[swift-users] UnsafeMutablePointer Swift 3 conversion
Patrice Kouame
pkouame at me.com
Sat Sep 3 12:22:42 CDT 2016
Gerard-
Excellent! Looking forward to seeing your fix (hoping you get your book back soon ;-) )
I think Xcode/Swift gags on the last ptr advance to objectData. I recently tried another variant using withUnsafeMutablePointer like this:
var ptr : UnsafeMutablePointer<ObjectData> = withUnsafeMutablePointer(to: &mainPtr) {
$0.withMemoryRebound(to: ObjectData.self, capacity: objectsToRender) {
$0.pointee = renderables[0].objectData
}
}
..but still crashes with no hints.
My bug report also mentions that the Xcode migration/conversion tool is incomplete.
It handles the “simpler" UnsafeMutableRawPointer<X> to UnsafeMutablePonter<Y> with bindMemory cases correctly (one still has to mind the capacity value though)
In all fairness, migrating/converting automagically in these cases is always a little bit tricky - the proposed Xcode fixes should always be reviewed by a human...
Patrice
> On Sep 3, 2016, at 1:05 PM, Gerard Iglesias via swift-users <swift-users at swift.org> wrote:
>
> Ok
>
> For the record I succeeded this transformation phase last week
>
> I remember the tedious stuff to advance pointer from one struct to the other kind of struct... it worked
>
> But I don't have my MacBook with me, only the phone, the six :)
>
> Gérard
>
> Le 3 sept. 2016 à 18:22, Patrice Kouame <pkouame at me.com <mailto:pkouame at me.com>> a écrit :
>
>> Indeed. There is a difference between stride and size, but I interpreted capacity incorrectly for my purposes. It should indicate the number of <T> elements (not their size - right?) and the snippets below should work.
>>
>> Still, compiler crashes and Xcode IDE is left in inconsistent state. So I filed this Apple radar against Developer Tools.
>>
>> 28150447 - Swift 3 UnsafeMutablePointer conversion crashes the compiler and IDE
>> Should I file a Swift bug too? Would that be helpful?
>>
>> Regards, Patrice
>>
>>> On Sep 3, 2016, at 11:39 AM, Gerard Iglesias via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>>>
>>> Hello,
>>>
>>> I think that it is more secure to use stride in place of size, sometimes it is not the same value.
>>>
>>> I use it in my own use of raw bindings
>>>
>>> Regards
>>>
>>> Gérard
>>>
>>> Le 3 sept. 2016 à 10:03, Patrice Kouame via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> a écrit :
>>>
>>>> Hi Jacob -
>>>>
>>>> I think you’re right. “capacity” should be the count of type T elements in my buffer. So in my case that line should read
>>>>
>>>> let shadowPtr = constantBufferForFrame.contents().bindMemory(to: ShadowPass.self, capacity: shadowPassData.count)
>>>>
>>>> The withMemoryRebound calls need similar adjustments. The pointer to MainPass is actually a single structure to it should be safe to do this
>>>>
>>>> let mainPtr : UnsafeMutablePointer<MainPass> = shadowPtr.advanced(by: 1).withMemoryRebound(to: MainPass.self, capacity: 1) {
>>>> $0.pointee = mainPassFrameData
>>>> }
>>>>
>>>> Whereas the unsafe pointer to <ObjectData> is actually a buffer of renderable objects, so this should work:
>>>>
>>>> var ptr : UnsafeMutablePointer<ObjectData> = mainPtr.advanced(by: 1).withMemoryRebound(to: ObjectData.self, capacity: objectsToRender) {_ in
>>>> }
>>>>
>>>> There are surely ways to refactor and simplify this, but I’m trying to retain as much of the original sample code approach as possible.
>>>>
>>>> However, the compiler still segs badly.
>>>> Xcode also borks an internal error often. Only cleaning or restarting the project can clear up that state.
>>>> Compilers (or Playgrounds for that matter) should never crash, and I’m not sure where to file this bug : Swift or Apple radar against Xcode or both? I now Xcode 8 is beta but…it’s been doing this for quite a while now...
>>>>
>>>> In both our “close to the metal” (no pun intended) cases, it seems like a lot of churning for very little gain. Don’t you think? The easier, but “unsafe” casting afforded previously did the trick with the normal caveats.
>>>> Don’t get me wrong, I love Swift and “get" all the neat type safety features. Guess we can’t have our cake and eat it too, especially when interfacing with “unsafe” C APIs.
>>>>
>>>> Anyway, back to rtfm … maybe some of the Swift Gods can chime in? ;-)
>>>>
>>>> I must be doing something stupid...Patrice
>>>>
>>>>> On Sep 3, 2016, at 2:32 AM, Jacob Bandes-Storch <jtbandes at gmail.com <mailto:jtbandes at gmail.com>> wrote:
>>>>>
>>>>> Hi Patrice,
>>>>> I don't have a solution for you, but I just wanted to point out what I think may be an error with your use of the new UnsafeRawPointer APIs:
>>>>>
>>>>> constantBufferForFrame.contents().bindMemory(to: ShadowPass.self, capacity: MemoryLayout<ShadowPass>.size)
>>>>>
>>>>> I believe the `capacity` should actually be the number of ShadowPass elements in the buffer, not the size of each element. Using `bindMemory(to: ShadowPass.self` already implies that MemoryLayout<ShadowPass>.size is the size of each element.
>>>>>
>>>>> More info at https://developer.apple.com/reference/swift/unsaferawpointer/2428875-bindmemory <https://developer.apple.com/reference/swift/unsaferawpointer/2428875-bindmemory>
>>>>>
>>>>> I just updated a small Metal project of mine to Swift 3. I ran into some compiler (playground) crashes, but it does seem to work most of the time. Although I only have 1 buffer :-) https://github.com/jtbandes/Metalbrot.playground <https://github.com/jtbandes/Metalbrot.playground>
>>>>>
>>>>> Jacob
>>>>>
>>>>> On Fri, Sep 2, 2016 at 11:00 AM, Patrice Kouame via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>>>>> Hi all -
>>>>>
>>>>> I’m converting Apple’s Swift Sample "Adopting Metal II: Designing and Implementing a Real-World Metal Renderer” in Xcode 8 beta6 to the latest UnsafeMutablePointer API for untyped memory access.
>>>>> Changes are necessary in MetalView.swift (Apple hasn’t updated their sample code for the latest beta yet…)
>>>>> The Swift Compiler crashes (Segmentation Fault: 11) on the attempt:
>>>>>
>>>>> // Grab a pointer to the constant buffer's data store
>>>>> // Since we are using Swift, it is easier to cast the pointer to the ShadowPass type to fill the constant buffer
>>>>> // We need to make a copy of these so the block captures the correct data
>>>>>
>>>>> // let shadowPtr = UnsafeMutablePointer<ShadowPass>(constantBufferForFrame.contents())
>>>>> let shadowPtr = constantBufferForFrame.contents().bindMemory(to: ShadowPass.self, capacity: MemoryLayout<ShadowPass>.size)
>>>>> shadowPtr.pointee = shadowPassData[0]
>>>>>
>>>>> //More Swift specific stuff - advance pointer and cast to MainPass
>>>>>
>>>>> // let mainPtr = UnsafeMutablePointer<MainPass>(shadowPtr.advanced(by: 1))
>>>>> // mainPtr.pointee = mainPassFrameData
>>>>> let mainPtr : UnsafeMutablePointer<MainPass> = shadowPtr.advanced(by: 1).withMemoryRebound(to: MainPass.self, capacity: MemoryLayout<MainPass>.size) {
>>>>> $0.pointee = mainPassFrameData
>>>>> }
>>>>>
>>>>> //Advance and cast to ObjectData
>>>>>
>>>>> // var ptr = UnsafeMutablePointer<ObjectData>(mainPtr.advanced(by: 1))
>>>>> var ptr : UnsafeMutablePointer<ObjectData> = mainPtr.advanced(by: 1).withMemoryRebound(to: ObjectData.self, capacity: MemoryLayout<ObjectData>.size) {_ in
>>>>> }
>>>>>
>>>>> let shadowOffset = 0
>>>>> let mainPassOffset = MemoryLayout<ShadowPass>.size + shadowOffset
>>>>> let objectDataOffset = MemoryLayout<MainPass>.size + mainPassOffset
>>>>>
>>>>> // Update position of all the objects
>>>>> if multithreadedUpdate {
>>>>> DispatchQueue.concurrentPerform(iterations: objectsToRender) { i in
>>>>> let thisPtr = ptr.advanced(by: i)
>>>>> _ = self.renderables[i].UpdateData(ptr, deltaTime: 1.0/60.0)
>>>>> }
>>>>> }
>>>>> else {
>>>>> for index in 0..<objectsToRender {
>>>>> ptr = renderables[index].UpdateData(ptr, deltaTime: 1.0/60.0)
>>>>> }
>>>>> }
>>>>>
>>>>> ptr = ptr.advanced(by: objectsToRender)
>>>>>
>>>>> _ = groundPlane!.UpdateData(ptr, deltaTime: 1.0/60.0)
>>>>>
>>>>> Any help is appreciated. I have the latest Xcode log handy if necessary. Here’s a clip of the stack trace.
>>>>>
>>>>> 0 swift 0x000000010714a99d PrintStackTraceSignalHandler(void*) + 45
>>>>> 1 swift 0x000000010714a3e6 SignalHandler(int) + 470
>>>>> 2 libsystem_platform.dylib 0x00007fff91461bba _sigtramp + 26
>>>>> 3 libsystem_platform.dylib 000000000000000000 _sigtramp + 1857676384
>>>>> 4 swift 0x00000001047207b3 (anonymous namespace)::SILGenApply::visitExpr(swift::Expr*) + 51
>>>>> 5 swift 0x0000000104723ace (anonymous namespace)::SILGenApply::visitApplyExpr(swift::ApplyExpr*) + 5182
>>>>> 6 swift 0x0000000104711cc1 prepareApplyExpr(swift::Lowering::SILGenFunction&, swift::Expr*) + 273
>>>>> 7 swift 0x00000001047624e7 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 103
>>>>> 8 swift 0x0000000104762313 swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*) + 195
>>>>> 9 swift 0x000000010474fbc3 swift::Lowering::SILGenFunction::emitPatternBinding(swift::PatternBindingDecl*, unsigned int) + 195
>>>>> 10 swift 0x00000001047077bd swift::ASTVisitor<swift::Lowering::SILGenFunction, void, void, void, void, void, void>::visit(swift::Decl*) + 125
>>>>> 11 swift 0x00000001047c0019 swift::ASTVisitor<(anonymous namespace)::StmtEmitter, void, void, void, void, void, void>::visit(swift::Stmt*) + 4169
>>>>> 12 swift 0x00000001047809ba swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 314
>>>>> 13 swift 0x00000001046fd775 swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*)::$_1::operator()(swift::SILFunction*) const + 1877
>>>>> 14 swift 0x00000001046fc322 swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 626
>>>>> 15 swift 0x00000001047c7007 (anonymous namespace)::SILGenType::emitType() + 1271
>>>>> 16 swift 0x00000001047c6a9e swift::Lowering::SILGenModule::visitNominalTypeDecl(swift::NominalTypeDecl*) + 30
>>>>> 17 swift 0x0000000104709093 swift::Lowering::SILGenModule::emitSourceFile(swift::SourceFile*, unsigned int) + 1795
>>>>> 18 swift 0x000000010470ad4d swift::SILModule::constructSIL(swift::ModuleDecl*, swift::SILOptions&, swift::FileUnit*, llvm::Optional<unsigned int>, bool, bool) + 1629
>>>>> 19 swift 0x00000001045621bf performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*) + 19487
>>>>> 20 swift 0x000000010455b2c5 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 17029
>>>>> 21 swift 0x000000010451888d main + 8685
>>>>> 22 libdyld.dylib 0x00007fff91255255 start + 1
>>>>>
>>>>>
>>>>> Patrice
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>
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