[swift-users] UnsafeMutablePointer Swift 3 conversion
Andrew Trick
atrick at apple.com
Thu Sep 8 12:35:19 CDT 2016
> On Sep 8, 2016, at 4:04 AM, Gerard Iglesias <gerard_iglesias at me.com> wrote:
>
> Andrew,
>
> Thank you for the compliment ;)
>
> And thank you for the 2 advices
>
> And the question about use of size or stride ? I understand that the underlaying float data are aligned in this specific case, but I wonder in fact if the shader compiler align memory the same way the swift compiler do, I suppose yes unless it would be a nightmare, but murphy’s principle says me … take care ;)
Always use stride for contiguous in-memory values.
-Andy
>
> Thanks in advance
>
> Gerard
>
>> On 8 Sep 2016, at 07:21, Andrew Trick <atrick at apple.com <mailto:atrick at apple.com>> wrote:
>>
>>>
>>> On Sep 3, 2016, at 6:03 PM, Gerard Iglesias via swift-users <swift-users at swift.org <mailto: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 <http://swift.org/> today! I think it will be a big help.
>> https://swift.org/migration-guide/se-0107-migrate.html <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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>>>>>>>> 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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