[.NET/AudioUnit] Use [UnmanagedCallersOnly] instead of [MonoPInvokeCallback] Partial Fix for #10470 #15808

stephen-hawley · 2022-08-30T14:32:05Z

OK - this works, but you're not going to like it.
Why? Well, it comes down to this struct here:

#if NET
        [StructLayout (LayoutKind.Sequential)]
        public unsafe struct AURenderCallbackStruct
        {
                public delegate* unmanaged<IntPtr, AudioRenderActionFlags*, AudioTimeStamp*, uint, uint, IntPtr, AudioUnitStatus> Proc;
//              public delegate* unmanaged<IntPtr, int*, AudioTimeStamp*, uint, uint, IntPtr, int> Proc;
                public IntPtr ProcRefCon;
        }
#else
        [StructLayout (LayoutKind.Sequential)]
        struct AURenderCallbackStruct
        {
                public Delegate Proc;
                public IntPtr ProcRefCon;
        }
#endif

What you're seeing in the NET section is what I think the struct should be for the field Proc which represents the correct signature for the callback function. However, if I use this, I get the following errors:

AudioUnit/AudioUnit.cs(142,100): error CS0246: The type or namespace name 'AudioUnitStatus' could not be found (are you missing a using directive or an assembly reference?)
AudioUnit/AudioUnit.cs(142,38): error CS0246: The type or namespace name 'AudioRenderActionFlags' could not be found (are you missing a using directive or an assembly reference?)

Which is particularly interesting for 3 reasons:
1 - both types are in scope - the actual declaration of a function that meets the contract works with no issue.
2 - making the types fully qualified makes no difference
3 - I AUGraph.cs, which I did first, I initially made a local version of the callback which was declared as an inner type but otherwise declared identically and it worked (!!)

So yes, this is a greasy, greasy, hack.
Why does it work? The types we're smudging are really just 32 bit integers, so no harm no foul. Well, a little foul.

…llback] Partial Fix for xamarin#10470

src/AudioUnit/AudioUnit.cs

rolfbjarne

Welcome to the joy of porting broken code...

rolfbjarne · 2022-08-31T16:07:09Z

src/AudioUnit/AUGraph.cs

+					foreach (RenderDelegate renderer in renderers) {
+						var tempActionFlags = *_ioActionFlags;
+						var tempTimeStamp = *_inTimeStamp;
+						renderer (tempActionFlags, tempTimeStamp, _inBusNumber, _inNumberFrames, buffers);


The temporary values here are unnecessary, because due to an incorrect binding, the ioActionFlags and inTimeStamp values aren't updated by the renderer callback:

Suggested change

renderer (tempActionFlags, tempTimeStamp, _inBusNumber, _inNumberFrames, buffers);

renderer (*_ioActionFlags, *_inTimeStamp, _inBusNumber, _inNumberFrames, buffers);

These arguments should be ref arguments in the RenderDelegate:

xamarin-macios/src/AudioUnit/AudioUnit.cs

Line 132 in 4c36652

public delegate AudioUnitStatus RenderDelegate (AudioUnitRenderActionFlags actionFlags, AudioTimeStamp timeStamp, uint busNumber, uint numberFrames, AudioBuffers data);

But that would be a breaking change, so we can't do that (we'd have to add (and correct) API instead of changing the existing one).

In any case, that's completely out of scope for this PR. I'd just make the .NET code just as broken as the non-.NET code, and maybe we'll get around to fixing it properly one day.

Huh. I looked at this through a peephole and just saw ref args and figured that I should honor the ref-ness.

rolfbjarne · 2022-08-31T16:07:40Z

src/AudioUnit/AUGraph.cs

+#if NET
+				AudioUnitRenderActionFlags tempActionFlags = *actionFlags;
+				var tempTimeStamp = *timeStamp;
+				var returnValue = callback (tempActionFlags, tempTimeStamp, busNumber, numberFrames, buffers);


Just one left now!

src/AudioUnit/AudioUnit.cs

vs-mobiletools-engineering-service2 · 2022-09-01T10:08:18Z

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0 tests crashed, 206 tests failed, 4126 tests passed.

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3 tests failed, 225 tests passed.

trimmode link/Mac Catalyst [dotnet]/Debug [dotnet]: Failed (Test run failed.
Tests run: 129 Passed: 121 Inconclusive: 0 Failed: 1 Ignored: 7)
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Tests run: 129 Passed: 120 Inconclusive: 0 Failed: 1 Ignored: 8)
introspection/watchOS 32-bits - simulator/Debug (watchOS 6.0): Crashed Known issue: HE0038)

	renderer (tempActionFlags, tempTimeStamp, _inBusNumber, _inNumberFrames, buffers);
	renderer (_ioActionFlags, _inTimeStamp, _inBusNumber, _inNumberFrames, buffers);

[.NET/AudioUnit] Use [UnmanagedCallersOnly] instead of [MonoPInvokeCallback] Partial Fix for #10470 #15808

[.NET/AudioUnit] Use [UnmanagedCallersOnly] instead of [MonoPInvokeCallback] Partial Fix for #10470 #15808

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edited

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edited