> => (canon resource.new rt (core func))
| 0x03 rt:<typeidx> => (canon resource.drop rt (core func))
| 0x07 rt:<typeidx> => (canon resource.drop rt async (core func)) 🚝
| 0x07 rt:<typeidx> => (canon resource.drop rt async (core func)) 🧵
| 0x04 rt:<typeidx> => (canon resource.rep rt (core func))
| 0x08 => (canon backpressure.set (core func)) 🔀
| 0x09 rs:<resultlist> opts:<opts> => (canon task.return rs opts (core func)) 🔀
| 0x05 => (canon task.cancel (core func)) 🔀
| 0x0a 0x7f i:<u32> => (canon context.get i32 i (core func)) 🔀
| 0x0b 0x7f i:<u32> => (canon context.set i32 i (core func)) 🔀
| 0x0c cancel?:<cancel?> => (canon yield cancel? (core func)) 🔀
| 0x0c cancel?:<cancel?> => (canon thread.yield cancel? (core func)) 🔀
| 0x06 async?:<async?> => (canon subtask.cancel async? (core func)) 🔀
| 0x0d => (canon subtask.drop (core func)) 🔀
| 0x0e t:<typeidx> => (canon stream.new t (core func)) 🔀
Expand All @@ -320,13 +320,21 @@ canon ::= 0x00 0x00 f:<core:funcidx> opts:<opts> ft:<typeidx> => (canon lift
| 0x21 cancel?:<cancel?> m:<core:memidx> => (canon waitable-set.poll cancel? (memory m) (core func)) 🔀
| 0x22 => (canon waitable-set.drop (core func)) 🔀
| 0x23 => (canon waitable.join (core func)) 🔀
| 0x40 ft:<typeidx> => (canon thread.spawn_ref ft (core func)) 🧵
| 0x41 ft:<typeidx> tbl:<core:tableidx> => (canon thread.spawn_indirect ft tbl (core func)) 🧵
| 0x42 => (canon thread.available_parallelism (core func)) 🧵
| 0x26 => (canon thread.index (core func)) 🧵
| 0x27 ft:<typeidx> tbl:<core:tableidx> => (canon thread.new_indirect ft tbl (core func)) 🧵
| 0x28 cancel?:<cancel?> => (canon thread.switch-to cancel? (core func)) 🧵
| 0x29 cancel?:<cancel?> => (canon thread.suspend cancel? (core func)) 🧵
| 0x2a => (canon thread.resume-later (core func)) 🧵
| 0x2b cancel?:<cancel?> => (canon thread.yield-to cancel? (core func)) 🧵
| 0x40 shared?:<sh?> ft:<typeidx> => (canon thread.spawn_ref shared? ft (core func)) 🧵②
| 0x41 shared?:<sh?> ft:<typeidx> tbl:<core:tableidx> => (canon thread.spawn_indirect shared? ft tbl (core func)) 🧵②
| 0x42 shared?:<sh?> => (canon thread.available-parallelism shared? (core func)) 🧵②
async? ::= 0x00 =>
| 0x01 => async
cancel? ::= 0x00 =>
| 0x01 => cancellable 🚟
| 0x01 => cancellable 🧵
sh? ::= 0x00 =>
| 0x01 => shared 🧵②
opts ::= opt*:vec(<canonopt>) => opt*
canonopt ::= 0x00 => string-encoding=utf8
| 0x01 => string-encoding=utf16
Expand Down Expand Up @@ -510,6 +518,8 @@ named once.
repurposed.
* Most built-ins should have a `<canonopt>*` immediate instead of an ad hoc
subset of `canonopt`s.
* Add optional `shared` immediate to all canonical definitions (explicitly or
via `<canonopt>`) when shared-everything-threads (🧵②) is added.


[`core:byte`]: https://webassembly.github.io/spec/core/binary/values.html#binary-byte
Expand Down
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