Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / MIT / System / Web / UI / MobileControls / FactoryGenerator.cs / 1305376 / FactoryGenerator.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- using System; using System.Collections; using System.Reflection; using System.Reflection.Emit; using System.Threading; using System.Security; using System.Security.Permissions; using System.Web.Util; namespace System.Web.UI.MobileControls { /* * Factory Generator class * A factory generator is useful for cases where a large number of late-bound * classes need to be instantiated. * * Normally, to create an instance of type t, you call the following code: * * ISomeInterface o = Activator.CreateInstance(t); * * This assumes that the default constructor is used, and that the type t * implements the interface ISomeInterface. * * The factory generator, on the other hand, can use reflection emit APIs * to dynamically generate a class factory for t. The generated class has * the equivalent of the following code: * * class X : ISomeInterfaceFactory * { * public ISomeInterface CreateInstance() * { * return new t(); * } * } * * It then instantiates and returns an object of this type. You can then * call CreateInstance to create an instance of the type, which is * significantly faster. * * A single instance of a FactoryGenerator can generate factories for * multiple types. However, it builds all these types into a single * dynamically generated assembly. CLR implementation prevents this * assembly from being unloaded until the process exits. * * The FactoryGenerator is (almost) a templated type. It takes two * types in its constructor: * * returnedType is the type common to all classes for which factories * are to be generated. In the example above, this would be * ISomeInterface. * factoryInterface is the interface implemented by the dynamically * generated class factory, and should include a method named * CreateInstance, that takes no parameters and returns an object * of the type specified by returnedType. In the example above, * this would be ISomeInterfaceFactory. * * Copyright (c) 2001 Microsoft Corporation */ [Obsolete("The System.Web.Mobile.dll assembly has been deprecated and should no longer be used. For information about how to develop ASP.NET mobile applications, see http://go.microsoft.com/fwlink/?LinkId=157231.")] internal class FactoryGenerator { private Type _factoryInterface; private Type _returnedType; private MethodInfo _methodToOverride; private ModuleBuilder _dynamicModule = null; private Type[] _emptyParameterList = new Type[] { }; private Type[] _interfacesToImplement; private object _instanceLock = new object(); private Hashtable _factoryTable = new Hashtable(); private static FactoryGenerator _factoryGenerator; private static object _factoryGeneratorLock = new object(); // VSWhidbey 459555: We only need one instance of FactoryGenerator per app domain, // so we mark all constructors as private so enforce the usage of the static // StaticFactoryGenerator property. private FactoryGenerator() : this(typeof(object), typeof(IWebObjectFactory)) { } private FactoryGenerator(Type returnedType, Type factoryInterface) { _returnedType = returnedType; _factoryInterface = factoryInterface; // Get the CreateInstance method, and make sure it has // the correct signature. _methodToOverride = factoryInterface.GetMethod("CreateInstance"); if (_methodToOverride.ReturnType != _returnedType || _methodToOverride.GetParameters().Length != 0) { throw new InvalidOperationException(SR.GetString(SR.FactoryGenerator_Error_FactoryInterface)); } // This will be needed later, when building the dynamic class. _interfacesToImplement = new Type[1]; _interfacesToImplement[0] = factoryInterface; } internal static FactoryGenerator StaticFactoryGenerator { get { if (_factoryGenerator == null) { lock (_factoryGeneratorLock) { if (_factoryGenerator == null) { _factoryGenerator = new FactoryGenerator(); } } } return _factoryGenerator; } } private static String GetUniqueCompilationName() { return Guid.NewGuid().ToString().Replace('-', '_'); } internal /*public*/ Object GetFactory(Type type) { // Create the dynamic assembly if needed. Object o = _factoryTable[type]; if (o != null) { return o; } lock (_instanceLock) { o = _factoryTable[type]; if (o != null) { return o; } Type factoryType; if (_dynamicModule == null) { // Use a unique name for each assembly. String name = GetUniqueCompilationName(); AssemblyName assemblyName = new AssemblyName(); assemblyName.Name = "A_" + name; // Create a new assembly. AssemblyBuilder newAssembly = Thread.GetDomain().DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run, null, //directory to persist assembly null, //evidence copied from caller null, //requiredPermissions null, //optionalPermissions null, //refusedPermissions true //isSynchronized ); // Create a single module in the assembly. _dynamicModule = newAssembly.DefineDynamicModule("M_" + name); } // Give the factory a unique name. String typeName = GetUniqueCompilationName(); TypeBuilder factoryTypeBuilder = _dynamicModule.DefineType("T_" + typeName, TypeAttributes.Public, typeof(Object), _interfacesToImplement); // Define the CreateInstance method. It must be virtual to be an interface implementation. MethodBuilder method = factoryTypeBuilder.DefineMethod("CreateInstance", MethodAttributes.Public | MethodAttributes.Virtual, _returnedType, null); // Generate IL. The generated IL corresponds to "return new type()" // newobj// ret ILGenerator il = method.GetILGenerator(); ConstructorInfo cons = type.GetConstructor(_emptyParameterList); il.Emit(OpCodes.Newobj, cons); il.Emit(OpCodes.Ret); // Specify that this method implements CreateInstance from the inherited interface. factoryTypeBuilder.DefineMethodOverride(method, _methodToOverride); // Bake in the type. factoryType = factoryTypeBuilder.CreateType(); // Create the type. This is the only place where Activator.CreateInstance is used, // reducing the calls to it from 1 per adapter instance to 1 per adapter type. object factory = Activator.CreateInstance(factoryType); _factoryTable[type] = factory; return factory; } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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