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The PropertyInfoManager is responsible for managing all the properties that have been registered for each business object type using the RegisterProperty() method. This type is found in the Csla.Core. FieldManager namespace. Each time RegisterProperty() is called, it is associating an IPropertyInfo object with a specific business object type. For each business object type, PropertyInfoManager maintains a list of IPropertyInfo objects that describe the properties registered for that type. This means that it also has a list of all the business object types, which is maintained in a Dictionary, as you can see in the PropertyInfoManager code: private static Dictionary<Type, List<IPropertyInfo>> _propertyInfoCache; This Dictionary is indexed by a Type object, representing the type of each business object with registered properties. The value is a List of IPropertyInfo objects, each containing metadata about a property registered to that type.
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The hard part about this class is that its methods need to be thread-safe. In many cases, it will be used in a multithreaded environment, such as in ASP.NET, so access to this Dictionary and to each individual List object must be wrapped with locking code. The PropertyInfoCache property does this for the Dictionary itself: private static object _cacheLock = new object(); private static Dictionary<Type, List<IPropertyInfo>> PropertyInfoCache { get { if (_propertyInfoCache == null) { lock (_cacheLock) { if (_propertyInfoCache == null) _propertyInfoCache = new Dictionary<Type, List<IPropertyInfo>>(); } } return _propertyInfoCache; } } The private field _cacheLock is used to lock the region of code that creates the Dictionary if it doesn t already exist. Notice how the code checks the existence of the Dictionary both before and after the lock statement. This avoids a race condition, where multiple threads could wait on the lock and run the code inside the lock, even though the first thread to reach that point would have already created the Dictionary. Similarly, the GetPropertyListCache() method protects both the use of the Dictionary and the creation of individual List objects for each business object type. public static List<IPropertyInfo> GetPropertyListCache(Type objectType) { var cache = PropertyInfoCache; List<IPropertyInfo> list = null; if (!(cache.TryGetValue(objectType, out list))) { lock (cache) { if (!(cache.TryGetValue(objectType, out list))) { list = new List<IPropertyInfo>(); cache.Add(objectType, list); } } } return list; } This method uses the PropertyInfoCache property to safely get a reference to the Dictionary. It then uses the TryGetValue() method to attempt to retrieve the specific List<IPropertyInfo> for the business object type. If that is unsuccessful, a lock statement is used to ensure that only one thread can run the code that creates and adds the new List object to the Dictionary. Notice how the TryGetValue() is called inside the lock statement to prevent multiple threads from getting that far and creating duplicate List objects.
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The RegisterProperty() method is used to register properties for a business object type by adding an IPropertyInfo object to the correct List. This method also employs locking to avoid threading issues. public static PropertyInfo<T> RegisterProperty<T>( Type objectType, PropertyInfo<T> info) { var list = GetPropertyListCache(objectType); lock (list) { list.Add(info); list.Sort(); } return info; } In this case, the GetPropertyListCache() method is used to safely get a reference to the List object, then a lock statement is used to block access to that specific List object so only one property can be registered at a time. Notice that the list is sorted as each item is added. This ensures that the list is sorted when all properties have been registered and guarantees that the values are in the same order each time. Later in the chapter, I ll discuss how these values provide a numeric index into the list of managed field values for each business object. The order of the properties is very important. Of course, the RegisterProperty() methods are called when .NET does its initialization of the static fields on each class. You might expect that those method calls would occur in the same order all the time, thanks to .NET. Unfortunately, I don t trust that to be the case across C# and VB, or between the 32- and 64-bit .NET runtimes. As you ll see later, these values must be in the same order in a client/server situation, even if the client is 32-bit .NET in VB and the server is 64-bit .NET in C#. Sorting the property objects ensures that they re in the same order in the list, regardless of the programming language or the .NET runtime version. Finally, the GetRegisteredProperties() method returns a list of properties registered for a business object type. Since this method is public, there s no way to know what the calling code will do with the result, so this method doesn t return the actual List. Instead, it returns a copy of the data in a new List. public static List<IPropertyInfo> GetRegisteredProperties(Type objectType) { var list = GetPropertyListCache(objectType); lock (list) return new List<IPropertyInfo>(list); } The original List object is locked to block any RegisterProperty() calls from changing the list while the items are being copied to the result. BusinessBase and ReadOnlyBase use the PropertyInfoManager to manage all the details around tracking the properties registered for each business type.
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