[perf] Add unmanaged constraint to some APIs to allow pinning, and not manual GCHandle code (#7561)

Co-authored-by: Rolf Bjarne Kvinge <rolf@xamarin.com>
Co-authored-by: GitHub Actions Autoformatter <github-actions-autoformatter@xamarin.com>

src/AudioToolbox/AudioConverter.cs

@@ -643,26 +643,25 @@ namespace AudioToolbox {
 			return GetArray<AudioValueRange> (prop, sizeof (AudioValueRange));
 		}
 
-		unsafe T []? GetArray<T> (AudioConverterPropertyID prop, int elementSize)
+		unsafe T []? GetArray<T> (AudioConverterPropertyID prop, int elementSize) where T : unmanaged
 		{
 			int size;
 			bool writable;
 			if (AudioConverterGetPropertyInfo (Handle, prop, out size, out writable) != AudioConverterError.None)
 				return null;
 
-			var data = new T [size / elementSize];
-			var array_handle = GCHandle.Alloc (data, GCHandleType.Pinned); // This requires a pinned GCHandle, since it's not possible to use unsafe code to get the address of a generic object.
+			if (size == 0)
+				return Array.Empty<T> ();
 
-			try {
-				var ptr = array_handle.AddrOfPinnedObject ();
-				var res = AudioConverterGetProperty (Handle, prop, ref size, ptr);
+			var data = new T [size / elementSize];
+
+			fixed (T* ptr = data) {
+				var res = AudioConverterGetProperty (Handle, prop, ref size, (IntPtr) ptr);
 				if (res != 0)
 					return null;
 
 				Array.Resize (ref data, size / elementSize);
 				return data;
-			} finally {
-				array_handle.Free ();
 			}
 		}
 

src/AudioToolbox/AudioFormatAvailability.cs

@@ -65,26 +65,25 @@ namespace AudioToolbox {
 			return GetAvailable<AudioClassDescription> (AudioFormatProperty.Encoders, format);
 		}
 
-		unsafe static T []? GetAvailable<T> (AudioFormatProperty prop, AudioFormatType format)
+		unsafe static T []? GetAvailable<T> (AudioFormatProperty prop, AudioFormatType format) where T : unmanaged
 		{
 			uint size;
 			if (AudioFormatPropertyNative.AudioFormatGetPropertyInfo (prop, sizeof (AudioFormatType), ref format, out size) != 0)
 				return null;
 
-			var data = new T [size / Marshal.SizeOf (typeof (T))];
-			var array_handle = GCHandle.Alloc (data, GCHandleType.Pinned); // This requires a pinned GCHandle, since it's not possible to use unsafe code to get the address of a generic object.
+			if (size == 0)
+				return Array.Empty<T> ();
 
-			try {
-				var ptr = array_handle.AddrOfPinnedObject ();
-				var res = AudioFormatPropertyNative.AudioFormatGetProperty (prop, sizeof (AudioFormatType), ref format, ref size, ptr);
+			var data = new T [size / Marshal.SizeOf (typeof (T))];
+			fixed (T* ptr = data) {
+				var res = AudioFormatPropertyNative.AudioFormatGetProperty (prop, sizeof (AudioFormatType), ref format, ref size, (IntPtr) ptr);
 				if (res != 0)
 					return null;
-
-				Array.Resize (ref data, (int) size / Marshal.SizeOf (typeof (T)));
-				return data;
-			} finally {
-				array_handle.Free ();
 			}
+
+
+			Array.Resize (ref data, (int) size / sizeof (T));
+			return data;
 		}
 	}
 

tests/monotouch-test/AudioUnit/AudioUnitTest.cs

@@ -4,6 +4,8 @@
 
 #if !__WATCHOS__
 
+using System.Runtime.InteropServices;
+
 using NUnit.Framework;
 
 using Foundation;
@@ -80,6 +82,14 @@ namespace MonoTouchFixtures.AudioUnit {
 				var icon = component.CopyIcon (); // ensuring that the manual binding does not throw, we do not care about the result
 			});
 		}
+
+		[Test]
+		public unsafe void TestSizeOf()
+		{
+			Assert.AreEqual (sizeof (AudioFormat), Marshal.SizeOf (typeof (AudioFormat)));
+			Assert.AreEqual (sizeof (AudioValueRange), Marshal.SizeOf (typeof (AudioValueRange)));
+			Assert.AreEqual (sizeof (AudioClassDescription), Marshal.SizeOf (typeof (AudioClassDescription)));
+		}
 	}
 }