Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/FactoryGenerator.cs

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+//------------------------------------------------------------------------------
+// <copyright file="FactoryGenerator.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+#if !DONTUSEFACTORYGENERATOR
+
+using System;
+using System.Reflection;
+using System.Reflection.Emit;
+using System.Threading;
+using System.Security;
+using System.Security.Permissions;
+
+namespace System.Web.Util {
+    /*
+     * 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 = (ISomeInterface) 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) 2003 Microsoft Corporation
+     */
+
+    internal class FactoryGenerator {
+        private Type _factoryInterface;
+        private Type _returnedType;
+        private MethodInfo _methodToOverride;
+        private ModuleBuilder _dynamicModule = null;
+        private Type[] _emptyParameterList = new Type[] { };
+        private Type[] _interfacesToImplement;
+
+        internal 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", new Type[0]);
+            if (_methodToOverride.ReturnType != _returnedType) {
+                throw new ArgumentException(SR.GetString(SR.FactoryInterface));
+            }
+
+            // This will be needed later, when building the dynamic class.
+            _interfacesToImplement = new Type[1];
+            _interfacesToImplement[0] = factoryInterface;
+        }
+
+        // A type must be public and have a parameterless constructor, in order for us to be able to
+        // create a factory for the type.  Throws if either of these conditions are not true.
+        internal static void CheckPublicParameterlessConstructor(Type type) {
+            if (type == null) {
+                throw new ArgumentNullException("type");
+            }
+
+            if (!(type.IsPublic || type.IsNestedPublic)) {
+                throw new InvalidOperationException(SR.GetString(SR.FactoryGenerator_TypeNotPublic, type.Name));
+            }
+
+            ConstructorInfo constructor = type.GetConstructor(Type.EmptyTypes);
+            if (constructor == null) {
+                throw new InvalidOperationException(SR.GetString(SR.FactoryGenerator_TypeHasNoParameterlessConstructor, type.Name));
+            }
+        }
+
+        private static String GetUniqueCompilationName() {
+            return Guid.NewGuid().ToString().Replace('-', '_');
+        }
+
+        Type GetFactoryTypeWithAssert(Type type) {
+            CheckPublicParameterlessConstructor(type);
+
+            // Create the dynamic assembly if needed.
+            Type factoryType;
+
+            if (_dynamicModule == null) {
+                lock (this) {
+                    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
+                                                                    true, //isSynchronized
+                                                                    null  //assembly attributes
+                                                                    );
+
+                        // 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 <type_constructor>
+            //      ret
+
+            ILGenerator il = method.GetILGenerator();
+            ConstructorInfo cons = type.GetConstructor(Type.EmptyTypes);
+            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();
+
+            return factoryType;
+        }
+
+        internal IWebObjectFactory CreateFactory(Type type) {
+            Debug.Trace("FactoryGenerator", "Creating generator for type " + type.FullName);
+
+            Type factoryType = GetFactoryTypeWithAssert(type);
+
+            // Create the type. This is the only place where Activator.CreateInstance is used,
+            // reducing the calls to it from 1 per instance to 1 per type.
+            return (IWebObjectFactory) Activator.CreateInstance(factoryType);
+        }
+    }
+
+}
+
+#endif