Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataWeb / Server / System / Data / Services / Caching / MetadataCache.cs / 1305376 / MetadataCache.cs
//---------------------------------------------------------------------- //// Copyright (c) Microsoft Corporation. All rights reserved. // //// Provides a class to cache metadata information. // // // @owner [....] //--------------------------------------------------------------------- namespace System.Data.Services.Caching { using System; using System.Collections.Generic; using System.Data.EntityClient; using System.Data.Objects; using System.Diagnostics; using System.Threading; ////// Use this class to cache metadata through MetadataCacheItem instances. /// internal static class MetadataCache { ///AppDomain-wide cache for metadata items. private static Dictionarycache = new Dictionary (new MetadataCacheKey.Comparer()); /// Reader/writer lock for AppDomain private static ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion); ///. Adds a new cache item, and returns the item that is put in the cache. /// Type of service with metadata being cached. /// /// Data context instance being cached, possibly segmenting the cache /// space for. /// /// Item being added. /// The item being put in the cache (possibly an existing one). ///This method is thread-safe but not re-entrant. internal static MetadataCacheItem AddCacheItem(Type serviceType, object dataContextInstance, MetadataCacheItem item) { Debug.Assert(serviceType != null, "serviceType != null"); Debug.Assert(dataContextInstance != null, "dataContextInstance != null"); Debug.Assert(item != null, "item != null"); MetadataCacheKey key = new MetadataCacheKey(serviceType, dataContextInstance as ObjectContext); MetadataCacheItem result; cacheLock.EnterWriteLock(); try { // If another thread beat the current thread, we return the // previously created item, which has a higher chance of // having survived a garbage collection already. if (!cache.TryGetValue(key, out result)) { cache.Add(key, item); result = item; } } finally { cacheLock.ExitWriteLock(); } Debug.Assert(result != null, "result != null -- a null item is never returned."); Debug.Assert( result == TryLookup(serviceType, dataContextInstance), "result == TryLookup(serviceType, dataContextInstance) -- instance from cache is being returned."); return result; } ///Tries to look up metadata for the specifed service type and context instance. /// Type of service with metadata being cached. /// /// Data context instance being cached, possibly segmenting the cache /// space for. /// /// The cached metadata item, if one exists. ///This method is thread-safe but not re-entrant. internal static MetadataCacheItem TryLookup(Type serviceType, object dataContextInstance) { Debug.Assert(serviceType != null, "serviceType != null"); Debug.Assert(dataContextInstance != null, "dataContextInstance != null"); MetadataCacheKey key = new MetadataCacheKey(serviceType, dataContextInstance as ObjectContext); MetadataCacheItem result; cacheLock.EnterReadLock(); try { cache.TryGetValue(key, out result); } finally { cacheLock.ExitReadLock(); } return result; } ///This type is used as the key in the metadata cache. internal struct MetadataCacheKey { ///Connection string used to segment service type. private readonly string dataContextConnection; ///Hash code for this instance. private readonly int hashCode; ///Service type. private readonly Type serviceType; ///Initializes a new MetadataCacheKey instance. /// Service type for key. /// Data context instace for key, possibly null. internal MetadataCacheKey(Type serviceType, ObjectContext dataContextInstance) { Debug.Assert(serviceType != null, "serviceType != null"); this.serviceType = serviceType; this.dataContextConnection = null; this.hashCode = this.serviceType.GetHashCode(); if (dataContextInstance != null) { EntityConnection connection = dataContextInstance.Connection as EntityConnection; if (connection != null) { this.dataContextConnection = new EntityConnectionStringBuilder(connection.ConnectionString).Metadata; this.hashCode ^= this.dataContextConnection.GetHashCode(); } } } ///Comparer for metadata cache keys. internal class Comparer : IEqualityComparer{ /// Compares the specified keys. /// First key. /// Second key. ///true if public bool Equals(MetadataCacheKey x, MetadataCacheKey y) { return x.dataContextConnection == y.dataContextConnection && x.serviceType == y.serviceType; } ///equals , false otherwise. Gets the hash code for the object. /// Object. ///The hash code for this key. public int GetHashCode(MetadataCacheKey obj) { return obj.hashCode; } } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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