[DRAFT] Add a managed static registrar. Fixes #17324.

docs/managed-static-registrar.md

@@ -0,0 +1,227 @@
+# Managed static registrar
+
+The managed static registrar is a variation of the static registrar where we
+don't use features the NativeAOT compiler doesn't support (most notably
+metadata tokens).
+
+It also takes advantage of new features in C# and managed code since the
+original static registrar code was written - in particular it tries to do as
+much as possible in managed code instead of native code, as well as various
+other performance improvements. The actual performance characteristics
+compared to the original static registrar will vary between the specific
+exported method signatures, but in general it's expected that method calls
+from native code to managed code will be faster.
+
+In order to make the managed static registrar easily testable and debuggable,
+it's also implemented for the other runtimes as well (Mono and CoreCLR as
+well), as well as when not using AOT in any form.
+
+## Design
+
+### Exported methods
+
+For each method exported to Objective-C, the managed static registrar will
+generate a managed method we'll call directly from native code, and which does
+all the marshalling.
+
+This method will have the [UnmanagedCallersOnly] attribute, so that it doesn't
+need any additional marshalling from the managed runtime - which makes it
+possible to obtain a native function pointer for it. It will also have a
+native entry point, which means that for AOT we can just directly call it from
+the generated Objective-C code.
+
+Given the following method:
+
+```csharp
+class AppDelegate : NSObject, IUIApplicationDelegate {
+    // this method is written by the app developer
+    public override bool FinishedLaunching (UIApplication app, NSDictionary options)
+    {
+        // ...
+    }
+}
+```
+
+The managed static registrar will add the following method to the `AppDelegate` class:
+
+```csharp
+class AppDelegate {
+    [UnmanagedCallersOnly (EntryPoint = "__registrar__uiapplicationdelegate_didFinishLaunching")]
+    static byte __registrar__DidFinishLaunchingWithOptions (IntPtr handle, IntPtr selector, IntPtr p0, IntPtr p1)
+    {
+        var obj = Runtime.GetNSObject (handle);
+        var p0Obj = (UIApplication) Runtime.GetNSObject (p0);
+        var p1Obj = (NSDictionary) Runtime.GetNSObject (p1);
+        var rv = obj.DidFinishLaunchingWithOptions (p0Obj, p1Obj);
+        return rv ? (byte) 1 : (byte) 0;
+    }
+}
+```
+
+and the generated Objective-C code will look something like this:
+
+```objective-c
+extern BOOL __registrar__uiapplicationdelegate_init (AppDelegate self, SEL _cmd, UIApplication* p0, NSDictionary* p1);
+
+@interface AppDelegate : NSObject<UIApplicationDelegate, UIApplicationDelegate> {
+}
+    -(BOOL) application:(UIApplication *)p0 didFinishLaunchingWithOptions:(NSDictionary *)p1;
+@end
+@implementation AppDelegate {
+}
+    -(BOOL) application:(UIApplication *)p0 didFinishLaunchingWithOptions:(NSDictionary *)p1
+    {
+        return __registrar__uiapplicationdelegate_didFinishLaunching (self, _cmd, p0, p1);
+    }
+@end
+```
+
+Note: the actual code is somewhat more complex in order to properly support
+managed exceptions and a few other corner cases.
+
+### Type mapping
+
+The runtime needs to quickly and efficiently do lookups between an Objective-C
+type and the corresponding managed type. In order to support this, the managed
+static registrar will add lookup tables in each assembly. The managed static
+registrar will create a numeric ID for each managed type, which is then
+emitted into the generated Objective-C code, and which we can use to look up
+the corresponding managed type. There is also a table in Objective-C that maps
+between the numeric ID and the corresponding Objective-C type.
+
+We also need to be able to find the wrapper type for interfaces representing
+Objective-C protocols - this is accomplished by generating a table in
+unmanaged code that maps the ID for the interface to the ID for the wrapper
+type.
+
+This is all supported by the `ObjCRuntime.IManagedRegistrar.LookTypeId` and
+`ObjCRuntime.IManagedRegistrar.Lookup` methods.
+
+Note that in many ways the type ID is similar to the metadata token for a type
+(and is sometimes referred to as such in the code, especially code that
+already existed before the managed static registrar was implemented).
+
+### Method mapping
+
+When AOT-compiling code, the generated Objective-C code can call the entry
+point for the UnmanagedCallersOnly trampoline directly (the AOT compiler will
+emit a native symbol with the name of the entry point).
+
+However, when no AOT-compiling code, the generated Objective-C code needs to
+find the function pointer for the UnmanagedCallersOnly methods. This is
+implemented using another lookup table in managed code.
+
+For technical reasons, this implemented using multiple levels of functions if
+there are a significant number of UnmanagedCallersOnly methods, because it
+seems the JIT will compile the target for every function pointer in a method,
+even if tha function pointer isn't loaded at runtime. This means that if
+there's 1.000 methods in the lookup table, the JIT will have to compile all
+the 1.000 methods the first time the lookup method is called if the lookup was
+implemented in a single function, even if the lookup method will eventually
+just find a single callback.
+
+This might be easier to describe with some code.
+
+Instead of this:
+
+```csharp
+class __Registrar_Callbacks__ {
+    IntPtr LookupUnmanagedFunction (int id)
+    {
+        switch (id) {
+        case 0: return (IntPtr) (delegate* unmanaged<void>) &Callback0;
+        case 1: return (IntPtr) (delegate* unmanaged<void>) &Callback1;
+        ...
+        case 999: return (IntPtr) (delegate* unmanaged<void>) &Callback999;
+        }
+        return (IntPtr) -1);
+    }
+}
+```
+
+we do this instead:
+
+```csharp
+class __Registrar_Callbacks__ {
+    IntPtr LookupUnmanagedFunction (int id)
+    {
+        if (id < 100)
+            return LookupUnmanagedFunction_0 (id);
+        if (id < 200)
+            return LookupUnmanagedFunction_1 (id);
+        ...
+        if (id < 1000)
+            LookupUnmanagedFunction_9 (id);
+        return (IntPtr) -1;
+    }
+
+    IntPtr LookupUnmanagedFunction_0 (int id)
+    {
+        switch (id) {
+        case 0: return (IntPtr) (delegate* unmanaged<void>) &Callback0;
+        case 1: return (IntPtr) (delegate* unmanaged<void>) &Callback1;
+        /// ...
+        case 9: return (IntPtr) (delegate* unmanaged<void>) &Callback9;
+        }
+        return (IntPtr) -1;
+    }
+
+
+    IntPtr LookupUnmanagedFunction_1 (int id)
+    {
+        switch (id) {
+        case 10: return (IntPtr) (delegate* unmanaged<void>) &Callback10;
+        case 11: return (IntPtr) (delegate* unmanaged<void>) &Callback11;
+        /// ...
+        case 19: return (IntPtr) (delegate* unmanaged<void>) &Callback19;
+        }
+        return (IntPtr) -1;
+    }
+}
+```
+
+
+### Generation
+
+All the generated IL is done in two separate custom linker steps. The first
+one, ManagedRegistrarStep, will generate the UnmanagedCallersOnly trampolines
+for every method exported to Objective-C. This happens before the trimmed has
+done any work (i.e. before marking), because the generated code will cause
+more code to be marked (and this way we don't have to replicate what the
+trimmer does when it traverses IL and metadata to figure out what else to
+mark).
+
+The trimmer will then trim away any UnmanagedCallersOnly trampoline that's no
+longer needed because the target method has been trimmed away.
+
+On the other hand, the lookup tables for the type mapping is done after
+trimming, because we only want to add types that aren't trimmed away to the
+lookup tables (otherwise we'd end up causing all those types to be kept).
+
+## Interpreter / JIT
+
+When not using the AOT compiler, we need to look up the native entry points
+for UnmanagedCallersOnly methods at runtime. In order to support this, the
+managed static registrar will add lookup tables in each assembly. The managed
+static registrar will create a numeric ID for each UnmanagedCallersOnly
+method, which is then emitted into the generated Objective-C code, and which
+we can use to look up the managed UnmanagedCallersOnly method at runtime (in
+the lookup table).
+
+This is the `ObjCRuntime.IManagedRegistrar.LookupUnmanagedFunction` method.
+
+## Performance
+
+Preliminary testing shows the following:
+
+### macOS
+
+Calling an exported managed method from Objective-C is 3-6x faster for simple method signatures.
+
+### Mac Catalyst
+
+Calling an exported managed method from Objective-C is 30-50% faster for simple method signatures.
+
+## References
+
+* https://github.com/dotnet/runtime/issues/80912

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -557,6 +557,10 @@
 			<_ExtraTrimmerArgs Condition="('$(_PlatformName)' == 'iOS' Or '$(_PlatformName)' == 'tvOS') And '$(_SdkIsSimulator)' == 'true'">$(_ExtraTrimmerArgs) --feature ObjCRuntime.Runtime.Arch.IsSimulator true</_ExtraTrimmerArgs>
 			<_ExtraTrimmerArgs Condition="('$(_PlatformName)' == 'iOS' Or '$(_PlatformName)' == 'tvOS') And '$(_SdkIsSimulator)' != 'true'">$(_ExtraTrimmerArgs) --feature ObjCRuntime.Runtime.Arch.IsSimulator false</_ExtraTrimmerArgs>
 
+			<!-- Set managed static registrar value -->
+			<_ExtraTrimmerArgs Condition="'$(Registrar)' == 'managed-static'">$(_ExtraTrimmerArgs) --feature ObjCRuntime.Runtime.IsManagedStaticRegistrar true</_ExtraTrimmerArgs>
+			<_ExtraTrimmerArgs Condition="'$(Registrar)' != 'managed-static'">$(_ExtraTrimmerArgs) --feature ObjCRuntime.Runtime.IsManagedStaticRegistrar false</_ExtraTrimmerArgs>
+
 			<!-- Enable serialization discovery. Ref: https://github.com/xamarin/xamarin-macios/issues/15676 -->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --enable-serialization-discovery</_ExtraTrimmerArgs>
 
@@ -589,6 +593,7 @@
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="MonoTouch.Tuner.RegistrarRemovalTrackingStep" />
 			<!-- TODO: these steps should probably run after mark. -->
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.Steps.PreMarkDispatcher" />
+			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.ManagedRegistrarStep" Condition="'$(Registrar)' == 'managed-static'" />
 
 			<!--
 				IMarkHandlers which run during Mark
@@ -601,6 +606,11 @@
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.Steps.MarkDispatcher" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.Steps.PreserveSmartEnumConversionsHandler" />
 
+			<!--
+				pre-sweep custom steps
+			-->
+			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="SweepStep" Type="Xamarin.Linker.ManagedRegistrarLookupTablesStep" Condition="'$(Registrar)' == 'managed-static'" />
+
 			<!--
 				post-sweep custom steps
 			-->

runtime/delegates.t4

@@ -667,6 +667,14 @@
 		) {
 			WrappedManagedFunction = "InvokeConformsToProtocol",
 		},
+
+		new XDelegate ("void *", "IntPtr", "xamarin_lookup_unmanaged_function",
+			"const char *", "IntPtr", "assembly",
+			"const char *", "IntPtr", "symbol",
+			"int32_t", "int", "id"
+		) {
+			WrappedManagedFunction = "LookupUnmanagedFunction",
+		},
 	};
 	delegates.CalculateLengths ();
 #><#+

runtime/runtime.m

@@ -136,7 +136,7 @@
 
 enum InitializationFlags : int {
 	InitializationFlagsIsPartialStaticRegistrar = 0x01,
-	/* unused									= 0x02,*/
+	InitializationFlagsIsManagedStaticRegistrar = 0x02,
 	/* unused									= 0x04,*/
 	/* unused									= 0x08,*/
 	InitializationFlagsIsSimulator				= 0x10,
@@ -2736,6 +2736,30 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
 	[message release];
 }
 
+void
+xamarin_registrar_dlsym (void **function_pointer, const char *assembly, const char *symbol, int32_t id)
+{
+	if (*function_pointer != NULL)
+		return;
+
+	*function_pointer = dlsym (RTLD_MAIN_ONLY, symbol);
+	if (*function_pointer != NULL)
+		return;
+
+	GCHandle exception_gchandle = INVALID_GCHANDLE;
+	*function_pointer = xamarin_lookup_unmanaged_function (assembly, symbol, id, &exception_gchandle);
+	if (*function_pointer != NULL)
+		return;
+
+	if (exception_gchandle != INVALID_GCHANDLE)
+		xamarin_process_managed_exception_gchandle (exception_gchandle);
+
+	// This shouldn't really happen
+	NSString *msg = [NSString stringWithFormat: @"Unable to load the symbol '%s' to call managed code: %@", symbol, xamarin_print_all_exceptions (exception_gchandle)];
+	NSLog (@"%@", msg);
+	@throw [[NSException alloc] initWithName: @"SymbolNotFoundException" reason: msg userInfo: NULL];
+}
+
 /*
  * File/resource lookup for assemblies
  *
@@ -3195,6 +3219,16 @@ -(enum XamarinGCHandleFlags) xamarinGetFlags
 	return xamarin_debug_mode;
 }
 
+void
+xamarin_set_is_managed_static_registrar (bool value)
+{
+	if (value) {
+		options.flags = (InitializationFlags) (options.flags | InitializationFlagsIsManagedStaticRegistrar);
+	} else {
+		options.flags = (InitializationFlags) (options.flags & ~InitializationFlagsIsManagedStaticRegistrar);
+	}
+}
+
 bool
 xamarin_is_managed_exception_marshaling_disabled ()
 {

runtime/xamarin/runtime.h

@@ -254,6 +254,7 @@ void			xamarin_check_objc_type (id obj, Class expected_class, SEL sel, id self,
 #endif
 
 void			xamarin_set_gc_pump_enabled (bool value);
+void			xamarin_set_is_managed_static_registrar (bool value);
 
 void			xamarin_process_nsexception (NSException *exc);
 void			xamarin_process_nsexception_using_mode (NSException *ns_exception, bool throwManagedAsDefault, GCHandle *output_exception);
@@ -295,6 +296,15 @@ void			xamarin_printf (const char *format, ...);
 void			xamarin_vprintf (const char *format, va_list args);
 void			xamarin_install_log_callbacks ();
 
+/*
+ * Looks up a native function pointer for a managed [UnmanagedCallersOnly] method.
+ *     function_pointer: the return value, lookup will only be performed if this points to NULL.
+ *     assembly: the assembly to look in. Might be NULL if the app was not built with support for loading additional assemblies at runtime.
+ *     symbol: the symbol to loop up. Can be NULL to save space (this value isn't used except in error messages).
+ *     id: a numerical id for faster lookup (than doing string comparisons on the symbol name).
+ */
+void			xamarin_registrar_dlsym (void **function_pointer, const char *assembly, const char *symbol, int32_t id);
+
 /*
  * Wrapper GCHandle functions that takes pointer sized handles instead of ints,
  * so that we can adapt our code incrementally to use pointers instead of ints

src/Foundation/NSArray.cs

@@ -295,6 +295,19 @@ static public T [] ArrayFromHandle<T> (NativeHandle handle) where T : class, INa
 			return ret;
 		}
 
+		static Array ArrayFromHandle (NativeHandle handle, Type elementType)
+		{
+			if (handle == NativeHandle.Zero)
+				return null;
+
+			var c = (int) GetCount (handle);
+			var rv = Array.CreateInstance (elementType, c);
+			for (int i = 0; i < c; i++) {
+				rv.SetValue (UnsafeGetItem (handle, (nuint) i, elementType), i);
+			}
+			return rv;
+		}
+
 		static public T [] EnumsFromHandle<T> (NativeHandle handle) where T : struct, IConvertible
 		{
 			if (handle == NativeHandle.Zero)
@@ -395,6 +408,18 @@ static T UnsafeGetItem<T> (NativeHandle handle, nuint index) where T : class, IN
 			return Runtime.GetINativeObject<T> (val, false);
 		}
 
+		static object UnsafeGetItem (NativeHandle handle, nuint index, Type type)
+		{
+			var val = GetAtIndex (handle, index);
+			// A native code could return NSArray with NSNull.Null elements
+			// and they should be valid for things like T : NSDate so we handle
+			// them as just null values inside the array
+			if (val == NSNull.Null.Handle)
+				return null;
+
+			return Runtime.GetINativeObject (val, false, type);
+		}
+
 		// can return an INativeObject or an NSObject
 		public T GetItem<T> (nuint index) where T : class, INativeObject
 		{