[CoreGraphics] Adjust CGPDFOperatorTable to not use a generic Action delegate. #11560
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…delegate.
* CoreCLR doesn't support generic Action delegates in reverse (P/Invokes), so
we need to find a different solution.
* The native CGPDFOperatorTable callback API is not very friendly to us,
because we can't pass it callback-specific data, which means that the
managed caller must conform to the FullAOT requirement of the managed
callback (must be a static function; must have a MonoPInvokeCallback
attribute).
* We can leverage the new function pointer syntax in C# 9 to make these
requirements enforced by the C# compiler (unmanaged function pointer +
UnmanagedCallersOnly attribute). The resulting API is still clunky to use,
but I don't see any way around that.
Fixes this monotouch-test failure with CoreCLR:
[FAIL] Tamarin : System.Runtime.InteropServices.MarshalDirectiveException : Cannot marshal 'parameter #3': Non-blittable generic types cannot be marshaled.
at CoreGraphics.CGPDFOperatorTable.CGPDFOperatorTableSetCallback(IntPtr table, String name, Action`2 callback)
at CoreGraphics.CGPDFOperatorTable.SetCallback(String name, Action`2 callback)
at MonoTouchFixtures.CoreGraphics.PDFScannerTest.Tamarin() in xamarin-macios/tests/monotouch-test/CoreGraphics/PDFScannerTest.cs:line 102
Ref: dotnet/runtime#32963
tj-devel709
reviewed
May 14, 2021
| // this won't work with AOT since the callback must be decorated with [MonoPInvokeCallback] | ||
| public void SetCallback (string name, Action<CGPDFScanner,object> callback) | ||
| { | ||
| if (name == null) | ||
| throw new ArgumentNullException ("name"); | ||
|
|
||
| if (callback == null) | ||
| CGPDFOperatorTableSetCallback (Handle, name, null); | ||
| CGPDFOperatorTableSetCallback (Handle, name, (CGPDFOperatorCallback) null); |
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Woah I don't recall seeing this before haha. A type cast for null! What does this do?
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@tj-devel709 imaging you are a compiler and you see:
public void CGPDFOperatorTableSetCallback (IntPtr handel, String name, CGPDFOperatorCallback callback) {...}
public void CGPDFOperatorTableSetCallback (IntPtr handel, String name, OtherObject obj) {..}
Later in the code I have:
CGPDFOperatorTableSetCallback (Handle, name, null);Which of the above overloads do you call??
And if you see:
CGPDFOperatorTableSetCallback (Handle, name, (CGPDFOperatorCallback) null);AFAIK you can also do:
CGPDFOperatorTableSetCallback (Handle, name, default(CGPDFOperatorCallback));which helps the compiler too without a cast.
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Ah thank you for explaining!
✅ [PR Build] Tests passed on Build. ✅Tests passed on Build. API diff✅ API Diff from stable View API diffAPI & Generator diff✅ API Diff (from PR only) (no change) 🎉 All 82 tests passed 🎉Pipeline on Agent XAMBOT-1104.BigSur' |
mandel-macaque
approved these changes
May 14, 2021
mandel-macaque
added
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dalexsoto
approved these changes
May 14, 2021
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we need to find a different solution.
because we can't pass it callback-specific data, which means that the
managed caller must conform to the FullAOT requirement of the managed
callback (must be a static function; must have a MonoPInvokeCallback
attribute).
requirements enforced by the C# compiler (unmanaged function pointer +
UnmanagedCallersOnly attribute). The resulting API is still clunky to use,
but I don't see any way around that.
Fixes this monotouch-test failure with CoreCLR:
Ref: dotnet/runtime#32963