xenadmin/XenModel/ServerDBs/TypeCache.cs

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 *     following disclaimer. 
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
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using System;
using System.Collections.Generic;
using System.Reflection;

namespace XenAdmin.ServerDBs
{
    /// <summary>
    /// Class for caching XAPI types by name. Used by <see cref="DbProxy"/>.
    /// </summary>
    internal static class TypeCache
    {
        private static readonly Dictionary<String, TypeCacheEntry> Entries = new Dictionary<string, TypeCacheEntry>();
        private static readonly object Lck = new object();

        private static TypeCacheEntry GetEntry(string className)
        {
            Util.ThrowIfStringParameterNullOrEmpty(className, "className");

            TypeCacheEntry entry;
            lock (Lck)
            {
                if (!Entries.TryGetValue(className, out entry))
                {
                    entry = new TypeCacheEntry(className);
                    Entries.Add(className, entry);
                }
            }
            return entry;
        }

        /// <summary>
        /// Gets the XAPI <see cref="Type"/> for the specified name.
        /// (assembly.GetType("XenAPI." + className, true, true))
        /// </summary>
        /// <param name="className">The name for which the XAPI <see cref="Type"/> is required.</param>
        /// <returns>The XAPI <see cref="Type"/> for the specified name.</returns>
        public static Type GetClassType(string className)
        {
            return GetEntry(className).ClassType;
        }

        /// <summary>
        /// Gets the XAPI Proxy <see cref="Type"/> for the specified name.
        /// (assembly.GetType("XenAPI.Proxy_" + className, true, true))
        /// </summary>
        /// <param name="className">The name for which the XAPI <see cref="Type"/> is required.</param>
        /// <returns>The XAPI <see cref="Type"/> for the specified name.</returns>
        public static Type GetProxyType(string className)
        {
            return GetEntry(className).ProxyType;
        }

        /// <summary>
        /// Gets the <see cref="Type"/> of the field of the specified name on the specified class.
        /// </summary>
        /// <param name="className">Name of the class on which the field resides.</param>
        /// <param name="fieldName">Name of the field for which the XPI <see cref="Type"/> is required.</param>
        /// <returns>The <see cref="Type"/> of the field of the specified name on the specified class.</returns>
        public static Type GetFieldType(string className, string fieldName)
        {
            Util.ThrowIfStringParameterNullOrEmpty(fieldName, "fieldName");
            
            return GetEntry(className).GetFieldType(fieldName);
        }

        private class TypeCacheEntry
        {
            private readonly Dictionary<string, Type> _fieldTypes = new Dictionary<string, Type>();
            public readonly Type ProxyType;
            public readonly Type ClassType;
            private readonly object _lck = new object();

            public TypeCacheEntry(string className)
            {
                Assembly assembly = Assembly.Load(new AssemblyName("XenModel"));
                ProxyType = assembly.GetType("XenAPI.Proxy_" + className, true, true);
                ClassType = assembly.GetType("XenAPI." + className, true, true);
            }

            public Type GetFieldType(string fieldName)
            {
                Type output;
                lock (_lck)
                {
                    if (!_fieldTypes.TryGetValue(fieldName, out output))
                    {
                        output = null;
                        FieldInfo fi = ProxyType.GetField(fieldName, BindingFlags.IgnoreCase | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);

                        if (fi != null)
                        {
                            output = fi.FieldType;
                            _fieldTypes.Add(fieldName, output);
                        }
                    }
                }
                return output;
            }
        }
    }
}