[swift-users] UnsafeMutablePointer Swift 3 conversion
Andrew Trick
atrick at apple.com
Thu Sep 8 00:21:37 CDT 2016
> On Sep 3, 2016, at 6:03 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)
Gerard,
I like your code. A couple of things to consider:
1. If the memory has never been bound to a type (i.e. it's straight from MTLBuffer.newBuffer), then rather than “assuming” memory is bound to these types, you should just bind it here (substitute all your assumingMemoryBound(to: _) with bindMemory(to: _, capacity: 1). Think of it as two-phase initialization of the memory. First declare the memory's type (e.g. some structure that holds a bunch of floats), then write individual float values into the memory.
2. If you want the compiler to compute byte offsets for you like the original code, then can be done as follows:
let mainPtr = UnsafeMutableRawPointer(shadowPtr + 1).bindMemory(
to: MainPass.self, capacity: 1)
mainPtr.pointee = mainPassFrameData
...
However, your approach of computing byte offsets is more explicit.
My migration guide landed on swift.org today! I think it will be a big help.
https://swift.org/migration-guide/se-0107-migrate.html
-Andy
>> 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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