[swift-users] UnsafeMutablePointer Swift 3 conversion
Patrice Kouame
pkouame at me.com
Sun Sep 4 00:28:57 CDT 2016
Cool. Another approach. Never thought of using assumingMemoryBound.
Need to read up on that. I wonder how both versions compare from a safety/security/performance stand point.
Behold the spinning cubes… ;-)
P
>
> On Sep 3, 2016, at 9:03 PM, Gerard Iglesias via swift-users <swift-users at swift.org> wrote:
>
> This is my funny version… I succeeded and I didn’t come back to find an other way…
>
> // 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().assumingMemoryBound(to: ShadowPass.self)
> shadowPtr.pointee = shadowPassData[0]
>
> //More Swift specific stuff - advance pointer and cast to MainPass
>
> //let mainPtr = UnsafeMutablePointer<MainPass>(shadowPtr.advanced(by: 1))
> let mainPtr = constantBufferForFrame.contents().advanced(by: MemoryLayout<ShadowPass>.size).assumingMemoryBound(to: MainPass.self)
> mainPtr.pointee = mainPassFrameData
>
> //Advance and cast to ObjectData
>
> //var ptr = UnsafeMutablePointer<ObjectData>(mainPtr.advanced(by: 1))
> var ptr = constantBufferForFrame.contents().advanced(by: MemoryLayout<ShadowPass>.size + MemoryLayout<MainPass>.size).assumingMemoryBound(to: ObjectData.self)
>
>
>> On 3 Sep 2016, at 19:22, Patrice Kouame <pkouame at me.com <mailto:pkouame at me.com>> wrote:
>>
>> 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 <mailto: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
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> swift-users mailing list
>>>>>>> swift-users at swift.org <mailto:swift-users at swift.org>
>>>>>>> https://lists.swift.org/mailman/listinfo/swift-users <https://lists.swift.org/mailman/listinfo/swift-users>
>>>>>>>
>>>>>>>
>>>>>>
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>>>>> _______________________________________________
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>>>>
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