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[Overview] Change wake to use unsigned semantics #110

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Nov 15, 2018
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[Overview] Change wake to use unsigned semantics #110

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[Overview] Change wake to use unsigned semantics
binji Nov 14, 2018
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Remove table
binji Nov 15, 2018
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unsigned return value
binji Nov 15, 2018
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22 changes: 9 additions & 13 deletions proposals/threads/Overview.md
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Expand Up @@ -381,9 +381,12 @@ when the agent is suspended, it will not be [spuriously woken](https://en.wikipe
The agent is only woken by `atomic.wake` (or [`Atomics.wake`][] in the web
embedding).

When an agent is suspended, if the number of waiters (including this one) is
equal to 2<sup>32</sup>, then trap.

* `i32.atomic.wait`: load i32 value, compare to expected (as `i32`), and wait for wake at same address
* `i64.atomic.wait`: load i64 value, compare to expected (as `i64`), and wait for wake at same address

For the web embedding, `i32.atomic.wait` is equivalent in behavior to executing the following:

1. Let `memory` be a `WebAssembly.Memory` object for this module.
Expand All @@ -394,7 +397,7 @@ For the web embedding, `i32.atomic.wait` is equivalent in behavior to executing
as described above.
1. Return an `i32` value as described in the above table:
("ok" -> `0`, "not-equal" -> `1`, "timed-out" -> `2`).

`i64.atomic.wait` has no equivalent in ECMAScript as it is currently specified, as there is
no `Int64Array` type, and an ECMAScript `Number` cannot represent all values of a
64-bit integer. That said, the behavior can be approximated as follows:
Expand All @@ -418,26 +421,19 @@ no `Int64Array` type, and an ECMAScript `Number` cannot represent all values of
### Wake

The wake operator takes two operands: an address operand and a wake count as an
`i32`. The operation will wake as many waiters as are waiting on the same
effective address, up to the maximum as specified by `wake count`. The operator
returns the number of waiters that were woken as an `i32`.

`wake count` value | Behavior |
| ---- | ---- |
| `wake count` < 0 | Wake all waiters |
| `wake count` == 0 | Wake no waiters |
| `wake count` > 0 | Wake min(`wake count`, `num waiters`) waiters |
unsigned `i32`. The operation will wake as many waiters as are waiting on the
same effective address, up to the maximum as specified by `wake count`. The
operator returns the number of waiters that were woken as an unsigned `i32`.

* `atomic.wake`: wake up `wake count` threads waiting on the given address via `i32.atomic.wait` or `i64.atomic.wait`

For the web embedding, `atomic.wake` is equivalent in behavior to executing the following:

1. Let `memory` be a `WebAssembly.Memory` object for this module.
1. Let `buffer` be `memory`([`Get`][](`memory`, `"buffer"`)).
1. Let `int32array` be [`Int32Array`][](`buffer`).
1. Let `fcount` be `count` if `count` is >= 0, otherwise `∞`.
1. Let `result` be [`Atomics.wake`][](`int32array`, `address`, `fcount`).
1. Trap if `result` is >= 2**32.
1. Return `result` converted to an `i32`.

## [JavaScript API][] changes
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