Fix BufferSource algorithms for shared and resizable buffers
#1529
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@annevk Could you assign reviewer(s) to this? Thanks! 🙏 |
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Co-authored-by: Anne van Kesteren <[email protected]>
Co-authored-by: Anne van Kesteren <[email protected]>
MattiasBuelens
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Nov 24, 2025
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Quick self-review.
| 1. [=/Assert=]: |jsBufferSource| is a [=typed array type=] instance. | ||
| 1. Let |taRecord| be [$MakeTypedArrayWithBufferWitnessRecord$](|jsBufferSource|, | ||
| Seq-Cst). | ||
| 1. Return [$TypedArrayByteLength$](|taRecord|). |
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TypedArrayByteLength asserts that IsTypedArrayOutOfBounds(taRecord) is false, which we didn't explicitly check. We should check for that, to align with %TypedArray%.prototype.byteLength.
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| 1. Return [$TypedArrayByteLength$](|taRecord|). | |
| 1. If [$IsTypedArrayOutOfBounds$](|taRecord|) is true, return 0. | |
| 1. Return [$TypedArrayByteLength$](|taRecord|). |
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| 1. Otherwise, if [$IsSharedArrayBuffer$](|jsBufferSource|) is true: | ||
| 1. [=/Assert=]: |jsBufferSource| is a {{SharedArrayBuffer}}. | ||
| 1. Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst). | ||
| 1. Otherwise: | ||
| 1. [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}}. | ||
| 1. Return |jsBufferSource|.\[[ArrayBufferByteLength]]. |
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ArrayBufferByteLength supports both ArrayBuffer and SharedArrayBuffer, so we can combine these steps.
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| 1. Otherwise, if [$IsSharedArrayBuffer$](|jsBufferSource|) is true: | |
| 1. [=/Assert=]: |jsBufferSource| is a {{SharedArrayBuffer}}. | |
| 1. Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst). | |
| 1. Otherwise: | |
| 1. [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}}. | |
| 1. Return |jsBufferSource|.\[[ArrayBufferByteLength]]. | |
| 1. Otherwise: | |
| 1. [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}} or a {{SharedArrayBuffer}}. | |
| 1. Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst). |
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Previously, many
BufferSourcealgorithms were using internal slots such as[[ByteOffset]]and[[ByteLength]]directly. However, with the addition ofSharedArrayBuffer(#353, #1311) and[AllowResizable](#982), this comes with extra caveats:SharedArrayBuffer, we need to useArrayBufferByteLengthto matchSharedArrayBuffer.prototype.byteLength.TypedArrayByteLength. Similarly, for a length-trackingDataView, we need to useGetViewByteLength.DataView, we first need to check if the view is still inbounds usingIsArrayBufferViewOutOfBounds.Transferring an
ArrayBuffermust also take into account whether it should remain resizable or not. Fortunately, we can use the newArrayBufferCopyAndDetachoperation for that.preserveResizabilityparameter to "transfer anArrayBuffer", so specifications can choose whether to preserve resizability or not. By default, this is not preserved. (Most specs aren't using[AllowResizable]yet anyway.)realmparameter of that algorithm, sinceArrayBufferCopyAndDetachdoesn't accept such a parameter. According to WebDex, no specs were actually using that parameter anyway.Open questions:
SharedArrayBuffer, what memory ordering should we use? ECMAScript seems to useSEQ-CSTpretty much everywhere (e.g.%TypedArray%.prototype.byteLength), but "get a copy of the bytes" usesUNORDEREDforGetValueFromBuffer.Fixes #1312.
Fixes #1385.
(See WHATWG Working Mode: Changes for more details.)
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