[src] Fix GC-safety issues in a number of APIs.

src/AddressBook/ABMultiValue.cs

@@ -184,13 +184,17 @@ static Exception CreateNotSupportedException ()
 		public T Value {
 			get {
 				AssertValid ();
-				return self.toManaged (ABMultiValue.CopyValueAtIndex (self.Handle, index));
+				var rv = self.toManaged (ABMultiValue.CopyValueAtIndex (self.Handle, index));
+				GC.KeepAlive (self);
+				return rv;
 			}
 			set {
 				if (IsReadOnly)
 					throw CreateNotSupportedException ();
 				AssertValid ();
-				if (ABMultiValue.ReplaceValueAtIndex (self.Handle, ToIntPtr (value), index) == 0)
+				var rv = ABMultiValue.ReplaceValueAtIndex (self.Handle, ToIntPtr (value), index);
+				GC.KeepAlive (self);
+				if (rv == 0)
 					throw new ArgumentException ("Value cannot be set");
 			}
 		}
@@ -212,14 +216,17 @@ public T Value {
 		public NSString? Label {
 			get {
 				AssertValid ();
-				return Runtime.GetNSObject<NSString> (ABMultiValue.CopyLabelAtIndex (self.Handle, index), true);
+				var rv = Runtime.GetNSObject<NSString> (ABMultiValue.CopyLabelAtIndex (self.Handle, index), true);
+				GC.KeepAlive (self);
+				return rv;
 			}
 			set {
 				if (IsReadOnly)
 					throw CreateNotSupportedException ();
 				AssertValid ();
 				ABMultiValue.ReplaceLabelAtIndex (self.Handle, value.GetHandle (), index);
 				GC.KeepAlive (value);
+				GC.KeepAlive (self);
 			}
 		}
 
@@ -243,7 +250,9 @@ public NSString? Label {
 		public int Identifier {
 			get {
 				AssertValid ();
-				return ABMultiValue.GetIdentifierAtIndex (self.Handle, index);
+				var rv = ABMultiValue.GetIdentifierAtIndex (self.Handle, index);
+				GC.KeepAlive (self);
+				return rv;
 			}
 		}
 	}

src/AudioToolbox/MusicTrack.cs

@@ -294,8 +294,10 @@ internal MusicTrack (MusicSequence sequence, IntPtr handle, bool owns)
 		protected override void Dispose (bool disposing)
 		{
 			if (Handle != IntPtr.Zero && Owns) {
-				if (sequence is not null)
+				if (sequence is not null) {
 					MusicSequenceDisposeTrack (sequence.Handle, Handle);
+					GC.KeepAlive (sequence);
+				}
 			}
 			sequence = null;
 			base.Dispose (disposing);

src/AudioUnit/AudioUnit.cs

@@ -625,10 +625,13 @@ public AudioStreamBasicDescription GetAudioFormat (AudioUnitScopeType scope, uin
 		///         <remarks>To be added.</remarks>
 		public AudioUnitStatus SetClassInfo (ClassInfoDictionary preset, AudioUnitScopeType scope = AudioUnitScopeType.Global, uint audioUnitElement = 0)
 		{
-			var ptr = preset.Dictionary.Handle;
+			var dictionary = preset.Dictionary;
+			var ptr = dictionary.Handle;
 			unsafe {
-				return AudioUnitSetProperty (Handle, AudioUnitPropertyIDType.ClassInfo, scope, audioUnitElement,
+				var rv = AudioUnitSetProperty (Handle, AudioUnitPropertyIDType.ClassInfo, scope, audioUnitElement,
 					&ptr, IntPtr.Size);
+				GC.KeepAlive (dictionary);
+				return rv;
 			}
 		}
 

src/CoreFoundation/CFArray.cs

@@ -117,8 +117,11 @@ public static unsafe NativeHandle Create (params INativeObject [] values)
 			var _values = c <= 256 ? stackalloc IntPtr [c] : new IntPtr [c];
 			for (int i = 0; i < c; ++i)
 				_values [i] = values [i].Handle;
+			IntPtr rv;
 			fixed (IntPtr* pv = _values)
-				return CFArrayCreate (IntPtr.Zero, (IntPtr) pv, c, kCFTypeArrayCallbacks_ptr);
+				rv = CFArrayCreate (IntPtr.Zero, (IntPtr) pv, c, kCFTypeArrayCallbacks_ptr);
+			GC.KeepAlive (values);
+			return rv;
 		}
 
 		/// <summary>Create a <see cref="CFArray" /> from an array of strings.</summary>

src/CoreFoundation/CFDictionary.cs

@@ -79,7 +79,10 @@ public static CFDictionary FromObjectsAndKeys (INativeObject [] objects, INative
 				v [i] = objects [i].Handle;
 			}
 
-			return new CFDictionary (CFDictionaryCreate (IntPtr.Zero, k, v, k.Length, KeyCallbacks, ValueCallbacks), true);
+			var rv = new CFDictionary (CFDictionaryCreate (IntPtr.Zero, k, v, k.Length, KeyCallbacks, ValueCallbacks), true);
+			GC.KeepAlive (keys);
+			GC.KeepAlive (objects);
+			return rv;
 		}
 
 		[DllImport (Constants.CoreFoundationLibrary)]

src/CoreFoundation/CFPreferences.cs

@@ -154,6 +154,7 @@ public static void SetAppValue (string key, object? value, NSString applicationI
 				} else if (value is string) {
 					using (var valueStr = new CFString ((string) value)) {
 						CFPreferencesSetAppValue (cfKey.Handle, valueStr.Handle, applicationId.Handle);
+						GC.KeepAlive (cfKey);
 						GC.KeepAlive (applicationId);
 					}
 
@@ -164,6 +165,7 @@ value is NSArray || value is CFArray ||
 					value is NSDictionary || value is CFDictionary ||
 					value is NSNumber || value is CFBoolean) {
 					CFPreferencesSetAppValue (cfKey.Handle, ((INativeObject) value).Handle, applicationId.Handle);
+					GC.KeepAlive (cfKey);
 					GC.KeepAlive (value);
 					GC.KeepAlive (applicationId);
 					return;
@@ -173,6 +175,8 @@ value is NSDictionary || value is CFDictionary ||
 				if (nsnumber is not null) {
 					using (nsnumber) {
 						CFPreferencesSetAppValue (cfKey.Handle, nsnumber.Handle, applicationId.Handle);
+						GC.KeepAlive (cfKey);
+						GC.KeepAlive (nsnumber);
 						GC.KeepAlive (applicationId);
 					}
 					return;

src/CoreGraphics/CGPDFDocument.cs

@@ -250,6 +250,7 @@ public CGPDFDictionary GetInfo ()
 		public void SetOutline (CGPDFOutlineOptions? options)
 		{
 			CGPDFContextSetOutline (Handle, options.GetHandle ());
+			GC.KeepAlive (options);
 		}
 
 		[SupportedOSPlatform ("ios")]

src/CoreMidi/MidiServices.cs

@@ -1839,7 +1839,9 @@ public class MidiDevice : MidiObject {
 		public int Add (string name, bool embedded, nuint numSourceEndpoints, nuint numDestinationEndpoints, MidiEntity newEntity)
 		{
 			using (NSString nsName = new NSString (name)) {
-				return MIDIDeviceAddEntity (GetCheckedHandle (), nsName.Handle, embedded ? (byte) 1 : (byte) 0, numSourceEndpoints, numDestinationEndpoints, newEntity.Handle);
+				var rv = MIDIDeviceAddEntity (GetCheckedHandle (), nsName.Handle, embedded ? (byte) 1 : (byte) 0, numSourceEndpoints, numDestinationEndpoints, newEntity.Handle);
+				GC.KeepAlive (newEntity);
+				return rv;
 			}
 		}
 
@@ -2542,7 +2544,9 @@ public nuint GetNumberOfDevices ()
 		///         <remarks>To be added.</remarks>
 		public int Add (MidiDevice device)
 		{
-			return MIDIDeviceListAddDevice (GetCheckedHandle (), device.Handle);
+			var rv = MIDIDeviceListAddDevice (GetCheckedHandle (), device.Handle);
+			GC.KeepAlive (device);
+			return rv;
 		}
 
 		internal override void DisposeHandle ()

src/CoreServices/FSEvents.cs

@@ -352,7 +352,8 @@ public FSEventStream (FSEventStreamCreateOptions options)
 				context.Release = &FreeGCHandle;
 			}
 
-			var allocator = options.Allocator.GetHandle ();
+			var allocatorObject = options.Allocator;
+			var allocator = allocatorObject.GetHandle ();
 			var sinceWhenId = options.SinceWhenId ?? FSEvent.SinceNowId;
 			var latency = options.Latency.TotalSeconds;
 			var flags = options.Flags |= (FSEventStreamCreateFlags) 0x1 /* UseCFTypes */;
@@ -366,13 +367,15 @@ public FSEventStream (FSEventStreamCreateOptions options)
 						&context,
 						options.DeviceToWatch.Value,
 						pathsToWatch.Handle, sinceWhenId, latency, flags);
+					GC.KeepAlive (allocatorObject);
 					GC.KeepAlive (pathsToWatch);
 				} else {
 					handle = FSEventStreamCreate (
 						allocator,
 						&EventsCallback,
 						&context,
 						pathsToWatch.Handle, sinceWhenId, latency, flags);
+					GC.KeepAlive (allocatorObject);
 					GC.KeepAlive (pathsToWatch);
 				}
 			}

src/CoreText/CTFontCollection.cs

@@ -123,10 +123,17 @@ internal CTFontCollection (NativeHandle handle, bool owns)
 		///         <remarks>
 		///         </remarks>
 		public CTFontCollection (CTFontCollectionOptions? options)
-			: base (CTFontCollectionCreateFromAvailableFonts (options.GetHandle ()), true, true)
+			: base (CreateFromAvailableFonts (options), true, true)
 		{
 		}
 
+		static IntPtr CreateFromAvailableFonts (CTFontCollectionOptions? options)
+		{
+			var rv = CTFontCollectionCreateFromAvailableFonts (options.GetHandle ());
+			GC.KeepAlive (options);
+			return rv;
+		}
+
 		[DllImport (Constants.CoreTextLibrary)]
 		static extern IntPtr CTFontCollectionCreateWithFontDescriptors (IntPtr queryDescriptors, IntPtr options);
 		static IntPtr Create (CTFontDescriptor []? queryDescriptors, CTFontCollectionOptions? options)
@@ -201,6 +208,7 @@ public CTFontDescriptor [] GetMatchingFontDescriptors ()
 		public CTFontDescriptor [] GetMatchingFontDescriptors (CTFontCollectionOptions? options)
 		{
 			var cfArrayRef = CTFontCollectionCreateMatchingFontDescriptorsWithOptions (Handle, options.GetHandle ());
+			GC.KeepAlive (options);
 			if (cfArrayRef == IntPtr.Zero)
 				return Array.Empty<CTFontDescriptor> ();
 			return CFArray.ArrayFromHandleFunc (cfArrayRef, fd => new CTFontDescriptor (fd, false), true)!;

src/CoreText/CTFramesetter.cs

@@ -112,10 +112,12 @@ public CGSize SuggestFrameSize (NSRange stringRange, CTFrameAttributes? frameAtt
 			fitRange = default;
 			unsafe {
 				fixed (NSRange* fitRangePtr = &fitRange) {
-					return CTFramesetterSuggestFrameSizeWithConstraints (
+					var rv = CTFramesetterSuggestFrameSizeWithConstraints (
 							Handle, stringRange,
 							frameAttributes.GetHandle (),
 							constraints, fitRangePtr);
+					GC.KeepAlive (frameAttributes);
+					return rv;
 				}
 			}
 		}

src/CoreText/CTTextTab.cs

@@ -111,6 +111,7 @@ public CTTextTab (CTTextAlignment alignment, double location)
 		public CTTextTab (CTTextAlignment alignment, double location, CTTextTabOptions? options)
 			: base (CTTextTabCreate (alignment, location, options.GetHandle ()), true, true)
 		{
+			GC.KeepAlive (options);
 		}
 		#endregion
 

src/CoreText/CTTypesetter.cs

@@ -159,6 +159,7 @@ public CTTypesetter (NSAttributedString value, CTTypesetterOptions? options)
 			: base (CTTypesetterCreateWithAttributedStringAndOptions (value.GetNonNullHandle (nameof (value)), options.GetHandle ()), true, true)
 		{
 			GC.KeepAlive (value);
+			GC.KeepAlive (options);
 		}
 		#endregion
 

src/CoreVideo/CVImageBuffer.cs

@@ -135,7 +135,10 @@ public CGColorSpace? ColorSpace {
 		[SupportedOSPlatform ("maccatalyst")]
 		public static int GetCodePoint (CVImageBufferYCbCrMatrix yCbCrMatrix)
 		{
-			return CVYCbCrMatrixGetIntegerCodePointForString (yCbCrMatrix.GetConstant ()!.Handle);
+			var constant = yCbCrMatrix.GetConstant ();
+			var rv = CVYCbCrMatrixGetIntegerCodePointForString (constant.GetHandle ());
+			GC.KeepAlive (constant);
+			return rv;
 		}
 
 		[SupportedOSPlatform ("ios")]
@@ -155,7 +158,10 @@ public static int GetCodePoint (CVImageBufferYCbCrMatrix yCbCrMatrix)
 		[SupportedOSPlatform ("maccatalyst")]
 		public static int GetCodePoint (CVImageBufferColorPrimaries color)
 		{
-			return CVColorPrimariesGetIntegerCodePointForString (color.GetConstant ()!.Handle);
+			var constant = color.GetConstant ();
+			var rv = CVColorPrimariesGetIntegerCodePointForString (constant.GetHandle ());
+			GC.KeepAlive (constant);
+			return rv;
 		}
 
 		[SupportedOSPlatform ("ios")]
@@ -175,7 +181,10 @@ public static int GetCodePoint (CVImageBufferColorPrimaries color)
 		[SupportedOSPlatform ("maccatalyst")]
 		public static int GetCodePoint (CVImageBufferTransferFunction function)
 		{
-			return CVTransferFunctionGetIntegerCodePointForString (function.GetConstant ()!.Handle);
+			var constant = function.GetConstant ();
+			var rv = CVTransferFunctionGetIntegerCodePointForString (constant.GetHandle ());
+			GC.KeepAlive (constant);
+			return rv;
 		}
 
 		[SupportedOSPlatform ("ios")]

src/CoreVideo/CVPixelBuffer.cs

@@ -224,6 +224,7 @@ static unsafe extern CVReturn CVPixelBufferCreateWithBytes (
 					DictionaryContainerHelper.GetHandle (pixelBufferAttributes),
 					&handle);
 			}
+			GC.KeepAlive (pixelBufferAttributes);
 
 			if (status != CVReturn.Success) {
 				gchandle.Free ();
@@ -370,6 +371,7 @@ static unsafe extern CVReturn CVPixelBufferCreateWithPlanarBytes (
 					}
 				}
 			}
+			GC.KeepAlive (pixelBufferAttributes);
 
 			if (status != CVReturn.Success) {
 				ReleasePlanarBytesCallbackImpl (data_handle_ptr, IntPtr.Zero, 0, 0, IntPtr.Zero);

src/CoreVideo/CVPixelBufferPool.cs

@@ -144,6 +144,7 @@ unsafe extern static CVReturn CVPixelBufferPoolCreatePixelBufferWithAuxAttribute
 			unsafe {
 				error = CVPixelBufferPoolCreatePixelBufferWithAuxAttributes (IntPtr.Zero, Handle, allocationSettings.GetHandle (), &pb);
 			}
+			GC.KeepAlive (allocationSettings);
 			if (error != CVReturn.Success)
 				return null;
 

src/Darwin/SystemLog.cs

@@ -236,8 +236,17 @@ public IEnumerable<Message> Search (Message msg)
 		{
 			if (msg is null)
 				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (msg));
+			// The native asl_search call is done here (and not in the iterator method below) to
+			// keep 'msg' alive across the native call. If it were done in the iterator, the C#
+			// compiler would hoist 'this' and 'msg' into fields of the generated state machine, and
+			// the GC.KeepAlive call wouldn't reliably keep 'msg' alive across the native call.
 			var search = asl_search (Handle, msg.Handle);
 			GC.KeepAlive (msg);
+			return EnumerateSearchResults (search);
+		}
+
+		static IEnumerable<Message> EnumerateSearchResults (IntPtr search)
+		{
 			IntPtr mh;
 
 			while ((mh = aslresponse_next (search)) != IntPtr.Zero)

src/Foundation/NSDecimal.cs

@@ -240,7 +240,10 @@ public override string ToString ()
 		{
 			unsafe {
 				fixed (NSDecimal* self = &this) {
-					return new NSString (NSDecimalString (self, NSLocale.CurrentLocale.Handle));
+					var currentLocale = NSLocale.CurrentLocale;
+					var rv = new NSString (NSDecimalString (self, currentLocale.Handle));
+					GC.KeepAlive (currentLocale);
+					return rv;
 				}
 			}
 		}

src/Foundation/NSFastEnumerator.cs

@@ -52,6 +52,7 @@ void Fetch ()
 		{
 			unsafe {
 				count = NSFastEnumerator.objc_msgSend (collection.Handle, Selector.GetHandle ("countByEnumeratingWithState:objects:count:"), state, &state->array1, (nuint) NSFastEnumerationState.ArrayLength);
+				GC.KeepAlive (collection);
 				if (!started) {
 					started = true;
 					mutationValue = *state->mutationsPtr;

src/ImageIO/CGImageDestination.cs

@@ -407,7 +407,9 @@ public bool CopyImageSource (CGImageSource image, CGCopyImageSourceOptions? opti
 		public void AddAuxiliaryDataInfo (CGImageAuxiliaryDataType auxiliaryImageDataType, CGImageAuxiliaryDataInfo? auxiliaryDataInfo)
 		{
 			using (var dict = auxiliaryDataInfo?.Dictionary) {
-				CGImageDestinationAddAuxiliaryDataInfo (Handle, auxiliaryImageDataType.GetConstant ().GetHandle (), dict.GetHandle ());
+				var constant = auxiliaryImageDataType.GetConstant ();
+				CGImageDestinationAddAuxiliaryDataInfo (Handle, constant.GetHandle (), dict.GetHandle ());
+				GC.KeepAlive (constant);
 			}
 		}
 	}

src/ImageIO/CGImageSource.cs

@@ -511,7 +511,9 @@ public CGImageSourceStatus GetStatus (int index)
 		[SupportedOSPlatform ("maccatalyst")]
 		public CGImageAuxiliaryDataInfo? CopyAuxiliaryDataInfo (nuint index, CGImageAuxiliaryDataType auxiliaryImageDataType)
 		{
-			var ptr = CGImageSourceCopyAuxiliaryDataInfoAtIndex (Handle, index, auxiliaryImageDataType.GetConstant ().GetHandle ());
+			var constant = auxiliaryImageDataType.GetConstant ();
+			var ptr = CGImageSourceCopyAuxiliaryDataInfoAtIndex (Handle, index, constant.GetHandle ());
+			GC.KeepAlive (constant);
 			if (ptr == IntPtr.Zero)
 				return null;
 

src/NearbyInteraction/NIAlgorithmConvergenceStatusReasonValues.cs

@@ -28,7 +28,10 @@ public partial class NIAlgorithmConvergenceStatusReasonValues {
 		[UnsupportedOSPlatform ("macos")]
 		public static NSString GetConvergenceStatusReason (NIAlgorithmConvergenceStatusReason reason)
 		{
-			return Runtime.GetNSObject<NSString> (NIAlgorithmConvergenceStatusReasonDescription (reason.GetConstant ().GetHandle ()))!;
+			var constant = reason.GetConstant ();
+			var rv = Runtime.GetNSObject<NSString> (NIAlgorithmConvergenceStatusReasonDescription (constant.GetHandle ()))!;
+			GC.KeepAlive (constant);
+			return rv;
 		}
 	}
 }

src/QuickLook/Thumbnail.cs

@@ -69,8 +69,12 @@ public static partial class QLThumbnailImage {
 
 			if (scaleFactor != 1 && iconMode != false) {
 				dictionary = new NSMutableDictionary ();
-				dictionary.LowlevelSetObject ((NSNumber) scaleFactor, OptionScaleFactorKey.Handle);
-				dictionary.LowlevelSetObject (iconMode ? CFBoolean.TrueHandle : CFBoolean.FalseHandle, OptionIconModeKey.Handle);
+				var scaleFactorKey = OptionScaleFactorKey;
+				dictionary.LowlevelSetObject ((NSNumber) scaleFactor, scaleFactorKey.Handle);
+				GC.KeepAlive (scaleFactorKey);
+				var iconModeKey = OptionIconModeKey;
+				dictionary.LowlevelSetObject (iconMode ? CFBoolean.TrueHandle : CFBoolean.FalseHandle, iconModeKey.Handle);
+				GC.KeepAlive (iconModeKey);
 			}
 
 			var handle = QLThumbnailImageCreate (IntPtr.Zero, url.Handle, maxThumbnailSize, dictionary.GetHandle ());