Shaun Xu

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Shaun, the author of this blog is a semi-geek, clumsy developer, passionate speaker and incapable architect with about 10 years experience in .NET. He hopes to prove that software development is art rather than manufacturing. He's into cloud computing platform and technologies (Windows Azure, Aliyun) as well as WCF and ASP.NET MVC. Recently he's falling in love with JavaScript and Node.js.

Currently Shaun is working at IGT Technology Development (Beijing) Co., Ltd. as the architect responsible for product framework design and development.

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In my project there is a platform component which takes the responsible for controlling and monitoring all other components and it need to lead all other components' metadata when starting. We defined metadata in each component assembly with attributes and will be retrieved through .NET reflection. At the beginning of this project ,about 3 years ago, there are only 5 - 6 components and it takes about 10 - 20 seconds to reflect them. But with more and more components were introduced currently there will be more than 30 components installed in our system. Then we met a performance problem when system start up, it takes 60 - 80 seconds to scan all those assemblies to retrieve the metadata in my development workstation. And it takes several minutes in some of customers and testers machine since less hardware capability (slower CPU and less memory).

After reviewed the code I found there is no problem in our implementation. The main problem is we utilizes System.Reflection to retrieve metadata, the performance of System.Reflection is not that satisficed. After some investigation and research I found an alternative solution which is using Mono.Cecil to reflect .NET assembly.

We thought the best solution is to move all metadata information from assembly attributes to database or configuration file so that we can load them without using reflection technology. But since we also need to maintain backward capability, we must allow all existing components works for our new platform component. So we have to continue using attributes to store metadata.

 

We can find Mono.Cecil here. We also can add Mono.Cecil into our .NET project reference from NuGet package management in Visual Studio.

image

Below are the operations we are using defined in Mono.Cecil to replace System.Reflection.

System.Reflection Mono.Cecil
Assembly.LoadFrom() AssemblyDefinition.ReadAssembly()
CustomAttributeData.GetCustomAttributes(Assembly) AssemblyDefinition.CustomAttributes
Aassmebly.GetTypes() AssemblyDefinition.Modules.SelectMany(m => m.GetTypes())
Type.GetInterfaces() TypeDefinition.Interfaces
CustomAttributeData.GetCustomAttributes(Type) TypeDefinition.CustomAttributes
CustomAttributeData.Constructor.GetParameters() CustomAttribute.Constructor.Resolve().Parameters

Most of them are easy to learn and use. We load an assembly from the static class `AssemblyDefinition` and the static method `ReadAssembly` by passing the file path. Different from System.Reflection, it will NOT lock the assembly file. This means by using Mono.Cecil we don't need to create a new AppDomain to load the assembly and unload it at the end.

With the `AssemblyDefinition` we can retrieve attributes and types. Then we can use the `TypeDefinition` and `CustomAttribute` instances to retrieve the type name, interfaces it implements and the value defined in the attribute.

Just one thing need to be highlighted here, by default Mono.Cecil will reflect limited information from the targeting assembly. For example, let's say I have an assembly `MyClass.dll` and there's a class with a custom attribute attached, as well as implemented an interface those are defined in separated assemblies.

image

When we invoked `AssemblyDefinition.ReadAssembly` to `MyClass.dll`, Mono will only load this assembly but will NOT lock it.

image

Now we can retrieve the types defined in this assembly and the attributes, interfaces it associates. But since the attribute and interface were defined in other assemblies, when we invoke `CustomAttributes` and `Interfaces` they will return metadata that can be found in this assembly. For example we can retrieve the constructor of `MyAttrib` in type of `MethodReference`, which contains the parameter values and the arguments. But we cannot retrieve the parameter names since the definition of this attribute was in another assembly. To retrieve more information we need to invoke `Resolve` method to let Mono find the definition assembly of this type and load more information. We can also define the behavior how Mono find the relevant assemblies, which path Mono need to lookup. I will show the code later.

image

Similarly if we want to retrieve more information of the interface our class was implemented, we need to invoke `TypeReference.Resolve()`.

 

Below is the code I implemented in my project that using Mono.Cecil to retrieve metadata information from assemblies. In order to decouple from my business logic I created a set of interfaces represents all operations I need for reflection as below.

The `IReflector` interface is the main entry to let user load assembly.

   1: public interface IReflector
   2: {
   3:     IAssemblyReflector LoadAssembly(string path);
   4: }

`IAssemblyReflector` interface isolates operations that interact with assembly, such as retrieving attributes, types, name, file path, etc..

   1: public interface IAssemblyReflector
   2: {
   3:     IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute;
   4:  
   5:     IEnumerable<ITypeReflector> GetTypes();
   6:  
   7:     string Location { get; }
   8:  
   9:     string FileName { get; }
  10:  
  11:     string FullName { get; }
  12: }

With `ITypeReflector` interface we can retrieve attributes attached as well as interfaces it implements.

   1: public interface ITypeReflector
   2: {
   3:     IEnumerable<ITypeReflector> GetInterfaces();
   4:  
   5:     IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute;
   6:  
   7:     string FullName { get; }
   8:  
   9:     string Name { get; }
  10: }

With `IAttributeReflector` we can get values of the arguments and named property values from its constructor.

   1: public interface IAttributeReflector
   2: {
   3:     IDictionary<string, string> Values { get; }
   4: }

 

Below is the Mono.Cecil implementation of these interfaces. Notice that I invoked `Resolve` to load the definition assembly when retrieving interfaces and attribute values. I also tell Mono.Cecil to lookup relevant assemblies in the same folder of the assembly I'm loading.

   1: public class MonoReflector : IReflector
   2: {
   3:     public IAssemblyReflector LoadAssembly(string path)
   4:     {
   5:         var resolver = new DefaultAssemblyResolver();
   6:         resolver.AddSearchDirectory(Path.GetDirectoryName(path));
   7:         var reader = new ReaderParameters()
   8:         {
   9:             AssemblyResolver = resolver
  10:         };
  11:  
  12:         var assembly = AssemblyDefinition.ReadAssembly(path, reader);
  13:         return new MonoAssemblyReflector(assembly);
  14:     }
  15: }
  16:  
  17: public class MonoAssemblyReflector : IAssemblyReflector
  18: {
  19:     private AssemblyDefinition _assembly;
  20:  
  21:     public MonoAssemblyReflector(AssemblyDefinition assembly)
  22:     {
  23:         _assembly = assembly;
  24:     }
  25:  
  26:     public IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute
  27:     {
  28:         if (_assembly.HasCustomAttributes)
  29:         {
  30:             var expectedTypeName = typeof(T).Name;
  31:             return _assembly.CustomAttributes
  32:                 .Where(a => a.AttributeType.Name == expectedTypeName)
  33:                 .Select(a => new MonoAttributeReflector(a))
  34:                 .ToList();
  35:         }
  36:         else
  37:         {
  38:             return new IAttributeReflector[] { };
  39:         }
  40:     }
  41:  
  42:     public IEnumerable<ITypeReflector> GetTypes()
  43:     {
  44:         var result = new List<ITypeReflector>();
  45:         var modules = _assembly.Modules;
  46:         foreach (var module in modules)
  47:         {
  48:             var types = module.GetTypes();
  49:             foreach (var type in types)
  50:             {
  51:                 result.Add(new MonoTypeReflector(type));
  52:             }
  53:         }
  54:         return result;
  55:     }
  56:  
  57:     public string Location
  58:     {
  59:         get
  60:         {
  61:             return _assembly.MainModule.FullyQualifiedName;
  62:         }
  63:     }
  64:  
  65:     public string FileName
  66:     {
  67:         get
  68:         {
  69:             return _assembly.MainModule.Name;
  70:         }
  71:     }
  72:  
  73:     public string FullName
  74:     {
  75:         get
  76:         {
  77:             return _assembly.FullName;
  78:         }
  79:     }
  80: }
  81:  
  82: public class MonoTypeReflector : ITypeReflector
  83: {
  84:     private TypeDefinition _type;
  85:  
  86:     public MonoTypeReflector(TypeDefinition type)
  87:     {
  88:         _type = type;
  89:     }
  90:  
  91:     public IEnumerable<ITypeReflector> GetInterfaces()
  92:     {
  93:         return _type.Interfaces.Select(i => new MonoTypeReflector(i.Resolve()));
  94:     }
  95:  
  96:     public IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute
  97:     {
  98:         if (_type.HasCustomAttributes)
  99:         {
 100:             var expectedTypeName = typeof(T).Name;
 101:             return _type.CustomAttributes
 102:                 .Where(a => a.AttributeType.Name == expectedTypeName)
 103:                 .Select(a => new MonoAttributeReflector(a))
 104:                 .ToList();
 105:         }
 106:         else
 107:         {
 108:             return new IAttributeReflector[] { };
 109:         }
 110:     }
 111:  
 112:     public string FullName
 113:     {
 114:         get
 115:         {
 116:             return _type.FullName;
 117:         }
 118:     }
 119:  
 120:     public string Name
 121:     {
 122:         get
 123:         {
 124:             return _type.Name;
 125:         }
 126:     }
 127: }
 128:  
 129: public class MonoAttributeReflector : IAttributeReflector
 130: {
 131:     private CustomAttribute _attribute;
 132:     private IDictionary<string, string> _values;
 133:  
 134:     public MonoAttributeReflector(CustomAttribute attribute)
 135:     {
 136:         _attribute = attribute;
 137:     }
 138:  
 139:     public IDictionary<string, string> Values
 140:     {
 141:         get
 142:         {
 143:             if (_values == null)
 144:             {
 145:                 _values = new Dictionary<string, string>();
 146:                 var constructorArguments = _attribute.Constructor.Resolve().Parameters.Select(p => p.Name).ToList();
 147:                 var constructorParameters = _attribute.ConstructorArguments.Select(a => a.Value.ToString()).ToList();
 148:                 for (var i = 0; i < constructorArguments.Count; i++)
 149:                 {
 150:                     _values.Add(constructorArguments[i], constructorParameters[i]);
 151:                 }
 152:                 foreach (var prop in _attribute.Properties)
 153:                 {
 154:                     _values.Add(prop.Name, prop.Argument.Value.ToString());
 155:                 }
 156:             }
 157:             return _values;
 158:         }
 159:     }
 160: }

Below is the implementation by System.Reflection.

   1: public class DotNetAssemblyReflector : IAssemblyReflector
   2: {
   3:     private Assembly _assmebly;
   4:  
   5:     public DotNetAssemblyReflector(Assembly assmebly)
   6:     {
   7:         _assmebly = assmebly;
   8:     }
   9:  
  10:     public virtual IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute
  11:     {
  12:         List<CustomAttributeData> returnValue = new List<CustomAttributeData>();
  13:         var pCustomAttributeType = typeof(T);
  14:  
  15:         foreach (CustomAttributeData customAttributeData in CustomAttributeData.GetCustomAttributes(_assmebly))
  16:         {
  17:             if (customAttributeData.Constructor.DeclaringType.Name == pCustomAttributeType.Name)
  18:             {
  19:                 returnValue.Add(customAttributeData);
  20:             }
  21:         }
  22:  
  23:         return returnValue.Select(x => new DotNetAttributeReflector(x)).ToList();
  24:     }
  25:  
  26:     public string GetVersion()
  27:     {
  28:         string version = string.Empty;
  29:         var assemblyFileVersionCustomAttributeData = GetAttributes<AssemblyFileVersionAttribute>();
  30:         if (assemblyFileVersionCustomAttributeData.Count() == 1)
  31:         {
  32:             try
  33:             {
  34:                 var assemblyFileVersion = assemblyFileVersionCustomAttributeData.First().Values;
  35:                 version = assemblyFileVersion["version"];
  36:             }
  37:             catch (FormatException ex)
  38:             {
  39:                 // // Console.WriteLine(String.Format("Problem getting the assembly version: {0}", assembly.FullName));
  40:                 // // Console.WriteLine(ex);
  41:             }
  42:         }
  43:         return version;
  44:     }
  45:  
  46:     public IEnumerable<ITypeReflector> GetTypes()
  47:     {
  48:         return _assmebly.GetTypes().Select(t => new DotNetTypeReflector(t)).ToList();
  49:     }
  50:  
  51:     public string Location
  52:     {
  53:         get 
  54:         {
  55:             return _assmebly.Location;
  56:         }
  57:     }
  58:  
  59:     public string FileName
  60:     {
  61:         get 
  62:         {
  63:             return _assmebly.ManifestModule.Name;
  64:         }
  65:     }
  66:     
  67:     public string FullName
  68:     {
  69:         get 
  70:         {
  71:             return _assmebly.FullName;
  72:         }
  73:     }
  74: }
  75:  
  76: public class DotNetTypeReflector : ITypeReflector
  77: {
  78:     private Type _type;
  79:  
  80:     public DotNetTypeReflector(Type type)
  81:     {
  82:         _type = type;
  83:     }
  84:  
  85:     public IEnumerable<ITypeReflector> GetInterfaces()
  86:     {
  87:         return _type.GetInterfaces().Select(i => new DotNetTypeReflector(i)).ToList();
  88:     }
  89:  
  90:     public IEnumerable<IAttributeReflector> GetAttributes<T>() where T : Attribute
  91:     {
  92:         List<CustomAttributeData> returnValue = new List<CustomAttributeData>();
  93:         var pCustomAttributeType = typeof(T);
  94:  
  95:         foreach (CustomAttributeData customAttributeData in CustomAttributeData.GetCustomAttributes(_type))
  96:         {
  97:             if (customAttributeData.Constructor.DeclaringType.Name == pCustomAttributeType.Name)
  98:             {
  99:                 returnValue.Add(customAttributeData);
 100:             }
 101:         }
 102:  
 103:         return returnValue.Select(a => new DotNetAttributeReflector(a)).ToList();
 104:     }
 105:  
 106:     public string FullName
 107:     {
 108:         get 
 109:         {
 110:             return _type.FullName;
 111:         }
 112:     }
 113:  
 114:     public string Name
 115:     {
 116:         get 
 117:         {
 118:             return _type.Name;
 119:         }
 120:     }
 121: }
 122:  
 123:  
 124: public class DotNetAttributeReflector : IAttributeReflector
 125: {
 126:     private CustomAttributeData _attribute;
 127:     private IDictionary<string, string> _values;
 128:  
 129:     public IDictionary<string, string> Values
 130:     {
 131:         get
 132:         {
 133:             if (_values == null)
 134:             {
 135:                 Dictionary<string, string> returnValue = new Dictionary<string, string>();
 136:                 try
 137:                 {
 138:                     ParameterInfo[] ConstructorParameters = _attribute.Constructor.GetParameters();
 139:                     for (int i = 0; i < ConstructorParameters.Length; i++)
 140:                     {
 141:                         returnValue.Add(ConstructorParameters[i].Name, _attribute.ConstructorArguments[i].Value.ToString());
 142:                     }
 143:                 }
 144:                 catch (KeyNotFoundException ex)
 145:                 {
 146:                     // something is not matching up with constructor parameters and arguments
 147:                     // this will be a FormatException for our purposes, so we will wrap and rethrow
 148:                     throw;
 149:                 }
 150:                 foreach (CustomAttributeNamedArgument argument in _attribute.NamedArguments)
 151:                 {
 152:                     returnValue.Add(argument.MemberInfo.Name, argument.TypedValue.Value.ToString());
 153:                 }
 154:                 _values = returnValue;
 155:             }
 156:             return _values;
 157:         }
 158:     }
 159:  
 160:     public DotNetAttributeReflector(CustomAttributeData attribute)
 161:     {
 162:         _attribute = attribute;
 163:     }
 164: }
 165:  
 166: public class DotNetReflector : IReflector
 167: {
 168:     public IAssemblyReflector LoadAssembly(string path)
 169:     {
 170:         return new DotNetAssemblyReflector(Assembly.LoadFrom(path));
 171:     }
 172: }

 

Finally let's have a look on the performance result. I'm using Mono.Cecil and System.Reflection to retrieve the metadata information from all 38 components in my system. In .NET 4.0 and 4.5.1, Mono.Cecil took 4 seconds while System.Reflection took 21 seconds.

image

 

Hope this helps,

Shaun

All documents and related graphics, codes are provided "AS IS" without warranty of any kind.
Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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