From 9f2ff42da56ee19d789af9eff1d514059b506163 Mon Sep 17 00:00:00 2001
From: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date: Fri, 8 Oct 2021 07:58:22 +0200
Subject: [PATCH] [.NET/AudioUnit] Use [UnmanagedCallersOnly] instead of
 [MonoPInvokeCallback] for the ScheduledAudioFileRegionCallback function.
 (#12948)

Ref https://github.com/xamarin/xamarin-macios/issues/10470.
---
 src/AudioUnit/AUScheduledAudioFileRegion.cs | 23 ++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/AudioUnit/AUScheduledAudioFileRegion.cs b/src/AudioUnit/AUScheduledAudioFileRegion.cs
index f181b1198207..c62ea6c130e8 100644
--- a/src/AudioUnit/AUScheduledAudioFileRegion.cs
+++ b/src/AudioUnit/AUScheduledAudioFileRegion.cs
@@ -24,7 +24,11 @@ public class AUScheduledAudioFileRegion : IDisposable {
 		internal struct ScheduledAudioFileRegion
 		{
 			public AudioTimeStamp TimeStamp;
+#if NET
+			public unsafe delegate* unmanaged<IntPtr, IntPtr, AudioUnitStatus, void> CompletionHandler;
+#else
 			public ScheduledAudioFileRegionCompletionHandler CompletionHandler;
+#endif
 			public /* void * */ IntPtr CompletionHandlerUserData;
 			public IntPtr AudioFile;
 			public uint LoopCount;
@@ -51,9 +55,10 @@ public AUScheduledAudioFileRegion (AudioFile audioFile, AUScheduledAudioFileRegi
 			this.completionHandler = completionHandler;
 		}
 
+#if !NET
 		internal delegate void ScheduledAudioFileRegionCompletionHandler (
 			/* void * */IntPtr userData, 
-			/* ScheduledAudioFileRegion * */ref ScheduledAudioFileRegion fileRegion, 
+			/* ScheduledAudioFileRegion * */ IntPtr fileRegion,
 			/* OSStatus */ AudioUnitStatus result);
 
 		static readonly ScheduledAudioFileRegionCompletionHandler static_ScheduledAudioFileRegionCompletionHandler = new ScheduledAudioFileRegionCompletionHandler (ScheduledAudioFileRegionCallback);
@@ -61,7 +66,10 @@ internal delegate void ScheduledAudioFileRegionCompletionHandler (
 #if !MONOMAC
 		[MonoPInvokeCallback (typeof (ScheduledAudioFileRegionCompletionHandler))]
 #endif
-		static void ScheduledAudioFileRegionCallback (IntPtr userData, ref ScheduledAudioFileRegion fileRegion, AudioUnitStatus status)
+#else
+		[UnmanagedCallersOnly]
+#endif
+		static void ScheduledAudioFileRegionCallback (IntPtr userData, IntPtr fileRegion, AudioUnitStatus status)
 		{
 			if (userData == IntPtr.Zero)
 				return;
@@ -85,13 +93,22 @@ internal ScheduledAudioFileRegion GetAudioFileRegion ()
 			var ret = new ScheduledAudioFileRegion {
 				TimeStamp = TimeStamp,
 				CompletionHandlerUserData = ptr,
-				CompletionHandler = ptr != IntPtr.Zero ? static_ScheduledAudioFileRegionCompletionHandler : null,
 				AudioFile = AudioFile.Handle,
 				LoopCount = LoopCount,
 				StartFrame = StartFrame,
 				FramesToPlay = FramesToPlay
 			};
 
+			if (ptr != IntPtr.Zero) {
+				unsafe {
+#if NET
+					ret.CompletionHandler = &ScheduledAudioFileRegionCallback;
+#else
+					ret.CompletionHandler = static_ScheduledAudioFileRegionCompletionHandler;
+#endif
+				}
+			}
+
 			alreadyUsed = true;
 			return ret;
 		}