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Normative: Update RevalidateAtomicAccess to account for all bytes of a TypedArray element #3926

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Normative: Update RevalidateAtomicAccess to account for all bytes of a TypedArray element #3926

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6 changes: 4 additions & 2 deletions spec.html
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Original file line number Diff line number Diff line change
Expand Up @@ -47213,7 +47213,9 @@ <h1>
1. NOTE: Bounds checking is not a synchronizing operation when _ta_'s backing buffer is a growable SharedArrayBuffer.
1. Let _taRecord_ be ? ValidateTypedArrayBounds(_ta_, ~unordered~).
1. Assert: _byteIndexInBuffer_ ≥ _ta_.[[ByteOffset]].
1. If _byteIndexInBuffer_ ≥ _taRecord_.[[CachedBufferByteLength]], throw a *RangeError* exception.
1. Let _elementSize_ be TypedArrayElementSize(_ta_).
1. Let _elementLastByteIndex_ be _byteIndexInBuffer_ + _elementSize_ - 1.
1. If _elementLastByteIndex_ ≥ _taRecord_.[[CachedBufferByteLength]], throw a *RangeError* exception.
1. Return ~unused~.
</emu-alg>
</emu-clause>
Expand Down Expand Up @@ -47720,8 +47722,8 @@ <h1>Atomics.notify ( _ta_, _index_, _count_ )</h1>
1. Let _intCount_ be ? ToIntegerOrInfinity(_count_).
1. Set _count_ to max(_intCount_, 0).
1. Let _buffer_ be _ta_.[[ViewedArrayBuffer]].
1. Let _block_ be _buffer_.[[ArrayBufferData]].
1. If IsSharedArrayBuffer(_buffer_) is *false*, return *+0*<sub>𝔽</sub>.
1. Let _block_ be _buffer_.[[ArrayBufferData]].

@gibson042 gibson042 Jul 24, 2026 •
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Atomics.notify notably does not use RevalidateAtomicAccess, so shrinking a length-tracking TypedArray in e.g. index.valueOf and then returning an index made out-of-bounds by the resize does not throw an exception (Atomics.notify(ta, { valueOf() { assert(ta.length > 0); ta.buffer.resize(0); assert(ta.length === 0); return 0; } }) === 0, except that V8 does seem to revalidate). But the primary use for Atomics.notify is with TypedArrays backed by shared ArrayBuffers, which cannot shrink and thus cannot encounter such a scenario. This PR preserves the behavior; I just thought it'd be worth highlighting.

1. Let _waiterList_ be GetWaiterList(_block_, _byteIndexInBuffer_).
1. Perform EnterCriticalSection(_waiterList_).
1. Let _waiters_ be RemoveWaiters(_waiterList_, _count_).
Expand Down
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