[.NET/CoreFoundation] Use [UnmanagedCallersOnly] instead of [MonoPInv…

…okeCallback] Partial Fix for #10470 (#15879)

src/CoreFoundation/CFRunLoop.cs

@@ -59,17 +59,27 @@ public enum CFRunLoopExitReason : int {
 
 	// CFRunLoop.h
 	[StructLayout (LayoutKind.Sequential)]
+#if NET
+	internal unsafe struct CFRunLoopSourceContext {
+#else
 	internal struct CFRunLoopSourceContext {
+#endif
 		public CFIndex Version;
 		public IntPtr Info;
 		public IntPtr Retain;
 		public IntPtr Release;
 		public IntPtr CopyDescription;
 		public IntPtr Equal;
 		public IntPtr Hash;
+#if NET
+		public delegate* unmanaged<IntPtr, IntPtr, IntPtr, void> Schedule;
+		public delegate* unmanaged<IntPtr, IntPtr, IntPtr, void> Cancel;
+		public delegate* unmanaged<IntPtr, void> Perform;
+#else
 		public IntPtr Schedule;
 		public IntPtr Cancel;
 		public IntPtr Perform;
+#endif
 	}
 
 #if NET
@@ -145,27 +155,41 @@ public abstract class CFRunLoopSourceCustom : CFRunLoopSource {
 		[DllImport (Constants.CoreFoundationLibrary)]
 		extern static /* CFRunLoopSourceRef */ IntPtr CFRunLoopSourceCreate (/* CFAllocatorRef */ IntPtr allocator, /* CFIndex */ nint order, /* CFRunLoopSourceContext* */ ref CFRunLoopSourceContext context);
 
+#if !NET
 		static ScheduleCallback ScheduleDelegate = (ScheduleCallback) Schedule;
 		static CancelCallback CancelDelegate = (CancelCallback) Cancel;
 		static PerformCallback PerformDelegate = (PerformCallback) Perform;
+#endif
 
 		protected CFRunLoopSourceCustom ()
 			: base (IntPtr.Zero, true)
 		{
 			gch = GCHandle.Alloc (this);
 			var ctx = new CFRunLoopSourceContext ();
 			ctx.Info = GCHandle.ToIntPtr (gch);
+#if NET
+			unsafe {
+				ctx.Schedule = &Schedule;
+				ctx.Cancel = &Cancel;
+				ctx.Perform = &Perform;
+			}
+#else
 			ctx.Schedule = Marshal.GetFunctionPointerForDelegate (ScheduleDelegate);
 			ctx.Cancel = Marshal.GetFunctionPointerForDelegate (CancelDelegate);
 			ctx.Perform = Marshal.GetFunctionPointerForDelegate (PerformDelegate);
+#endif
 
 			var handle = CFRunLoopSourceCreate (IntPtr.Zero, 0, ref ctx);
 			InitializeHandle (handle);
 		}
 
 		delegate void ScheduleCallback (IntPtr info, IntPtr runLoop, IntPtr mode);
 
+#if NET
+		[UnmanagedCallersOnly]
+#else
 		[MonoPInvokeCallback (typeof(ScheduleCallback))]
+#endif
 		static void Schedule (IntPtr info, IntPtr runLoop, IntPtr mode)
 		{
 			var source = GCHandle.FromIntPtr (info).Target as CFRunLoopSourceCustom;
@@ -182,7 +206,11 @@ static void Schedule (IntPtr info, IntPtr runLoop, IntPtr mode)
 
 		delegate void CancelCallback (IntPtr info, IntPtr runLoop, IntPtr mode);
 
+#if NET
+		[UnmanagedCallersOnly]
+#else
 		[MonoPInvokeCallback (typeof(CancelCallback))]
+#endif
 		static void Cancel (IntPtr info, IntPtr runLoop, IntPtr mode)
 		{
 			var source = GCHandle.FromIntPtr (info).Target as CFRunLoopSourceCustom;
@@ -199,7 +227,11 @@ static void Cancel (IntPtr info, IntPtr runLoop, IntPtr mode)
 
 		delegate void PerformCallback (IntPtr info);
 
+#if NET
+		[UnmanagedCallersOnly]
+#else
 		[MonoPInvokeCallback (typeof(PerformCallback))]
+#endif
 		static void Perform (IntPtr info)
 		{
 			var source = GCHandle.FromIntPtr (info).Target as CFRunLoopSourceCustom;