[swift-users] UnsafeMutablePointer Swift 3 conversion

Gerard Iglesias gerard_iglesias at me.com
Sat Sep 3 12:05:25 CDT 2016


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> 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> 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> 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> 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
>>>> 
>>>> 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
>>>> 
>>>> Jacob
>>>> 
>>>>> On Fri, Sep 2, 2016 at 11:00 AM, Patrice Kouame via swift-users <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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