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[Xamarin.Android.Build.Tasks] use System.Reflection.Metadata in <Reso…
…lveAssemblies/> Context: https://github.com/dotnet/corefx/tree/master/src/System.Reflection.Metadata/src/System/Reflection/Metadata Context: https://github.com/jonathanpeppers/Benchmarks There is a new System.Reflection.Metadata library from corefx for reading .NET assemblies. It is a bit more performant than Mono.Cecil because it is a different library with different opinions. Some notes about System.Reflection.Metadata: - SRM has a forward "reader" style API - SRM uses lots of structs, and you have to do an additional call to lookup strings generally. - SRM, as far as I have seen, doesn't have APIs to modify and write out new assemblies. - SRM only supports "portable" pdb files. - SRM is not well documented yet. To discover usage, I read source code and/or unit tests. From my benchmark above, it seems that SRM is 10x faster on Windows/.NET framework and 5x faster on macOS/Mono. So it makes sense for use to use SRM when reading assemblies (and we don't need symbols), and continue with Mono.Cecil for the linker and other things that modify assemblies. There are a few places we can take advantage of SRM, but the simplest with a reasonable impact was `ResolveAssemblies`: Before: 320 ms ResolveAssemblies 1 calls After: 112 ms ResolveAssemblies 1 calls So a ~200ms savings on this MSBuild task, which runs on *every* build. This was the Xamarin.Forms test project in this repo: a build with no changes. ~~ Changes ~~ - Added a `MetadataResolver` type, as a way to cache `PEReader` instances. This is a comparable drop-in replacement for `DirectoryAssemblyResolver`. - `MonoAndroidHelper.IsReferenceAssembly` now uses `System.Reflection.Metadata` instead of `Mono.Cecil`. This is used in a few other MSBuild tasks. - A `MetadataExtensions` provides an extension method to simplify getting the full name of a custom attribute. We can add more here as needed. The resulting code *should* be the same, except we are using SRM over Mono.Cecil. ~~ Downstream ~~ We will need to add the following assemblies to the installer: - `System.Reflection.Metadata.dll` - `System.Collections.Immutable.dll`
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32 changes: 32 additions & 0 deletions
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src/Xamarin.Android.Build.Tasks/Utilities/DummyCustomAttributeProvider.cs
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| @@ -0,0 +1,32 @@ | ||
| using System.Reflection.Metadata; | ||
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| namespace Xamarin.Android.Tasks | ||
| { | ||
| /// <summary> | ||
| /// A helper type for System.Reflection.Metadata. Getting the value of custom attribute arguments is a bit convoluted, if you merely want the values. | ||
| /// | ||
| /// This interface allows usage such as: | ||
| /// CustomAttribute attribute = reader.GetCustomAttribute (handle); | ||
| /// CustomAttributeValue<object> decoded = attribute.DecodeValue (DummyCustomAttributeProvider.Instance); | ||
| /// </summary> | ||
| public class DummyCustomAttributeProvider : ICustomAttributeTypeProvider<object> | ||
| { | ||
| public static readonly DummyCustomAttributeProvider Instance = new DummyCustomAttributeProvider (); | ||
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| public object GetPrimitiveType (PrimitiveTypeCode typeCode) => null; | ||
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| public object GetSystemType () => null; | ||
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| public object GetSZArrayType (object elementType) => null; | ||
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| public object GetTypeFromDefinition (MetadataReader reader, TypeDefinitionHandle handle, byte rawTypeKind) => null; | ||
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| public object GetTypeFromReference (MetadataReader reader, TypeReferenceHandle handle, byte rawTypeKind) => null; | ||
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| public object GetTypeFromSerializedName (string name) => null; | ||
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| public PrimitiveTypeCode GetUnderlyingEnumType (object type) => default (PrimitiveTypeCode); | ||
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| public bool IsSystemType (object type) => false; | ||
| } | ||
| } |
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src/Xamarin.Android.Build.Tasks/Utilities/MetadataExtensions.cs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,21 @@ | ||
| using System.Reflection.Metadata; | ||
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| namespace Xamarin.Android.Tasks | ||
| { | ||
| public static class MetadataExtensions | ||
| { | ||
| public static string GetCustomAttributeFullName (this MetadataReader reader, CustomAttribute attribute) | ||
| { | ||
| if (attribute.Constructor.Kind == HandleKind.MemberReference) { | ||
| var ctor = reader.GetMemberReference ((MemberReferenceHandle)attribute.Constructor); | ||
| var type = reader.GetTypeReference ((TypeReferenceHandle)ctor.Parent); | ||
| return reader.GetString (type.Namespace) + "." + reader.GetString (type.Name); | ||
| } else if (attribute.Constructor.Kind == HandleKind.MethodDefinition) { | ||
| var ctor = reader.GetMethodDefinition ((MethodDefinitionHandle)attribute.Constructor); | ||
| var type = reader.GetTypeDefinition (ctor.GetDeclaringType ()); | ||
| return reader.GetString (type.Namespace) + "." + reader.GetString (type.Name); | ||
| } | ||
| return null; | ||
| } | ||
| } | ||
| } |
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src/Xamarin.Android.Build.Tasks/Utilities/MetadataResolver.cs
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|---|---|---|
| @@ -0,0 +1,61 @@ | ||
| using System; | ||
| using System.Collections.Generic; | ||
| using System.IO; | ||
| using System.Reflection.Metadata; | ||
| using System.Reflection.PortableExecutable; | ||
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| namespace Xamarin.Android.Tasks | ||
| { | ||
| /// <summary> | ||
| /// A replacement for DirectoryAssemblyResolver, using System.Reflection.Metadata | ||
| /// </summary> | ||
| public class MetadataResolver : IDisposable | ||
| { | ||
| readonly Dictionary<string, PEReader> cache = new Dictionary<string, PEReader> (); | ||
| readonly List<string> searchDirectories = new List<string> (); | ||
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| public MetadataReader GetAssemblyReader (string assemblyName) | ||
| { | ||
| var key = Path.GetFileNameWithoutExtension (assemblyName); | ||
| if (!cache.TryGetValue (key, out PEReader reader)) { | ||
| var assemblyPath = ResolveAssembly (assemblyName); | ||
| cache.Add (key, reader = new PEReader (File.OpenRead (assemblyPath))); | ||
| } | ||
| return reader.GetMetadataReader (); | ||
| } | ||
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| public void AddSearchDirectory (string directory) | ||
| { | ||
| directory = Path.GetFullPath (directory); | ||
| if (!searchDirectories.Contains (directory)) | ||
| searchDirectories.Add (directory); | ||
| } | ||
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| public string ResolveAssembly (string assemblyName) | ||
| { | ||
| string assemblyPath = assemblyName; | ||
| if (!assemblyPath.EndsWith (".dll", StringComparison.OrdinalIgnoreCase)) { | ||
| assemblyPath += ".dll"; | ||
| } | ||
| if (File.Exists (assemblyPath)) { | ||
| AddSearchDirectory (Path.GetDirectoryName (assemblyPath)); | ||
| return assemblyPath; | ||
| } | ||
| foreach (var dir in searchDirectories) { | ||
| var path = Path.Combine (dir, assemblyPath); | ||
| if (File.Exists (path)) | ||
| return path; | ||
| } | ||
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| throw new FileNotFoundException ($"Could not load assembly '{assemblyName}'.", assemblyName); | ||
| } | ||
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| public void Dispose () | ||
| { | ||
| foreach (var provider in cache.Values) { | ||
| provider.Dispose (); | ||
| } | ||
| cache.Clear (); | ||
| } | ||
| } | ||
| } |
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