jextract/ffm: Support [UInt8] parameters#477
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ktoso
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Dec 3, 2025
ktoso
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Dec 3, 2025
| """ | ||
| @_cdecl("swiftjava_SwiftModule_acceptArray_array") | ||
| public func swiftjava_SwiftModule_acceptArray_array(_ array_pointer: UnsafeRawPointer, _ array_count: Int) { | ||
| acceptArray(array: [UInt8](UnsafeRawBufferPointer(start: array_pointer, count: array_count))) |
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Today we end up with 2 copies because of this.
Instead, we should accept a raw pointer that we know is an swift array of the rtight type here.
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For some performance follow up work: #478 because for now passing arrays will not be ideasl |
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Dec 3, 2025
| let cdeclParameters = [ | ||
| SwiftParameter( | ||
| convention: .byValue, | ||
| parameterName: "\(parameterName)_pointer", |
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We have naming inconsistency; these should be $ and not _ but seems we got this inconsistency already from the Data work -- lets fix it separately, since this made the PR kinda big
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| printParameterDescriptorClasses(&printer, cFunc) | ||
| if let outCallback = translated.translatedSignature.result.outCallback { | ||
| printUpcallParameterDescriptorClasses(&printer, outCallback) | ||
| } else { // FIXME: not an "else" |
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should probably just fix this right away
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will do later, after all
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These cause severe copying as we must copy the Java array into an off heap memory segment and then we must copy AGAIN into the Swift Array (!), so this is deeply inefficient and you should always prefer pointers of
Datawhich we had support for already earlier.Edit: Returning an array is now efficient, we're able to return [UInt8] which gets directly copied from native memory into an
byte[]on the heap 🥳 In a single copy.We can do better with other types, but this is the best we can hope to achieve for native arrays on Swift an Java side.
We'll do even better with other types by keeping the native memory retained etc. This is the most convenient though.
However, this is useful for convenience and we should offer this anyway.