[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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